Common OBD-II Problems

OBD-II has now been in our faces for a "Quarter Century" and even though it works fairly efficiently to control the hydro-carbon emissions in post '96 vehicles to some degree, it isn't as effective as some people would've liked, in terms of its diagnostic accuracy or as transparent and simplistic in its use to aid the layman.  On the flip side, many people with several mechanics among them completely abhors OBD-II and sees it more as a hindrance that a help and even add that they prefer cars not to have OBD-II. Since its inception, OBD-II has stymied mechanics globally, especially when the OBD-II system shuts down the engine and turns on the  EPC Light or Check Engine Light. And today, some 25 years later most car owners and mechanics still suffer fits effects yet endure the wrath of OBD-II. However, regardless of what we as lay people say, OBD-II is here to stay and we cannot wish it or will it away. 

Genuine Volkswagen / Audi Harness Mfg Part #: 1KD971658

Personally I think OBD-II is a great in all aspects and incarnations however it has its drawbacks. OBD-II  does place car owners at a huge disadvantage and at risk when it fails. Purely because the problems are not evident but rather masked by the mysteries of electronics technology. This very often leaves them stranded and in a dangerous situations when stuck in the middle of nowhere. With the result that even the DIY car owners cannot do any repair work themselves, but have to resort to phoning  a salvage company to come  load their vehicle onto  a rollback.  Unless of course they have previously invested in a OBD-II scanner  and is able to check for DTC error codes.  But as the saying goes, "most people only lock the stable after the horse has bolted". 

Another drawback of OBD-II is that since car owners in general do not own diagnostic scanners; so they have to rely on some mechanic workshop or mechanical to tell them what problems they've encountered with their vehicle but only once its repaired. Considering most mechanics / repair shops repair OBD-II errors by substituting parts until the cause of the problem is  solved. Merely because they don't even understand the workings of OBD-II well enough to pinpoint problems with any great success. For most of us, this type of hit-&-miss approach comes as an un-bugeted expense, which most car owners can ill-afford especially after having to pay the exorbitant rollback cost.

I believe there are thousands more vehicle owners today, interested in their own vehicle's maintenance and there are even more inclined towards DIY repairs than ever before because of ODB-II. Their motivating factor being the high cost of automotive repairs vs the low cost of ODB-II diagnostic scanners. Albeit that the lower cost scanners bordering on cheap doesn't do such a fantastic diagnostic scan as their more expensive counter parts. 

NEW GENERATION CARS

Hopefully, the next generation of automobiles will be released with onboard diagnostic scanners incorporated directly into the vehicle's infotainment system. Seeing that these fancy units are comprised of  several discrete devices built into the same platform.  It's quite common for the average touch screen infotainment systems to have features ranging from  Built-in Bluetooth to Built-in WIFI which supports WiFi hot-spot broadcasting. Integrated phone connectivity for calls. Some even have rear view camera support. 

Others have fully fledged full-format 1080P video decoding, and USB functionality with multi-format audio and multi-band radio, coupled to dedicated dual voice-coil subwoofer and surround sound speakers. Not to mention Internet APP download capability.  Some include mirror and link for both Android and IOS Phones and a Global Positioning System (GPS) for navigation. All thanks to the magic of powerful multi-core processors and microprocessor embedded systems. 

I'd say adding an OBD-II scanner in place of one of these gadgets would be more beneficial 

So, throwing in a pretty decent quality OBD-II scanner into such a menagerie of tech wouldn't be such a biggie for car manufacturers and the cost wouldn't be prohibitively expensive either.  But since we not at that point in automotive evolution as yet, most DIY car owners have to rely on the handheld / smartphone diagnostics to scan their cars. 

Be that as it may. Very fortunately there are some common fault lists that would prevent you from having to go buy an expensive OBD-II scanner or go through the agony and trauma of having your car fixed by trial and error. Sharing  common automotive problems for the benefit of other, who are bound to experience the exact same problems in the very near future is a godsend.  Same model cars tend to have the same problems as others but invariable and inevitably those components will fail because obsolescence was part of its initial design. The same components used different model cars tend to fail in the same way and cause the same problems.

We've found that the most common OBD-II problems are associated with misfiring engine cylinders, problematic exhaust Gate Reticulation system (EGR), Oxygen Sensor (O2), Electrical Harnesses and fault Catalytic Converters. Many car owners are decating their diesel models, claiming better performance. But since OBD-II was explicitly introduced to control and reduce carbon emissions, removing it is not such a great idea. 

VW / Audi Harness ES#: ES2993475  

 

COMMON FAULTS 

Erratically idling, or misfiring of bucking or  car goes into limp mode or starts and cuts out all result any one or more of the following error codes:-

P0105 - Manifold Absolute Pressure / Barometric Pressure Voltage supply

P0106 - Manifold Absolute Pressure / Barometric Pressure out of range 

P0107 - Manifold Absolute Pressure / Barometric Pressure Low Input

P0108 - Manifold Absolute Pressure / Barometric Pressure High Input

P0234 - Turbocharger Overboost Condition Control limit exceeded

P0235 - Turbocharger Boost Sensor (A) Control circuit  limit not reached

P0236 - Turbocharger Boost Sensor (A) circuit  out of range

P0237 - Turbocharger Boost Sensor (A) circuit  Low Input

P0238 - Turbocharger Boost Sensor (A) circuit  High Input

P0243 - Turbocharger Wastegate Solenoid (A) Open/Short Circuit to Ground

P0245 - Turbocharger Wastegate Solenoid (A) Low Input/Short to ground

P0246 - Turbocharger Wastegate Solenoid (A) High Input/Short to B+

P1154 - Manifold Switch Over Malfunction

P1155 - Manifold Absolute Pressure Sensor Circuit Short to B+

P1156 - Manifold Absolute Pressure Sensor Circuit Open/Short to Ground

P1157 - Manifold Absolute Pressure Sensor Circuit Power Supply Malfunction

P1158 - Manifold Absolute Pressure Sensor Circuit  out of range

P1400 - EGR Valve Circuit  Electrical Malfunction

P1401 - EGR Valve Circuit  Short to Ground

P1402 - EGR Valve Circuit  Short to B+

P1403 - EGR Flow Deviation

P1404 - EGR Flow Basic Setting not carried out

P1406 - EGR Temperature Sensor Performance range

P1407 - EGR Temperature Sensor Signal too Low

P1408 - EGR Temperature Sensor Signal too High

P1511 - Intake Manifold Changeover Valve - Electrical circuit malfunction

P1512 - Intake Manifold Changeover Valve Short circuit to B+

P1513 - Intake Manifold Changeover Valve2 Short circuit to B+

P1514 - Intake Manifold Changeover Valve2 Short circuit to ground

P1515 - Intake Manifold Changeover Valve Short circuit to ground

P1516 - Intake Manifold Changeover Valve - Open circuit 

P1520 - Intake Manifold Changeover Valve2 - Open circuit 

P1521 - Intake Manifold Changeover Valve2 electrical circuit malfunction

P1553 - Barometric/manifold pressure signal ratio out of range

Polo Highline 1.9 TDI (9N) 2005

16621 - Manifold Pressure / Boost Sensor (G31): Signal too Low

P0237 - 000 - -

Audi A5 (8T0) 2012 

4166 - Manifold Pressure / Boost Sensor (G31)

P0238 00 [039] - Signal too High

Audi TT 1.8L R4/5VT 

16622 - Manifold Pressure / Boost Sensor (G31): Signal too High

0238 - 35-00 - 

000568 - Manifold Pressure / Boost Sensor (G31): Signal too High

P0238 - 001 - Upper Limit Exceeded - MIL ON

Passat 2.0T R4/4V TFSI 2006 

000568 - Manifold Pressure / Boost Sensor (G31): Signal too High

P0238 - 001 - Upper Limit Exceeded - MIL ON

VW Touran 1.9 TDI

P0236 - Manifold Pressure/Boost Sensor (G31) - Range/Performance Problem/Implausible Signal

Malfunction Indicator Lamp (MIL)(K83) active.

VW Golf 7 1.6TDI 

16622 (P0238 ) - Manifold Pressure/Boost Sensor (G31): Signal too High

16618 (P0234) - Boost Pressure Regulation: Limit Exceeded (Overboost Condition)

Passat 2.0T R4/4V TFSI 2006 

004759 - Pressure Drop between Turbo and Throttle Valve

P1297 - 001 - Upper Limit Exceeded

This MAP Manifold Pressure Sensor aka Boost Sensor aka Thrust sensor  aka G31 is just a  thermistor. Essentially a resistor of a special kind, with the ability to change its resistance  subject to its surrounding temperature, hence the term thermistor is just a  word combination of "thermal" and "resistor".  However G31 sensor may not be fault but rather the wiring harness. Due to the constant engine heat, the harness wiring gets hard and becomes brittle resulting in poor contact, short and open circuits. 

FYI - Thermistors essentially come in two varieties, viz NTC (negative temperature coefficient) and a PTC (positive temperature coefficient). You can quite simply use an ohmmeter to measure the resistance of the thermistor. Then by bringing a hot soldering iron  tip close to the thermistor, its resistance would change in response to the soldering iron's radiated heat. When the resistance increases its a PTC and an NTC when the resistance decreases.  Much like discrete component resistors that are colour coded, thermistors leads are also colour coded which identifies the temperature range they operate at.

CATALYTIC CONVERTER

Catalytic Converter have become a hot topic of late. Thieves are stealing Catalytic converters from parked cars at night. However the Polo Highline 1.9 TDI is known to be troublesome. The main reason for  this being, use of poor quality diesel (500ppm as opposed to 50ppm or even 5ppm) and irregular oil changes  which caused soot build-up to block the performance of the catalytic converter, which in turn may lead to turbo failure.  So its fair to say that it's  not uncommon to remove/replace blocked catalytic converters  to prolong the life of the turbo itself.

However if it's not the Catalytic converter itself causing the above error,  it very possibly not the sensor either even though the diagnostic software may indicate that.  I'd say rather check, repair or replace the wiring harness to the Boost Pressure Sensor (G31) and also check wiring to the Intake Air Temperature Sensor (G42).  See my previous blog post https://volkswagen-polo-highline.blogspot.com/2015/03/wiring-harness-issues.html 

The diagnostic scanners may also thow the following errors in conjunction with the error above,  which could be caused by a leak in Air Intake and or Exhaust

16490 - Manifold / Barometric Pressure Sensor (G71) / (F96): Implausible Signal

P0106 - 35-00 - -

18000 - Altitude Sensor / Boost Pressure Sensor: Implausible Correlation

P1592 - 000 - -

Diesel engines are quite different from petrol engines in the sense that  the diesel engine is not variable in speed or power by controlling the air entering the engine as we do with the  throttle body in petrol styled engines. Feedback from Catalytic converter in petrol engines are also used to adjust the short term and long term fuel trim. Implying that petrol cars also have turbo boost errors due to the cat and intake and exhaust sensors.

16485 / P0101 Mass Air Flow Sensor (MAF) (G70) = Circuit Signal Implausible (out of range)

16497 / P0113 Intake Air Temperature  Sensor-1 (G42) = Signal too High

16515 / P0131 O2 (Lambda) sensor low voltage =  Bank-1 Low Voltage

16584 / P0200 Injector circuit =   Injector Circuit electrical fault

16620 / P0236 Turbo / Manifold Pressure Boost Sensor (G31) = Signal Implausible (out of range)

16622 / P0238 Turbo / Manifold Pressure Boost Sensor (G31) = Signal too High

16683 / P0299 Turbo Boost Pressure Reg = Control Range not reached (underboost) /mechanical fault

16785 / P0401 Exhaust Gas Recirculation (EGR) = Insufficient Flow (blocked)

17055 / P0671  Glow Plug/Heater Cylinder 1 (Q10)  electrical fault, open circuit 

17958 / P1550 code = Charge Pressure Control Deviation

Check for air leaks on both intake or exhaust side 

Turbocharger - check for whining engine and exhaust smoke

Charge Air Pressure Sensor faulty  - check connection to one of the the intercooler pipes

Wastegate Regulator N75 Valve  faulty  - Check one of the 3 thin hoses for leaks

18534 / P2102 Throttle  Actuator Control Motor = Signal too Low, check voltage to accelerator pedal 

18675 / P2243 O2  Sensor Reference Voltage Bank 1, open circuit 

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High Speed Computers

HIGH SPEED COMPUTERS

All modern-day motor vehicles using our roads today; and those manufactured since 1996 can literally be referred to as COW ("computers on wheels"). Since your car is less than 25  years in age, it certainly has a computer on board, but the level of control it has over your car is determined by its recentness.  So the more recent your car the more  control the computer has over its functionality. 

BLACK BOXES

However, the computer in question is unlike the ones with the LCD screen, keyboard and mouse that everyone is familiar with, yet very similar in its processing ability. One  could say these computers are akin to the flight recorders fitted to aircraft which in  avionics are commonly called "black-boxes". But unlike the traditional PC, automotive  "black-boxes" are heavily regulated by standards and legislation regarding consumer  safety. 

ECU

Industry wide automotive "black-boxes" are commonly known as Electronic Control Units abbreviated ECUs and is the home of on-board diagnostics software, named OBD II. This  on-board diagnostic system in essence is a combination of hardware and software  running an intelligent system that incorporates various types of the sensors, each  integrated into the vital areas of the vehicle that monitors its overall performance.The most common of which are the engine RPM sensor, the crankshaft and camshaft  position sensors, the car's air and coolant temperature sensor, the oil level sensor, road speed sensor, the accelerator pedal and throttle control sensor which is also  known as drive-by-wire. The software consists of over 100 million lines of code which pools and controls dozens of electronic control units (ECUs) via the CAN  protocol and CAN bus thus able to manipulate everything from Engine Electronics to ABS braking system, to Steering Assist, to Infotainment System, to Heating/Air  Conditioning, to Airbag, to Instrument Cluster, to Tire Pressure Monitoring, to Back-Up Camera among so many other. 

SENSORS

As such, ECUs have revolutionized and souped-up modern motor vehicles, giving them added fuel efficiency, safety, pollution reduction, speed on demand, and an early  diagnostic malfunction detection. Restated, the ECU contains a self-diagnosis system capable of detecting glitches and small mechanical and electrical issues long before  they actually occur thus saving you thousands in tow-in charges and would be expensive repairs. It eliminates the need to cross the fingers when you start hearing  peculiar noises coming from the engine or transmission and it could prevent you from  getting stuck on the road.

DIAGNOSTIC TROUBLE CODES

Vehicle dependent, the OBD II system alerts the driver to any malfunction in real time by flagging errors by way of digital code, displayed on the dashboard. Decoding these  errors timorously and taking the necessary action would certainly avert more serious troubles later. Errors on vehicles without LCD display can be viewed with a diagnostic  scan tool when plugged into its 16-pin ODB II socket. These vehicles would then also have CEL (check engine light) / aka MIL (malfunction indicator lamp, an EPC light among  its menagerie of symbol warning lights. DTC (diagnostic trouble codes) are  essentially fault codes, presented as five-digit alphanumeric codes that identify a particular problem in one of four areas in the car, viz: P-Codes (Power train), U-Codes  (Chassis), B-Codes (Body) and U-Codes (User Wiring Bus Network). 

A few example of these codes are P0195 - Engine Oil Temperature Sensor, P0304 -  Cylinder 4 Misfire  Detected, B1000 - ECU Malfunction, B1713 - Mirror Switch R Down Input Stuck High, C0050 - Right Rear Wheel Speed Circuit Malfunction, C0611 - VIN Information Error,  U0130 Lost Communication With Steering Effort Control Module and U0324 Software Incompatibility with HVAC Control Module. Without a scan tool plugged into the OBD II  socket it’s impossible to extract the DTC from the ECU non-volatile memory, let alone  fix these faults.

ODB II SOCKET

It would therefore be fair to say that the OBD II socket has become the most important and indispensable means of diagnosing automotive problems hence also fair to say that  it has become the most used automotive receptacle since its inception. That being said, OBD II GPS tracker is now also the most convenient vehicle tracking device on  the market via GSM which plugs into a splitter / adapter cable. Armed with a SIM card, the GPS GSM module can be tracked on a cell phone tracking app and the software would even  allow its user to disable the car’s engine remotely via GSM /GPRS and OBD II in the event the vehicle is hijacked or stolen. Unlike GSM where the cost of a data call is  related to the time spent on the network, a GPRS data session is dependent on the amount of data sent and received. So by implication GPRS is “always on always  connected”. 

GPS MODULE

GPS modules generally have several convenient features amongst which is a real-time vehicle tracking system with a 180-day of tracking historical data accessible on a web  server. GPS has time accuracy of 1 microsecond and an accuracy of less than 10 meters. It will continue working even if the cars battery is removed as it has a built-in  180mAh/ 3.7V battery. GSM module also has a host of security features but the best  part of an OBD II GPS Tracker is that it's simple to install without any wire  connections. It is purely a DIY matter of plug and play. A splitter cable that plugs  into the cars original 16-pin OBD II port with two addition 16-pin OBD II ports, one for the GPS module and the other available to a scan tool. 

SECURITY RISKS

All this fancy gadgetry doesn't come with risks. The first of which is the CAN  protocol which suffers from several security issues that were originally ignored by  most vehicles manufactures. Reason being that the various automotive networks and  ECUs were initially designed to primarily gain physical access to the vehicle ECUs and speed / reaction-time was a secondary concern and more important that security which  was then placed on the back burner. With a GSM SIM card in the GPS module that can directly  communicate with the CAN bus and protocol it wouldn't be difficult for a hacker to gain access to the vehicle as it will be just another node on the internet. With remote interfaces like Wi-Fi, Bluetooth, or cellular that is accessible from  outside of the car, access can typically be gained, thus aftermarket OBD-II devices have the potential to introduce security risks to an automobile and compromise the safety of its passengers. Connecting directly to the vehicle in this manner could result in control over safety-critical functions as CAN, by design, offers no  protection from hacker manipulation.

With none existent comms security, somehow cars of the future with a CAN-Bus at its basis doesn't look it has a future at all. It reminds of other technologies that we were forced to abandon with the arrival of the new. Case in point, Vinyl Records for CD recorders, DVD that superseded video tapes, MP3 players that superseded audio cassettes and audio CD's, Flash drives that superseded removable media, etc. Solid state drives that is superseding hard drives. Would we have to abandon our CAN based cars like we did our other techno bits in favour of a new automotive protocols with features that has support for Kerberos, SSH, IPSec, OSPF authentication, VPNs, SSL and TLS?

Limp Mode Scan codes

LIMP MODE

Limp mode has hit car owners like a pandemic, a pandemic that was pre-planned by the automotive industry, knowing full well that most car owners would be at a loss to repair it themselves and that it was  going to be a source of steady profit, a bonanza, a money spinner, a cash cow, a golden goose for them.

Virtually every car owner have experienced the wrath of Limp mode at some time or the other and are often helpless when it happens. Those of you who haven't had the displeasure of encountering Limp mod surely will, its just a matter of time - virtually guaranteed.

STANDARD FEATURE

Limp mode is a standard feature programmed into all post-1996 vehicles to protect their engines and driver / passenger when something goes awry with its EPC system, steering or braking system, etc.  The ever-aware sensing software will activate this feature when it detects abnormal readings from sensors, or compromised mechanical part operations that could potentially cause damage to the vehicle or harm to its occupants.

Every time when Limp mode is triggered the ECU will store a DTC in its non-volatile memory for later retrieval. And since Limp mode can be caused by any of several different engine components, the only way to track down the Limp mode problem is by way of a OBD-II scan tool. Scan tools may be considered the vaccines against this Limp mode pandemic, implying only those who have one will be able to fix their own cars.

ON BOARD DIAGNOSTICS

OBD-II (on-board diagnostics ver2) gave rise to a scan tool market and these scan tools comes in several makes and models, with capabilities ranging from the most basic to the most intricate costing from as little as a few bucks to tens of thousands. Most of the low end scan tools are VW compatible though some are not, whereas all the high end scan tools are compatible to virtually all cars, trucks and bikes.

SCAN TOOL

So, if your a car owner / DIY mechanic, it is imperative to get yourself a decent  aftermarket VW-Audi diagnostic scan tool. If you own an Audi,  Porsche, Bentley, Bugatti, Lamborghini,  SEAT, Škoda or Volkswagen I would suggest that you invest in the USB Cable KKL 409.1 VAG-COM Auto Scanner Scan Tool for VW/Audi (Blue) for starters. This cable supports the ISO9141 and KWP2000 transmission protocols and is usable with VCDS lite downloadable from the Ross tech website absolutely free. I started out with this rig and later bought several dedicated scan tools as well as bluetooth dongles that work with cellphones and software for my tablet. None as good or even comparable to VCDS (VAG-COM) HEX-V2 which surpasses the performance of most generic OBD-II tools, but its VW specific.

ELECTRONIC POWER CONTROL

Limp mode limits the amount of power to your engine and transmission thus delivers poor engine performance. EPC (electronic power control) may be lit and Malfunction Indicator Lamp (MIL)(K83) may also be lit. 

Limp mode scan codes:-

000289 (P0121) - Throttle Position Sensor (G69): Implausible Signal

000290 (P0122) - Throttle Position Sensor (G69): Signal too Low

004243 (P1093) - Bank 1; Fuel Measuring System 2

000545 (P0221) - Angle Sensor 2 for Throttle (G188): Implausible Signal  

000808 (P0328) - Knock Sensor 1 (G61) Signal too High - Intermittent

05445 (P1545) - Throttle valve control system, Malfunction

05464 (P1558) - EPV throttle Drive - G186, Electrical malfunction in circuit

01314 - Engine control module / No Communications

17252 (P0868) - Transmission Fluid Pressure Adaptation at Limit

             

WIRING HARNESS

As can be seen from the above, all these Limp mode scan codes / faults are associated with a VW wiring  harness problem and is normally a connector problem but it can also be the a failed throttle body, a knock sensor, the torque circuit, a brake light. The gears inside of the throttle body can strip or becomes clogged with dirt. Remember the last resort is a failed engine control unit (ECU).

Electronic Vehicle Architecture

The Electronics  Industry has had the fastest growth in the shortest amount of time, when compared to any other industry worldwide.  But before I expound on that, let me just say that, the invention of numerous mechanical contraptions during the late 1800s, like  James Watt's steam engine for example, started the transition towards new manufacturing processes which collectively gave rise to the Industrial Revolution. Much later Samuel Finley Breese Morse invented the single-wire electric telegraph system and developed the Morse  Code. 

A bit of History

Sometime thereafter Alexander Graham Bell invented the first practical telephone system. Their's and the collective  efforts of so many others, without discounting anyone's  inventions and efforts, changed telecommunications forever. Ancient records show that  the first streets of Baghdad were paved with tar, that the Babylonians used asphalt to construct the walls and towers of Babylon.  The I-Ching even bears testimony to the fact that the cites of China used oil, extracted in its raw state some  2000 years ago before refining was first  discovered. Implying that the petroleum industry is not new, but that the current status of petroleum is a key component of politics,  technology and society today.

No tot digress, tar, crude oil and pitch, were used as a sources of fuel long before paraffin was even distilled from it. The thin distilled  paraffin was normally used as fuel for lamps whereas several hundreds of years later, the thicker residue was used to lubricate machinery. In and around the  time when oil/gas/fuel/petroluem was extracted from coal, Étienne Lenoir successfully built the internal combustion engine and innovated by Nikolaus Otto, who became famous for successfully developing the compressed charge internal combustion engine - the Otto engine.  

Assembly lines

Henry Ford on  the other hand wasn't an inventor nor an innovator as many have been led to believe, but he was rather a business magnate and a captain of  industry, who formed the Ford Motor Company, and sponsored the development of the "assembly line technique" for vehicle mass  production. One can therefore confidently say that their combined efforts, without diminishing any other contributor's efforts by the very least, over a period of some 200 years, are partially responsible for the social changes and economic development that shaped  societies that we live in today. This was  the infancy of the Automotive industry.

However, compared the Industrial revolution, modern day electronics would be equivalent to a Global Coup. Initially there was the  vacuum tube aka the electron tube, colloquially known as a valve. It gave way to the trusty transistor and discrete components which gave rise to the  analogue Integrated Circuit (IC) aka chip, followed by digital Transistor/Transistor logic (TTL) chips, followed by complementary  metal oxide semiconductors (CMOS), then digital semiconductors like ROM (digital read only memory), RAM (random access memory),  EEPROM (electronically erasable programmable read only memory), followed by large scale integration chips and VSLI (Very Large Scale  Integration Chips). 

Electronics and Software

With the advent of multilayer circuit boards and surface mounted technology, microcontroller SoC (system on a chip)  and microprocessors (µP) became pervasive. Assembler language was superseded by several high level languages for programmable chips and  software programming sat at the heart of most electronic devices and electronic systems. All of this happened in 50 years of electronics  as opposed  to 200 years of mechanical devices.

So you may ask, what has all this history to do with Volkswagen, Audi, Seat and Skoda and for that matter all other modes of transport  from plans to trains? Well the short answer, everything! Much like the Industrial Revolution with its mechanical ingenuity;  cars and planes were also predominantly mechanical since its inception, its mechanical ignition system was prone to imprecise ignition timing, resulting in improper fuel mixture burn, thus increasing its exhaust pollution. 

With the rise of telecommunications, so did  the electric wires, and electrically controlled gauges, relays and switches in cars and planes multiplied. The ever inflating cost of  gasoline then triggered the invention of CDI (Capacitive Discharge Ignition systems) which is in fact the first type of electronic  contraption integrated into the ignition system of a vehicle in order to, more precisely control its ignition timing, making it more  fuel efficient. 

These devices were available as add on kits and not produced as standard equipment in cars at the time. The preferred standard  equipment was the IDI  (inductive ignition system) and is the most common ignition system found on all cars built prior to 1980. It used a coil and distributor incorporating breaker points in its ignition system that was prone to ware-out due to arcing on  contact. During the 80's engines still used a coil and distributor to achieve dwell but it was somewhat computer controlled and by  the 90's the automotive computer evolved to ignition modules and the ECU, replacing the coil with a power pack. 

However, with the constant and  ever increasing price of gasoline and looming environmental concerns centred around vehicle exhaust pollution, the automotive  industry then accelerated its research and development into newer more compact fuel efficient power-train systems capable of higher  power output with enhanced robustness with a open policy towards alternative fuels.

New generation cars

So, by the 90's the Insulated-Gate Bipolar Transistor (IGBT) was introduced into the ignition system as discrete component connected  to the ECU called OBD - On-Board diagnostics. By 1993 the CAN protocol was standardized by ISO which led to its increased popularity  and adoption across the automotive industry.  By 1996 OBD had evolved to OBD-II and the discrete IGBT evolve into a IGBT module  integrated into individual coils itself. Starting from Y2k ignition systems were all ECU based but power packs were replaced by a  dedicated coil per cylinder, yet cloning the use of an Insulated-Gate Bipolar Transistor (IGBT) as discrete component connected to  the ECU. 

Communication Buses

From 2004 to 2010 the discrete Insulated-Gate Bipolar Transistor (IGBT) integrated into individual ignition coils evolved to a smart IGBT alongside the ECU.  The automotive ignition system had undergone a complete revolution which contributed significantly  to the system’s efficiency, exhaust pollution reduction, and robustness. By which time the use of wires had been minimized in  preference of a bus network which supported vehicle weight reduction and  vehicle cost. Copper wire have been replaced by fibre optic cable to facilitate faster communication. Some of the most important bus communication systems are CAN-Bus, Lin-Bus, MOST and  FlexRay.

Actuators and sensors, electronic control modules, Can-Bus and the ECU collectively facilitating Electronic Power Control (EPC) aka electronic throttle  control (ETC), Electronic Exhaust gas reticulation (EEGR), Electronic Valve Control (EVC), Electronic fuel injectors and so much  more, are just a small part of the overall influence that electronics have had on all vehicle engines. Other subsidiary programmable electronic  modules which are smaller computers in their own right now permeate cars, bikes, planes and boats, all connected together by at least three network systems. 

CAN-Bus is a multi-master twisted pair wire system reserved for high speed control systems like brakes,  whereas LIN bus is a single master, single wire system for low level communication for use by the rain sensor, sun roof, internal heating, and  the infotainment-bus, is a slow-speed system reserved for radio, GPS, internet communication, etc. Each system communicating with each  of its nodes in its provided protocol, each having different data transmission rates. By incorporating this level of electronics into cars, it has vastly improved stichometry and overall engine  performance, its economy, its driveability  and its safety besides reducing  emissions. 

Inept electronic knowledge

However, few mechanics know sufficient about electronics with its combinational logic, digital multiplexing, bits and  bytes, start and stop bits, fixed frames, software, etc to repair these cars packed with intercommunicating electronic modules. Even though scan tools have vastly increased their chances at successful repair, not knowing how to interpret fault codes further disadvantages them, not to  mention how frustrating it is for the vehicle owner who gets stuff around by incompetence. And here I’m even refereeing to the  "Automotive Technicians" employed by their respective automotive agents, who are more often than not incapable of repairing vehicles fitted with OBD-II. I'm quite sure there are several hundred if not thousands  of  VW owners who would concur.  How is it even expected for the DIY mechanic to fix it him or her self if the agents can't. Needless to say that  with continuous improvements comes great complexity and their successful  strategy to part us with our hard earned monies.

Diagnostic Trouble Codes abbreviated as DTC have been around for approx 30 years and is a component of OBD-II (onboard diagnostic system ver.2). These codes can be found stored  in the ECU's non-volatile memory for later retrieval by way of a scan tool. DTCs are displayed specific to the kind of problem that the system can or does detect from inside of a car engine/transmission, chassis, body or network.

Scan codes

In reality DTC codes can assist "automotive technicians", DIY mechanics and car owners to understand the problem with the car and possibly point them towards the nature of the problem or at the very least the system concerned. Bearing in mind many DTCs are generic but many of them are manufacturer specific and is best interpreted by consulting the car's manual.  Generic codes are defined by the EOBD / OBD-II standard and will therefore be the same for all car manufacturers.

But, let me break it down to for you. All diagnostic codes are alphanumeric as in P0XXX. It start with a letter followed by 4 numbers, as in P0303. This initial letter is P but can also be either B, C or U. They stand for Powertrain, Body, Chassis and Network respectively. The first numeral following the letter signifies whether the fault is generic of manufacturer specific. Since its a 0, its a generic code but if had a 1 then it would be manufacturer specific. The number 3  following the first 0 can be any numeral between 1 and 9. This number directs you to the subsystem of the car and is as follows.

Px1xx Air and fuel metering

Px2xx Air and fuel metering

Px3xx Ignition system and misfires

Px4xx Auxiliary  / additional emission control

Px5xx Speed control and idle regulation

Px6xx Communication /computer output signals

Px7xx Transmission

Px8xx Transmission

Px9xx Control modules, input and output signals

The final two numbers (xx) designate the individual components / sensors /actuator that threw the error. For example P0300 says, it's a powertrain error, it's generic in nature, it's in the ignition system and it's a random misfire. 

Whereas P0301 says misfire by cylinder No. 1,

Whereas P0304 says misfire by cylinder No. 4,

Whereas P0308 says misfire by cylinder No. 8,

Whereas P0312 says misfire by cylinder No. 12,

Likewise P0403 says, its a powetrain error, it's generic in nature, it's in the auxiliary / emission system and that the "Exhaust gas recirculation control malfunctioned"

Likewise P0501 says, its a powetrain error, it's generic in nature, it's in the speed control/regulation circuit and it's the "Vehicle speed sensor is out of range".

Like wise P0656 says,its a powetrain error, it's generic in nature, its in the computer/communication system and that its the "Fuel level output electrical sensor/circuit" 

Then there are also VAG specific 5 number numerical codes that coincide with P,B,C and U codes, like 16692 which coincides with P0308 (Misfire Detected on Cylinder 8)

And 17026 which coincides with P0642 (Knock Control Control Module Malfunction)

VOLKSWAGEN HACK

VOLKSWAGEN  HACK

Since the inception of OBD-II car manufacturers were mandated to install immobilizers on all vehicles built from 1996 onward. The preferred technology used by more than a dozen vehicle manufactures which includes Audi, Volkswagen, Volvo, Fiat, Honda and Chevrolet, was the Magamos Cryto transponder, viz ID48. A passive glass RFID chip used for authentication and preventing hot-wiring, embedded in the keys of these vehicles had a vulnerability. Electronic vehicle immobilizers in general have been very effective at reducing car theft to date, but today some 24 years later virtually each and every car immobilizer manufactured is defunct and the security they provide is worthless because its been hacked. 

This vulnerability in automotive security was cracked as long ago as 2013 by computer scientist Flavio Garcia and a team of researchers at the University of Birmingham. By implication they suddenly had access to a 100 000 000 Volkswagen vehicles across the globe. However, before they could publish their research to general public consumption, they were hit with a lawsuit which caused a two year delay but their paper was eventually publisized.  Their article reveals numerous weaknesses in the design of the cipher, the authentication protocol and also in its implementation allowing them to gain eavesdrop on authentication traces. This was sufficient  to recover the 96-bit secret key with a computational complexity of 256 cipher ticks and the secret key after 3 × 216 authentication attempts. This was all achievable in under  only 30 minutes. 

This all came about when local police was baffled that cars were being stolen and nobody could explain how. But they suspected that the thieves  used some kind of ‘car diagnostic’ device to bypass the immobilizer and start a car without a genuine key. In order to solve this mystery Flavio Garci and his researchers  were motivated to evaluate the security of vehicle immobilizer transponders. At the time it was commonly known hack attacks for other widely used immobilizer transponders, viz DST40, Keeloq and Hitag2 though  not much was known about the vulnerabilities of the Megamos Crypto transponder.

The Megamos Crypto transponder has since been cracked by the university team in their attempt to discover how "the thieves did it'' and realized how easy it was. This speak volumes about the technical, cryptographic, algorthmic, code cracking software savviness of the thieve who figured it all out even before the scientist and his team.

So now a team of researchers from the University of Birmingham and a German engineering company viz. Kasper & Oswald intent revealing two distinct vulnerabilities they say affect keyless entry systems. Using these two vulnerabilities resourceful thieves would be able to wirelessly unlock virtually every vehicle that  Volkswagen manufactured during the past twenty years.  These include  cars from manufacturers like Alfa Romeo, Citroen, Fiat, Ford, Mitsubishi, Nissan, Opel, and Peugeot. 

No car with the most sophisticated immobilizer built during this time is immune to evaporate in the middle of the night, unless protected by old school brute force, steering and gear locks, parked inside a garage protected by half a dozen pitbulls.

FOB key

FOB key Tips and Tricks

With the advent of electronics, life for many has become somewhat easier and high-tech. Case in point, the trusty television cordless infrared remote control and its earlier ultrasonic equivalents. Both circumventing the "jack in a box" activity we all so enjoyed, during the days of legacy non-remote control television sets. Likewise, our cars has also gone high-tech, flaunting electronic car key remote controls with features never seen before. No longer using infra-red or ultrasonic but a coded signal modulated in a wireless radio frequency in the 315 to 434 mhz range.  

Not only has remote controls replaced the aim push and turn function our writs won't forget but has gone far beyond locking or unlocking doors, remotely starting the car,  emitting chirping sounds with flashing hazards to assist us to find our car in a fully populated parking lot. These fancy electronic remotes control marvels are referred to as a "fob", an acronym for Frequency Operated Button. In a previous lifetime, a "fob" was the name given to the chain connecting a packet watch to its owner. Today the "fob" is form of invisible tether, chaining the remote to the car. Some say the word "fob" comes from the German word Fuppe, meaning pocket. I suppose that's where its going live when its not on the car. 

Manufacturers are constantly adding more features to the already multitude of functions that make both the car and the key "fob"  more useful than ever before. But its not all done in the name of the client. It has allowed manufacturers skimp of a few items that drove the price of the car up ever so slightly. Fobs allowed them to only install a single driver-door key cylinder, thereby saving on the cost of the other three, the installation time and somewhat reduced the weight of the car, alongside so many other items.  Collectively contributing to its overall fuel economy. But the quality of this driver's door cylinder isn't design nor manufactured robust enough and daily use. It's intended for emergencies only use, when the key is either locked inside the car or the battery had died of the "fob"  has gone faulty. Using it daily will kill that lock before you can fluently say, Rumplestillhurrywisepunywalgeemuckagee.

VW button mechanically operated switch blade "fob" comes in 2 basic flavours -- 2 button and 3 button.  One buttons specifically  for lock and the other for unlock. Keeping the button depress for a few seconds activates windows either open or close whichever is needed.  A flashing LED on the remote denotes communication.
Depending on the ECU/ control module settings, button depresses can be either audible or visible or both. Meaning a peep or two from the hooter and single or double flashing of the hazard light, or nothing based on personal preferences.  In the case of a 3 button, much like the 2 it just has a 3 for trunk release. In those vehicles with an auto lift trunk piston feature, pressing the unlock button will is open the trunk completely. 

The "fob" is a sophisticated piece of equipment but when it misbehaves, and you have to make multiple attempts before it performs a function, it could be that the battery is going flat. This is easily verified by viewing the intensity of the blinking LED on the "fob". A faint LED is a tell tail sign the the battery is giving up the ghost. When the battery is replaced, the "fob" needs to be reset. This can be done by pressing the lock one second while the car is locked. Nothing will happen except perhaps a low volume yet mechanical clunk. Remove the cylinder cover, unlock and re-lock your your car with the master-key, not spare key. This action will cause your "fob" to reset itself.

When the car wont start and the light is flashing the key, keep it close to start button to make reading the key easier so that the car will start. VW Tiquan and some other later VW's allows  "fob"  synchronization and reprogramming of driver preference like, radio stations, mirror positions, etc.  Since a detailed rundown of the procedures are beyond the scope of this post, your owners' manual is by far your best bet. 

EPC issues

EPC Issues

EPC complaints have become the most common Volkswagen fault and outstrips check-engine-light three to one. It is one of the most tiresome and frustrating  faults to diagnose and repair because the only way of knowing that your most recent repair cured your EPC problem, is when it does't occur in the same situation under the same conditions thereafter. Mechanisms generally refer to Electronic Power Control (EPC) faults as evil, a waste of time and the cause of embarrassment.

Many disillusioned VW car owners can confirm that they've taken their vehicle to at least 2 different workshops to fix their respective EPC light problem. Often wanting a refund from the first workshop as they didn't fix the EPC issue, but only said they did. It's also known fact that tons of spare parts suspected of causing EPC have been replaced that didn't need replacing in the first place. Trial and error EPC repair seems to be the order of the day among motor mechanics. Even the agents are guilty of this and VW car owners are generally fed-up of mechanical and electronic competence. Many car owners and DIY mechanics are longing for the days when cars had a lot less electronics, were easier to diagnose and repair and one didn't need a degree in automotive engineering to replace something as meager as a MAF sensor. The word EPC among many others, is just one of the mechanical jargon that has come to invade the car industry. There are so many; to list just a few. Several of them capable of throwing an EPC light.

AIR: Air Injection System
ACC: Adaptive Cruise Control
ABS: Antilock Braking System
AWD: All-Wheel Drive
BHP: Brake Horsepower
CEL: Check Engine Light
CO2: Carbon Dioxide
CKP: Crankshaft Position Sensor
DLC: Data Link Connector
DDI: Direct Diesel Injection
DPF: Diesel Particulate Filter
DRL: Daytime Running Lights
DTC: Diagnostic Trouble Codes 
DSG: Direct-Shift Gearbox
ECT: Engine Coolant Temperature
ECU: Electronic Control Unit
EGR: Exhaust Gas Recirculation
EPA: Environmental Protection Agency
ESC: Electronic Stability Control
ESP: Electronic Stability Program 
FSH: Full Service History
FWD: Front Wheel Drive
IAT: Intake Air Temperature
KPH: Kilometres Per Hour
LED: Light Emitting Diode
LSD: Limited Slip Differential
LPG: Liquid Petroleum Gas
LWB: Long Wheelbase
MAF : Mass Air Flow (sensor) 
MAP: Manifold Absolute Pressure
MIL: Malfunction Indicator Light
MPV: Multi-Purpose Vehicle 
OBD: On-board Diagnostics
PCM: Powertrain Control Module
RPM: Revolutions Per Minute
RWD: Rear Wheel Drive
SUV: Sport Utility Vehicle
TDC: Top Dead Center
TCS: Traction Control System
TCU: Transmission Control Unit
TPS: Throttle Position Sensor
VCM: Vehicle Communications Module 
VIN: Vehicle Identification Number
VRM: Vehicle Registration Mark
WOT: Wide Open Throttle

The letters EPC in the automotive sector initially meant Electronic Parts Catalogue. Recording every conceivable component used in the  manufacture of that car, listed in alphanumeric order. Some EPC are exclusively online versions, or downloadable as pdf. Some cover specific cars  and others cover several makes of cars and is normally free, whereas the more elaborate EPCs with specialist automotive service data is charged for per search or as a monthly subscription.

For example, the ETK 2018 EPC  is specific to BMW,  Rolls Royce, Mini and the Chinese Zinoro which is the luxury automobile brand owned by BMW Brilliance specializing  in electric vehicles. ETK comes at an exorbitant price, in either downloadable or CD/DVD form. The Volkswagen  ETKA online /  ELSAWIN EPC is specific to Volkswagen, Audi, Seat and Skoda and spans 6 CDs and is also fairly expensive. It is an encyclopediac like compendium covering VW, Audi, Seat and Skoda vehicles manufactured between 1947 and 2018 in varying degrees of detail. 

It also includes the actual service & repair software used by factory technicians at Volkswagen, Audi, Seat, Skoda and their dealer workshops throughout the world. As such it would be in indispensable resource for the Volkswagen enthusiast but is also overkill for most. However most modern day cars have an EPC circuit which essentially deals with the torque of the vehicle. Using one of these catalogues and its diagnostic diagrams to identify these components and problems is one of the easiest ways of fixing EPC problems. To fix your EPC problem, click here, here or here.

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VW Beginings

VW's humble beginings

Volkswagen, derived from the German words "Folk's Wagon" or "People's Wagon," traces its roots back to 1937 when it was founded as a pivotal player in the automotive industry. Over the decades, it has grown into the largest car manufacturer globally, boasting an extensive lineup of vehicles. One of its most iconic creations is the Volkswagen Beetle, which has left an indelible mark on automotive history.

VW Beetle 1937

Commissioned by Adolf Hitler, the leader of Nazi Germany, the Volkswagen Beetle was conceptualized and designed by Ferdinand Porsche, the renowned Austrian-German automotive engineer and founder of the Porsche car company. 

The Beetle first rolled off the production lines in Germany in 1937 and remained in production until the late 1970s. However, its legacy endured, with production continuing at Volkswagen's Puebla facility in Mexico until 2003. In total, over 21 million Beetles were manufactured, earning it the affectionate moniker of the "poor man's Porsche."

The Beetle's success paved the way for other Volkswagen models, including the Type 2, famously known as the VW 'Bus' or Microbus, and the stylish Karmann Ghia. Subsequent iterations, such as the Type 3 'Ponton' and the Type 4 411/412 family car, further solidified Volkswagen's reputation for innovation and versatility in the automotive market.

Despite its iconic status, Volkswagen eventually ceased production of the Beetle, citing feasibility concerns in an increasingly competitive market. As other car manufacturers introduced similar-sized four-door vehicles, the Beetle, Karmann Ghia, and 'Ponton,' all two-door models, faced challenges in meeting the evolving needs of consumers, particularly in the taxi industry. The practicality of four-door vehicles for passenger transportation outweighed the convenience of two-door models, leading to a shift in consumer preferences.

This transition marked a pivotal moment in Volkswagen's history, reflecting the company's adaptability to changing market dynamics while staying true to its commitment to innovation and excellence in automotive engineering. While the Beetle era may have drawn to a close, its legacy lives on, serving as a testament to Volkswagen's enduring impact on the automotive landscape.

 The New Beetle was manufactured from 1998–2011 which included  a 2-door coupé/ convertible but wasn’t  a replacement for the original Beetle,  the VW golf and VW Passat was.  The original Beetle, the VW Golf  and the VW Passat were the three top VW cars in the history of the automaker, all three of which stood out for its simplicity, affordability and quality for more than thirty years.  The Volkswagen Beetle  is a two-door economy car, intended for five occupants  and sported an air-cooled rear mounted engine.

VW Fuses Switches and Relays

VW Fuses  Switches and Relays

Single Pole Single Throw

Electrical switches comes in several configurations, but are normally classified into only four types. The most common switch is the single pole single throw, abbreviated as SPST. This implies it has one contact that is normally open —abbreviated N/O—  which is closed when the switch is flicked. This type of switch is either on-or-off / open circuit or closed circuit. This switch also comes in the form of a push button switch which is normally open and closes when pushed but when released it open once again. It is also known as push-to-make, abbreviated PTM. An example of a PTM is a door bell switch or a cars hooter or the individual keys on a keyboard. Push button switches also comes in a normally closed configuration and opens when pushed, but when released, it closes again. Commonly  known as push-to-break, abbreviated PTB. An example of a PTB switch is used to release a door, held closed by an electromagnet.

Suzuki GS500 GSXR1100, Honda  VT 500 VT600 VT700 VF750,
Kawasaki ZX1000 ZX 1100 Solenoid

Single Pole Double Throw

The second and slightly more advanced switch is the single pole double throw switch, abbreviated as SPDT. This is a three terminal switch which toggles between two states when switched. SPDT are in essence two switches in one package. The one switch is normally open whilst the other is normally closed. By flicking the switch the two switches reverses their roles. The normally open switch is then closed and the normally close switch is opened. By connecting a SPDT at either end of a long passage to turns the lights or off, one is able to enter the passage at one end, turn the lights on and when exiting the passage at the other end switch the lights off. SPDT can be used as a SPST in an application by just using the centre contact and either one of the other two contacts, depending on what type of switch you need, N/O or N/C.  SPDT switches are also available with a centre-off position, known as momentary (ON)-OFF-(ON) switch.

Volkswagen 4H0951253 Starter Relay 645 and 1J0906381A Fuel pump relay 109. 

Double Pole Single Trow

The third type of switch is the DPST and is similar to the SPST switch in operation except that it has a pair of on-off switches that switch together. It is commonly used to connect / interrupt both the live and neutral supplies in a circuit simultaneously or it may be used to switch two separate circuits simultaneously. Computer power supplies have DPDT switches as a safety feature to avoid getting electrocuted whilst working on the power supply if only one pole was switched. 

Double Pole Double Throw

The fourth type of switch is the DPDT and is similar to the SPDT switch in operation except that it has a pair of on-on switches that switch together. It is commonly wired to reverse the direction of a DC motor or be used to switch between to different colour LEDS. DPDT can be used as a DPSP in an application by using the centre contact and either one of the other two contacts and duplicated on the paired switch. DPDP switches are also available with a centre-off position, known as momentary (ON)-OFF-(ON) switch.

Switches 

Switches switches come in various shapes among which are Toggle switches, limit switches, reed switches, micro switches, mercury switches, rotary switch, slide switch, rocker switch, pneumatic limit switches, selector switches and getting the right switch for the job cam sometimes be tricky and may be better suited by using a relay. Many switches also come with a rubber jacket to make it  waterproof. However that doesn't imply you can submerse the switch in water, it is more a splash proof cover than a water proof one. There are switches suited for using under water, for example a floating mercury switch. when a vat or tank is filled with liquid, the switch would float in the upright position but when the liquid falls below a certain lever  the switch would float upside down and trigger. Perhaps turning on a pump that would fill the tank or vat once again.

Whats a relay?

Having discussed switches you may ask what does switches have to do with relays. The simple answer is, a relay is essentially a remotely controlled switch. Relays are controlled electrically rather than mechanically, hence they're known as electro-mechanical relays. They are commonly used in automotive design, where high current devices can be switched from a cockpit fairly cheaply. In stead of using long lengths of thick high current cable and a substantially heavy duty on-off switch to control a heater or a motor situated some distance from the driver; a small low current switch and a length of thin low current cable and a relay switch with heavy contacts would suffice. Every relays has a solenoid configured as an electromagnet. So when the solenoid is activated by a trigger voltage, the electromagnet pulls a set of heavy duty contacts to make or break a circuit. Relays are versatile and can function as a simple spst switch, or a more advance spdt switch of a dpst switch or a dpdt switch depending on the circuity it needs to control.

Volkswagen Solenoids

Sometimes you may need a switch with more contacts than the best switch you can find, and this is where relays outweigh switches. Relays also cost less than the combines cost of all the switches that it replaces or that can do the job of.  Volkswagen have several relays throughout its electrical system and the most hardworking relay, is the starter relay.  Starter relays form part of the starter, the reasoning, is to keep high current conductors as short as possible. However many cars have a second relay inserted into the fuse panel that powers the starter solenoid. So when you turn the ignition key to start your car, the starter relay contacts in the fuse box sends 12V to the starter solenoid on the starter. This solenoid's contacts throw and sends 12V from the thick battery cable that's connected to one side of the starter solenoid directly to the starter's field coils, causing its armature  to spin. But at exactly the same time the solenoid performs a dual function as it kicks the bendix forward into the ring gear's teeth.  The starter's force of rotation is sufficient to crack the engine and if all's well, the engine with start. 

Volkswagen

Volkswagen

Volkswagen cars are extremely popular. In fact, they are so  popular that Volkswagen as a brand is the favourite car of many South Africans, besides being the most popular car sold on the South African market. Volkswagen cars are also popular elsewhere and are sold in virtually every country throughout the world; but its popularity and its global acclaimed robustness doesn't make it indestructible. 

Volkswagen cars give problems, in fact they are more troublesome now, than they've ever been. The reason, the ODB-II system with its ever increasing number of ECUs.  This system has several features that means well, like controlling toxic emissions, like giving you the best fuel efficiency;  and is capable of detecting minor issues or glitches before they actually occur, among so many other beneficial features.

However, like every coin has two sides, and as there are always two side to every story, there is also a reaction to every action.   Meaning for every beneficial feature of OBD-II there is a detrimental feature to OBD-II. OBD-II is essentially a computer system with a host of additional computer modules remotely placed through the body of the car, some of which have an effect on the Engine ECU. 

These modules or sub-ECUs oversee various features, like an airbag controller module/ECU that supervises the airbag. This module is connected to crash sensors placed in strategic positions in the car, that triggers when a crash occurs and ensure that the airbag is inflated within the required time frame. Then there is also an immobilizer module/ECU that supervises the starting process ensuring the correct code from the key transponder chip corresponds with its randomly generated code. There is also an ABS Brakes module, a Gateway module, a Steering Assist module, an Instrument Module, a Central Convenience module, a Radio module, to mention but a few. All of which are potentially sources of problems.

If we only look at the Airbag and the Immobilizer modules/ECUs, both will impede driveability and the starting of the car, by influencing the Engine ECU. If the Engine ECU doesn't received the expected signal from either, it would refuse to start the engine. The Engine ECU is the heart of the ODD-II and normally sits in the engine compartment or inside the car under the dashboard. All three these modules/ECUs mentioned, sometimes also referred to as nodes, are in within a meter of on another but here's the downside. 

To get them to sing in harmony they are connected together by a wiring harness. This wiring harness plugs into each and every node in the car, and also share a common twisted-pair wire-connection  called a bus which is terminate at each of its ends with 120 Ω resistors. This bus can be either Controller Area Network (CAN) or  Local Interconnect Network (LIN) or even FlexRay. Each module also has a power supply and an earth connection. All of these wire connections are potentially sources of problems.

The average car can have anything between 5 and 100 modules/ECUs, some ECUs have as few as six connections and others as many as 80 or 94 or even more. Each of these physical connections are prone to corrosion, metal fatigue and physical flexing due to suspension vibration and is a source of future problems. Some ECU's earth connection is solely made through body contact and if it looses contact due to vibration or water ingress, it will undoubtedly cause an error or errors. 

These errors are stored in the ECU's non-volatile memory which can at times be quite cryptic. I can say that without doubt that every "automotive technician" has misinterpreted DTCs and replaced unnecessary components in the process. Even returned cars to the owners claiming that they solved the problem but didn't, they were just under the misapprehension that they did.

If any connection out of this glut of connections becomes intermittent for some reason or the other, it would be like trying to find a needle in a haystack and there are so many "automotive technician" that have never touched a needle nor even seen a haystack, let alone find a needle in a haystack. Be that as it may, one of the advantages of OBD-II is that it increases the likelihood of a DIY fix, providing the fixer is fairly dexterous and have some electronic and mechanical knowledge and have access to a diagnostic scanner.

A fairly common plug connection that goes intermittent, is the one that connects to the throttle body. It supplies the voltage to the stepper motor that controls the throttle butterfly valve. This plug also sends feedback to the ECU so that it knows how wide open or close the valve is. So many mechanics insist on stripping the throttle body due to a throttle body DTC and claim after cleaning it, the problem was solved. However a few days later the error would be back. A word of caution, Don't suspect replaceable parts especially if it has less that 100 000 km on its clock. Exhaust the possibility that it's a possible wiring harness problem before replacing expensive items because they can never be returned to the agents after its been installed.

Another intermittent connection it the 6 pin plug that interfaces with the accelerator pedal. This is a common source of the dreaded EPC problem. In many cases, a squirt of electro cleaner may solve this problem. That's to say until it's triggered by something else. It's worth while to check the voltage supply stability and ground impedance between the 6 pin plug and the ECU. Remembering that the pedal's earth connection is grounded inside the ECU and the ECU is grounded to the body or chassis and not the engine. In some cases, the ECU will function normally because its metal casing is not earthed.

Also, don't be tempted to earth the pedal earth directly to the body when there is a  significant resistance reading. Rather replace that portion of the wiring harness that may have gone high resistive. Offset ground connections and ground loops can cause voltage drops and magnetic impedance which are major causes of noise hum, and interference in computer systems (ECU). So don't alter the the existing ground connections because it could introduce issues you've never experienced before.