VW AND AUDI EPC SOLENOID

VW AND AUDI EPC SOLENOID REPLACEMENT 

Its been four months since the accident that triggered both my VW Polo's airbags. Even though damage to the body was slight, my polo has been standing for all this time while repairs were effected. Now that everything is fixed and ready to take the Polo on the road once again, there appeared to be a huge problem. I couldn't select any gears whilst the engine idles because it grinds horribly but was able to select them when the engine is off. I have even selected a gear then turned the ignition, just to see it the clutch and pressure plate engages. After several attempts at grinding every gear, I came to the conclusion it may not be the gearbox that's at fault but perhaps the clutch that is not disengaging from the flywheel sufficiently.  So I started the engine and pumped the clutch for a several minutes. Thereafter it started selecting gears with difficulty and after several attempts it was back to normal. I took the Polo on the road and every thing was just great. 

02E  Automatic Transmission EPC Solenoid DSG  Gearbox  valve body   (Electronic Pressure Control) solenoid 

This so reminds of my friend Aron who also had or rather is still having a nasty transmission problems with his Jetta.  When he selects a gear, there is  loud thud coming from the transmission, then the  P, N, R, 1, 2, 3 light in the  instrument cluster flash red for a while then just stays on. In fact the light display is reversed, solid red back ground with whiteout text.  His car is fitted with DSG transmission. Direct-Shift Gearbox (DSG), Multitronic DSG / CVT Transmission  repairs can be and are invariably quite expensive and this problem looked and sounded very expensive. So to save money, he decided to repair it himself.  After watching what he had to do, I realized that a bad transmission is definitely not a DIY project, unless you have the mechanical and electronic expertise and the necessary specialized equipment. 

A 02E transmission scan came up with the following data:- 

 Address 02: Auto Trans Labels: 09G-927-750.LBL
Control Module Part Number: 09G 927 750 HJ HW: 09G 927 750 CJ
Component and/or Version: AQ 250 6F 1068
Software Coding: 0000072
Work Shop Code: WSC 31414 000 00000
4 Faults Found:

17104 - Transmission Output Speed Sensor (G195): Circuit Malfunction
P0720 - 012 - Electrical Fault in Circuit - MIL ON
Freeze Frame:
Fault Status: 10101100
Fault Priority: 2
Fault Frequency: 1
Reset counter: 44
Mileage: 104552 km
Time Indication: 0
Date: 2010.10.19
Time: 16:39:08

17099 - Transmission Input Speed Sensor (G182): Circuit Malfunction
P0715 - 012 - Electrical Fault in Circuit - MIL ON
Freeze Frame:
Fault Status: 10101100
Fault Priority: 2
Fault Frequency: 1
Reset counter: 39
Mileage: 41353 km
Time Indication: 0
Date: 2015.08.08
Time: 00:00:00

17094 - Transmission Fluid Temp.Sensor (G93), Circuit Malfunction
P0710 - 010 - Open or Short to Plus - Intermittent
Freeze Frame:
Fault Status: 00101010
Fault Priority: 2
Fault Frequency: 1
Reset counter: 184
Mileage: 41353 km
Time Indication: 0
Date: 2015.08.08
Time: 00:00:00

01680 - ABS Wheel Speed Signal; Front Right
013 - Check DTC Memory
Freeze Frame:
 Fault Status: 00101101
Fault Priority: 2
 Fault Frequency: 7
Reset counter: 201
Mileage: 41353 km
Time Indication: 0
Date: 2015.08.08
Time: 00:00:00

The transmission gets  a speed signal from the front right side wheel which is needed by the TCM to determine the speed of the car and when it should change gears hence there is an ABS fault listed above. After stripping the valve body, he found that the transmission oil looked like there was water in it, a sort of milky grey instead of reddish translucent. It turned out that the previous owner never bothered to replace the transmission oil at all. There were iron fillings attached to the magnets in the sump and some black plastic bits from the solenoid plugs could be seen in the oil, liquidized by the gears.  This most likely caused solenoid EPC (electronic pressure control) solenoid to seize, preventing it from moving when pulsed because it caked-up around the plunger.  In fact the entire loom was so brittle when  it was unplugged that it just disintegrated into crumbs.  Considering that the engine is attached to the transmission, both of which produce tremendous heat which virtually "cooks" the transmission oil at 40 degrees C. Its no wonder the transmission harness  is overcooked hard and brittle because it lies in this hot oil. It's also very surprising that VAG cars with DSG transmissions aren't more trouble some than they already are, because the electronic mechatronic unit sits inside the gearbox. As bad luck would have it, Aron's Jetta's mechatronic device was fried and needed to be replaced along with the internal harness.  No electronic component other than "military spec electronic components" was designed to withstand of survive such huge amount of heat.  

Anyway, the EPC (Electronic Pressure Control) solenoid was replaced after the valve body tunnels was cleaned with a rifle cleaning wire brush and reassembled. Two more rubber seals on two other solenoids were also replaced and as mentioned earlier, the mechatronic unit and the internal harness.

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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EPC light came on and can't start the engine,  / EPC warning symbol came on today while driving, / VW Polo EPC  Warning Light came on and lost power.  / Can I drive with EPC light on? / VW Polo no Throttle and EPC light on, / What causes the EPC light to come on? / What does EPC mean on the dashboard? / What is an EPC light?  / What is limp mode,  / What is limp-mode home?, / What is the VW EPC Warning Light, / What is EPC on a Volkswagen? / What does the EPC light mean on a VW, / What does the EPC Warning Light on my dashboard mean, / What does it mean if the EPC warning light comes on in a Volkswagen, / How to Fix EPC Light on a VW,  / What is an EPC light on Volkswagen?, / What Is the VW EPC Warning Light? / What does it mean if the EPC warning light comes on in a Volkswagen?  / What does an EPC light on the dash of a Polo car mean?

Loss of Power

LOSS OF POWER

On Sunday past, whilst taking my family for a drive along our scenic coastline on the Western Cape, I happened to see no less than three Volkswagen cars, each being loaded onto a roll-back. A VW Polo Vivo in Muizenberg, an Audi S4 in  Fish Hoek and a VW Scirocco in Scarborough. I couldn't help but feel awkward about my own Volkswagen Polo because after all, three out of three vehicles on the roll-backs were Volkswagen manufactured cars. I would have felt loads better if at least one of them were a Toyota or a Ford or a Honda. Understandable there are a lot more Volkswagen vehicles on the road than any other make, hence the higher failure rate.  

However, I instinctively pulled over for a chat with the driver of the Scirocco to inquire about the problem. It's owner Gwendaline. apparently parked her car to go for a walk on the beach and when she returned, had difficulty in starting her car. When it finally started , the whole car shook like her washing machine does in its spins cycle.  According to her, the Scirocco  is  really an excellent car with very few issues other than regular EPC light issues; and that its 18 inches tyres are a bit expensive. So we started talking about the EPC - Electronic Power Control and she seems really knowlegeable about it.  Our conversation went something like this.

Electronic Power Control

The EPC warning light, is just an indicator light powered by the Electronic Power Control circuit. Most people are under the impression that it indicates that there is something wrong with the engine when it light up. But this is not exactly the case, because the EPC light does come on when a brake light is fused or the fuel tank cap isn't properly closed.  When The EPC warning light flashes or stays on, it merely alerts the driver to a problem that may exists in your Volkswagen's throttle system. The throttle system encompasses  the throttle body, the throttle control motor, the accelerator pedal, the drive-by-wire electronics, the traction control, the cruise control, the stability control, the fuel delivery system and even the braking system and all their sensors, etc.. 

What does it mean when the EPC warning light turns on in a Volkswagen?

The throttle body motor opens and closes the butterfly valve located on the intake manifold which regulates the amount of air that goes into the engine, in relation to the position of the accelerator pedal. Implying the higher the air flow into the engine, the more fuel the ECU injects, thereby increasing  or decreasing the power output of the engine. When a problem is detected in the throttle system, a signal from one of the sensors triggers the  ECU into illuminating  the EPC  warning light. 


The Electronic Power Control (EPC) is just a part of the Engine Management System, which in turn is part of the overall On-Board Diagnostic II system. Normally when the a problem is detected that causes the EPC light to turns on, it also sends fault codes to the dashboard module or gateway module, vehicle model dependent. These fault codes can be retrieved by an ODBII scanner / smart phone, which are key to isolating the area of the throttle system that has failed. Most EPC light and ESP light problems will limit your Volkswagen's output power, commonly known as "limp mode".  

It is advisable that when either the EPC or ESP lights turn on, the problem associated with it be repaired timeously. A Volkswagen in limp mode should not be used to run errands, and since the car has sufficient power to drive it to  dealership or mechanical repair shop, it is best to do so. Normally once the fault / problem is remedied the EPC or ESP light will turn off. However, there are hundreds if not thousands of Volkswagen owners who have taken their Volkswagen cars into dealerships for repair, only to encounter the same EPC / ESP problem a day or two later.  Some of them suffer with EPC problems for months and I personally know of someone who had an EPC problem for more than a year. That's enough to drive the sanest person nuts.

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My W Polo classic 2003 model's EPC light is on and there's no acceleration. My VW Jetta's dashboard displays the word  EPC, now it has no power. My VW Golf diplay the letters Epc, what can I do?  My VW Golf IV cluster shows both epc and esp and it won't revv up, nor go more than 70 km/h. My VW Sirocco 2017 model's epc light has come on again. My car's EPC light is on and I don't know what to do?  

EPC LIGHT

EPC LIGHT

A few months ago the battery in my VW Polo Classic remote key, gave up the ghost.  I used the remote key to lock the car and set the alarm / immobilizer the night before but it refused to open the doors the following morning. So I unlocked the car with the key.  That’s when I realized that my 2007 VW Polo Classic Highline only has one door lock and that I only had access via the driver’s side door.   Neither the left side passenger door nor the rear doors on either side have any locks keyholes. This didn't surprise me because cutting cost has become the new standard in new car design. By not fitting these legacy locks, the car manufacturer saves the cost of three locks, the internal door mechanisms and the labour cost to install them when the car is assembled.  Multiply this amount of savings by the entire vehicle production for the year and you can surely see their total saving.

The Battery inside the electronic key housing.

That brings me to another cost saver implemented in most cars manufactured during 1996 and later. If you heard about OBD II (On-Board Diagnostics II) and CAN-Bus (Controller Area Network-Bus), you will have some notion what I am talking about. With the implementation of CAN-Bus auto electric wiring has been reduced to a bare minimum.  The average older car had between 300 – 400 meters of wiring, used for its head lights, tail lights, windscreen wipers, horn, dashboard electrics, alarm system, central locking, interior lighting etc, etc ...  Much of this wiring are roughly the same thickness (0.5 - 1.5 mm square) to carry the required current to the various devices.  But inside the engine compartment there are numerous thicker wires for the starter, ignition, air conditioner fan motor, alternator, main supply to the fuse box as well as  earth straps to mention but a few.   All these copper wires range between 1.5mm square – 15mm square, some of which are tin plated to minimize corrosion. Not only is this 400 meters of copper wiring expensive, it also weights a good 60-70 kgs.

By embracing the CAN-Bus technology, manufacturers save on the purchase of about 50Kgs of copper wire. Fifty kilograms of copper wire multiplied by the annual car production gives you some idea of the overall saving. Fifty kilograms taken off the weight of a car also gives it a better 'power to weight ratio' hence making it more fuel efficient.  With CAN-Bus technology,  all the  control modules in the car are interconnected, on a serial data network, each module taking charge of a sub circuit of  the electrical system. These modules are network similar to USB (Universal Serial Bus) used in computer networking.

VW EPC LIGHT

However,  CAN-Bus and OBD II was not implemented to save copper, nor to lessen the weight of cars neither to make cars  more fuel efficient.  It was firstly agreed upon by the EPA, then legislated by several Governments whose countries manufacture cars, to install an EMS (Engine Management System) in every new car built after 1996. This management system would monitor the engine and transmission of the car and insure that 'engine emission levels' stayed within a predetermined margin of compliance.  If this level is exceeded due to engine malfunction, the embedded diagnostic system should be able to recognize it and recorded such malfunction and also alert the driver with some form of MIL (Malfunction Indicator Light). Alternatively turn on the EPC light (Electronic Power Control - epc warning light) and stops the  car from revving up or  inhibit the management system and shut the car down.  The frequency of engine misfires or malfunctions are recorded in code format (vw epc code) designed by the Society of Automotive Engineers (SAE) in the ECU's non-volatile memory which is only accessible by the service agents or by someone with a modern day ODB II / CAN-Bus compliant diagnostic scan appliance.

Anyway let me return to the story of the remote control battery. Off I went to the local VW agent to buy a replacement battery.  I drove  a good 40 Km there  and back but still returned without the battery. It was just way too expensive for a small mercury cell. Problem was, I didn't phone to find out how much it cost. At the price that this VW agent charged for the  fob key battery I could manufacture it myself and it would still be cheaper. So I scouted around at a few photographic shops for this particular battery and eventually found a pharmacy that sold them. Hypothetically, if I bought all the pharmacy’s battery stock and sold it to this VW agents at half their asking price I would in fact have made a very comfortable living.

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HOW TO FIX AN EPC PROBLEM - CONTINUED

HOW TO FIX AN EPC PROBLEM, - CONTINUED

The final note on the preceding blog installment ended on 'scan for Diagnostic Trouble  Codes with a scan tool'. However before we start scanning it is important to note, that Vehicles from year 2000 are fitted with an EPC (Electronic Power Control) system, hence this exposée only applies to cars fitted with a obdii 16 pin female connector, identifiable by its  normally purple core, roughly the same purple of the 6-pin mini-DIN connector  of a personal computer keyboard.  This EPC system / Drive-by-Wire circuit (implying no throttle cable) is also known as the torque circuit. The EPC system controls the EPC light  which turns on if and when there is the slightest malfunction  in the Drive-by-Wire circuit. Any such fault will more than likely generate a DTC (fault code) in the ECM, which is stored in its non-volatile memory, meaning even if the battery is disconnected afterwards the DTC (fault codes) will persist. However, also note that when the battery is disconnected all driver learnt values particular to your driving style, will be erased. Disconnecting the battery may require resetting the convenience electronics, such as alarm, interior lights and the radio. So, most importantly if you don't have the radio code, practice caution because the radio will permanently lock-up hence it's a good idea to use a jumper battery or perhaps even a battery charger to maintain battery power whilst replacing a battery. Or get the code from your service center.

Whilst any problem in the torque circuit is  normally responsible for turning on the EPC light,  the EPC light may also turn on for some other non-emission related engine faults.  When a combination of emission-related and EPC-related fault is encountered, both the MIL and EPC lights may turn on. This alone give one a good idea of whether or not the engine problem is purely torque related or part of an emission-relate issue.

Most pure torque circuit EPC faults are accompanied by Limp-Home Mode which revolve around the basic settings for the Electronic Throttle Control Valve Adjuster, Idling Control, EPC Adaptation and the  Accelerator Pedal Position Senders. Their values are stored in the ECU normally from group 60 - group 62 of the Bosch ME 7 and newer ECUs, however the actual group may vary subject to make, model and engine capacity of the vehicle. For example. Jetta, Polo, Audi TT, etc, EPC adaptation exists at group 060 - group 062, whereas these values may be stored in group 098 for some VW Passat and Audi A4, S4, B5.

Group=060, Adaptation Epc-system
Group=061, Epc-system (1)
Group=062, Epc-system (2)

Emergency Running or Limp-Home Mode

Both Bosch Motronic and Siemens Simos ECU have two emergency running modes to compensate for accelerator pedal sender failure. The first mode triggers when the primary sender G79 (Sender -1) accelerator pedal sender fails, and the second mode triggers when both G79 and G185 (Sender -2- redundant sender) accelerator pedal senders fail. In the first case with one accelerator pedal sender failing, the accelerator position is limited to a predefined value (limp mode) idling speed while some comfort functions will be disabled,  the Air Conditioner for example. By which time EPC light would have already illuminated. However, when the second emergency mode triggers the engine runs only at idle speed. It would be exactly like disconnecting / removing the accelerator pedal completely. On the occasion that I replaced my accelerator pedal, I started the engine and to my surprise it started perfectly normal and idled at a normal rev. So the conclusion is when both accelerator pedal senders / potentiometer fail, it gives you the same, exact, identical symptoms of a physical steel accelerator cable that snapped. Considering a throttle cable is the single most important part of the throttle system in a car engine. So when it breaks the car will idle, but will not rev. The EPC system mimics the pysical cable exactly or as near as dammit.

Siemens Simos ECU J361 with pin connections

Looking at the diagram for accelerator pedal senders G79 and G185, pins 50 and 19 are inputs from their respective highside driver 5V supplies with pins 18 and 45 of the ECU microprocessor are their independent internal earth connections. The two variable voltages at pins 51 and 64 are the inverse of on another. Essentially G185 (secondary) is working as a backup to G79 (primary). Inputs at pins 51 and 64 are constantly monitored by the ECU microprocessor could range from sporadic to too high or too low, to intermittent to absolutely not there. The  ECU microprocessor with its built-in Watchdog Supervision Safety Logic monitoring performing plausability checks for voltage regulation, Over/Under voltage levels, intermittent voltage levels. If for any reason that the calculations based on its internal algorithms do not correspond to its internally stored and expected values either the watchdog processor or the  Main Processing Element enable   a secondary shutdown path to all equipment under its control. In a nutshell, limp mode.

Constant movement of the gold plated contacts on the potentiometer slider eventually wears through and becomes intermittent especially if the vehicle has attained a high millage, considering  how may times the accelerator pedal has been stepped-on and released. It can be roughly compared to a volume control that's gone scratchy from constant use, when it finally worked through its carbon track and makes intermittent contact.  I've known physical  steel throttle cable to last a lot longer than its electronic counter part but they do have a tendency to fray and get stuck inside its sleeve especially when going at high speed, which is kinda dangerous -even life threatening.  With the EPC system this will not happen, rather if the "electronic steel threads fray" the microprocessor shuts the system down by switching over to its stored alternative values.

Looking at the diagram for G188 and G187 it can clearly be seen that they share a common 5v supply (pin 91) and a common earth (pin97) with the outputs from pins 90 and 92 acting as inputs to the ECU microprocessor that control for the throttle valve actuator motor. These inputs are also constantly monitored by the ECU main Processor and its companion watchdog processor. Noting once again that G188 and G187 act as angle sensors much like that of the accelerator position senders. The concept and principal is exactly the same as that for the accelerator potentiometers. When any discrepancy is detected, a shutdown path is enabled which presents itself to the motorist as a car that won't rev. Then there is G61, the knock sensor. Any  knock higher or vibration outside of that expected by the ECU on pin 102 will also enable a shutdown path and sequence limp mode. 

Accelerator 6 pin plug and harness for VW, Golf, Skoda, Fabia, Audi etc.

Accelerator Pedal 6 Pin Plug Connector Wiring Harness for VW, Amarok, Beetle, Eos,
Lupo, Polo,Touareg, Sharan, Transporter, Electronic  - 3B0 972 706

Based on this, the inputs and outputs from these three components are vital to the correct functioning of any Drive-by-Wire vehicle. So when a fault occurs and guided by error codes, it is important to ensure that there is wired continuity between these components and the ECU connector. Wiring harnesses are subjected to a fair amount of shaking and can break inside of the PVC sleeving. Especially sensitive is the 6 pin Electronic Accelerator Pedal Plug Connector Wiring Harness for VW Polo, Golf, Audi, Skoda, Fabia. VW part number - 3B0 972 706. This replacement part needs to be soldered onto the  wiring harness after cutting off the original plug.

The Most Common Car Problems

There was a time when car owners could easily service their own cars. Simply replacing points, plugs and condensors,  draining its oil and replacing its oil and oil filter normally put the car back on the road again. Those were the days when the most common roadside problem was a puncture or a snapped fan belt. Punctures were easily fixed with a replacement tyre from the trunk. All that was needed was some elbow grease applied to the jack, wheel brace and wheel nuts and you were on the road again. But today rollbacks are are integral part of motoring. Hundreds of cars are loaded up everyday on the road side.

The main cause of punctures was attributed to poor road surfaces, random metal objects and broken glass and to a lesser degree older tyre technology. Even though punctures were predominant, they were by no means exclusive to roadside breakdown because clutch plates and gearbox problems were also plentiful, as was running out of fuel.

With the advent of newer cars, the race for the most fuel efficient and least expensive car was on. When fuel and air stoichiometrics were at its peak, car manufactures started producing cars with a 'Space Saver Biscuit Spare Wheel' which took several kilograms of weight out of the trunk, This made the car a tad lighter, slightly more fuel efficient and ever so slightly, cheaper to produce.

Today, almost a third of all new cars don't even have a spare wheel; instead they may be equipped with a can of self inflating puncture-repairing foam, or an electrical air compressor with some sealant kit to temporarily fix a flat tyre. Both options are evidently cheaper than a Space Saver Biscuit Spare Wheel and lighter.

However, believe-it-or-not, the more expensive cars today, are sold without  a spare wheel, instead they are fitted with “run-flats”. In a nut-shell, run flats are special pneumatic tyres, designed to resist the effects of deflation when punctured, yet enables the car to  be driven at reduced speeds of under 90 km/h for a distance of up to 80 km. The speed and distance of course to the nearest tyre repair shop, is subject to the type and quality of the “run-flats”.  So, once again the manufacturer saves the cost of supplying a spare wheel.

Be that as it may, snapped fan belts  often causing the engine to overheat, sometimes resulted in a  blown  cylinder head gasket. Subsequently, the modern day electric radiator fan has totally supperceeded the belt driven fan and as a result, burst radiator hoses, corroded, leaking water pumps and welch plugs have  became the primary cause  of blown cylinder head gaskets. The other bugbear is oil leaks that weren't timeously attended to, currently trending as the most common cause of seized engines. 

With the abundance of electronics fitted into cars, the alternator  and its voltage regulator have  became a lot more more troublesome than ever before. Obviously due to the additional electrical load.  Alternator  problems are closely followed by starter issues when either its brushes or its  bendix reaches its end of life.   

Both types of problems have resulted in batteries being replaced prematurely and sometimes unnecessarily. Brakes and Turbos also give their fair share of problems, but none of these problems comes close to the new type of roadside breakdowns caused by the OBD-II system.

The most common cause of  breakdowns today, is the Electronic Power Control (EPC) light; not that the light is the cause of the problem. The Electronic Power Control (EPC) light is only an advisory light, drawing your attention to a possible malfunction or  pending problem or  already existing problems.

When the Electronic Power Control (EPC) light comes on, without the ESP or Check  engine light, the car is normally still driveable, even if it goes into limp mode. But when accompanied by the ESP and or CEL (check engine light) the car may refuse to start as its inhibited by the Electronic Computer Unit (ECU). 

When this happens, the only solution is to secure a rollback to fetch the car and take it either to your service agent / mechanic or your home, so that you can tend to the problem yourself. 

There is no way you'd be able to effect repairs to your car yourself without a OBD II scanner   that would direct you to, or confine your repair to a certain area of the engine. 

Below are a few sample yet partial ODB II diagnostic scans  for Electronic Power Control (EPC) problems. 

This for a 7N0 - VW Passat.
Address 01: Engine (CDL)       Labels: 06F-907-115-CDL.clb
   Part No SW: 1P0 907 115 AB    HW: 8P0 907 115 B
   Component: 2.0l R4/4V TFSI     0020  
   Revision: 5BH20---    Serial number: 0000              
   Coding: 0303004C18070160

1 Fault Found:
008487 - Accelerator Position Sensor 2 (G185) 

               P2127 - 002 - Signal too Low

Electronic Power Control (EPC) problem  for a 1J - VW Golf.

Address 01: Engine Labels: 06A-906-032-AWP.lbl

Part No: 06A 906 032 RN

Component: 1.8L R4/5VT G 0001 

Coding: 07510

18047 - Accelerator Position Sensor 1/2 (G79/G185) 
            P1639 - 35-00 - Implausible Signal
18042 - Accelerator Position Sensor 2 (G185) 

            P1634 - 35-10 - Signal too High - Intermittent

Electronic Power Control (EPC) problem  for a 7L - VW Touareg 

Address 02: Auto Trans        Labels: 09D-927-750.lbl
   Part No: 09D 927 750 AN
   Component: AL 750 6A           0546  
   Coding: 0004153


1 Fault Found:
00777 - Accelerator Position Sensor (G79) 

            004 - No Signal/Communication - MIL ON

NB! The Automatic Transmission module and not the Engine Module detected this accelerator sensor problem.

 

Electronic Power Control (EPC) problem 1H - VW Golf/Vento III
Address 02: Auto Trans       Labels: 01M-927-733.LBL
   Controller: 01M 927 733 CT
   Component: AG4 Getriebe 01M    3363
   Coding: 00000
    

1 Fault Found:
00518 - Throttle Position Sensor (G69)

            16-10 - Signal Outside Specifications - Intermittent

NB! The Automatic Transmission module and not the Engine Module detected this accelerator sensor problem. Here the Throttle position sensor instead of the Accelerator sender is the cause of the problem.

Electronic Power Control (EPC) problem  for a 9M - VW Jetta IV.
Address 01: Engine Labels: 06A-906-032-AWP.lbl
Part No: 06A 906 032 RN
Component: 1.8L R4/5VT G 0001 
Coding: 07510

1 Fault Found:
18047 - Accelerator Position Sensor 1/2 (G79/G185) 

P1639 - 35-00 - Implausible Signal 

Electronic Power Control (EPC) problem  for a 8E - Audi A4.
Address 01: Engine Labels: 06C-909-559-ASN.lbl
Part No SW: 8E0 909 559 D HW: 8E0 909 059 
Component: JHM V3/9X G 0003 
Coding: 0016751

2 Faults Found:
18047 - Accelerator Position Sensor 1/2 (G79/G185) 
P1639 - 008 - Implausible Signal - Intermittent
18047 - Accelerator Position Sensor 1/2 (G79/G185) 

P1639 - 008 - Implausible Signal - Intermittent - MIL ON

Electronic Power Control (EPC)  for a 8P - Audi A3.
Address 01: Engine Labels: 06A-906-033-BGU.lbl
Part No: 06A 906 033 DS
Component: SIMOS71 1.6l 2V 5559 
Revision: --H03--- Serial number: AUX00000
Coding: 0000071

4 Faults Found:
18047 - Accelerator Position Sensor 1/2 (G79/G185)

P1639 - 008 - Implausible Signal - Intermittent

Electronic Power Control (EPC) problem  for a 9M - VW Jetta IV

Address 01: Engine Labels: 06A-906-032-AWP.lbl

Part No: 06A 906 032 LP

Component: 1.8L R4/5VT G 0005 

Coding: 07500

18042 - Accelerator Position Sensor 2 (G185) 
P1634 - 35-00 - Signal too High
18039 - Accelerator Position Sensor (G79) 

P1631 - 35-00 - Signal too High

 Electronic Power Control (EPC) problem  for a 1C - VW New Beetle

Address 02: Auto Trans Labels: 01M-927-733.lbl
Part No: 01M 927 733 EN
Component: AG4 Getriebe 01M 4108
Coding: 00000

1 Fault Found:
00518 - Throttle Position Sensor (G69)

16-10 - Signal Outside Specifications - Intermittent

NB! Once again the Automatic Transmission module  detected this Throttle position sensor instead of the Engine Module detecting the Accelerator sender to be the cause of the problem.

___________________________________

As can be seen from the data above,  there are essentially 3 types of  DTC errors responsible for triggering the EPC light, though not exclusively. P codes  P1630 and P2122;  P1631 and P2123;  P1632 and P1861 are essentially the same and applies to sender 1. 

As can be seen below.
P1633 and  P2127;  P1634 and P2128; P1639 and P2138 are essentially the same but applies to sender 2. There are also several other DTC errors that can and trigger the EPC and or along with the ESP, and or with the CEL.

Accelerator Pedal Sensor 1

P1630 - Accelerator Pedal Pos. Sensor 1 (G79), Signal too Low

P1631 - Accelerator Pedal Pos. Sensor 1 (G79), Signal too High

P1632 - Accelerator Pedal Pos. Sensor 1 (G79), Power Supply Malfunction

P2122 - Accelerator Pos. Sensor 1 (G79), Signal too Low

P2123 - Accelerator Pos. Sensor 1 (G79), Signal too High

P1861 - Accelerator Pos. Sensor 1 (G79), Error Message from ECM

Accelerator Pedal Sensor  2

P1633 - Accelerator Pedal Pos. Sensor 2 (G185), Signal too Low

P1634 - Accelerator Pedal Pos. Sensor 2 (G185), Signal too High

P1639 - Accelerator Pedal Pos. Sensor 1/2 (G79) / (G185), Implausible Signal

P2127 - Accelerator Pos. Sensor 2 (G185), Signal too Low

P2128 - Accelerator Pos. Sensor 2 (G185), Signal too High

P2138 - Accelerator Pos. Sensor 1/2 (G79) + (G185), Implausible Signal

Throttle Position Sensor

16505/P0121/000289 - TPS (G69): Implausible Signal
16506/P0122/000290 - TPS (G69): Signal too Low
16507/P0123/000291 - TPS (G69): Signal too High

Throttle Angle Sender 1

17950/P1542/005442 = Angle Sensor 1 for Throttle Actuator (G187): Implausible Signal
17951/P1543/005443 = Angle Sensor 1 for Throttle Actuator (G187): Signal too Small
17952/P1544/005444 = Angle Sensor 1 for Throttle Actuator (G187): Signal too High  

Throttle Angle Sender 2

16605/P0221/000545 - Angle Sensor 2 for Throttle (G188): Signal   Implausible 
16606/P0222/000546 - Angle Sensor 2 for Throttle (G188): Signal Too Low
16607/P0223/000547 - Angle Sensor 2 for Throttle (G188): Signal Too High

Depending on the model of your vehicle, its Throttle position sensor (TPS) lowest output voltage should be around .17 Volt and when the Electronic Control Unit (ECU) detects that it has dropped below that, then it will trigger either a P0122 or P0222 code.  High signals are not common but they do occur. 

 

As can be seen from the above data the error signal is either too low or to high or intermittent/implausable. Bearing in mind that a constant 5 volts is supplied by the ECU via a High-side or Low-side driver to the each of these potentiometers (senders). Loss of the voltage or even intermittently loss will trigger the EPC light and enter into "limp mode".

By implication  the monitored output is in 1 of 3 states, viz, low, high, or intermittent. In order to determine these states, the ECU needs a reference to compare these signals against. Each sender therefore act as a reference for another and any discrepancy between the two can result in an EPC error and subsequent limp mode. 

Replacing the Accelerator Pedal sensor (potentiometer)  unit normally fixes the EPC problem, but limp mode can also be caused by the throttle butterfly potentiometer.  And like I mentioned before, an OBD-II diagnostic tester would make this repair a lot easier and a lot faster.


NB! When your car goes into "limp mode", you may have  a lit   "Engine Management Light" (EPC icon) and or a "Electronic Stability Light" (skidding car icon) and or a "Engine Control Lamp" (engine icon) or any other combination thereof.  

Even Earthworks machinery are fitted with OBD-II so that exhaust emissions can be controlled but when there is a problem in the OBD-II system, invariable these machines would have to go on a roll back and taken for repair.

 

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