Check Engine Light

Check Engine Light - aka MIL

Yesterday morning when I started my VW Polo highline she idled a bit rough but I never gave it another thought because it had been raining hard throughout the night with harsh howling winds accompanied by a  lightning storm. I summized it could have been caused by the moisture in the air but when I looked at the dashboard, I saw that the orange / amber Check Engine Light was on. I tried accelerating and looked at the CEL but it stayed on. Surprisingly the engine seemed sluggish and didn't revv as per normal. Looking through the rear view mirror, I could see a distinct amount of smoke spiraling behind the car.  This was worrying because the previous day,  the car drove perfectly normal and when I parked her, she idled just fine. 

The problem with the  Check Engine light, other that being on, is that it doesn't tell you anything about the nature of the problem nor whether it's  serious or not. All I knew is that something was wrong with my emission control system because of the excessive  smoke.   The Check Engine light is actually better known as the Malfunction Indicator Lamp (MIL) so in essence there was a malfunction detected by the ECU and there was no way to tell what it could be without plugging in my scan tool. So off I went and  fetched my laptop and my VCDS cable, plugged it into the under dash DLC connector and ran a scan and found 4 Faults - P1137, P1103, P1187, and a P0441.

CODE ERRORS

17545 - Fuel Trim: Bank 1 (Add)
P1137 - 002 - System too Rich - MIL ON

Considering the first error code describes the fuel system as to rich, by implication then there is too little air for proper combustion. So I popped the bonnet to check the MAF, and saw a whole load of leaves and pine nettles strewn all over the engine compartment and a hand full of them stuck to the inlet of the air filter, blocking the air flow. I then open the air filter, removed the leaves and nettles and all those that got sucked into the air filter housing when I initially started the car.

17595 - Linear O2 Sensor; Compensation Resistor: Open Circuit
P1187 -- 35-10 - - - Intermittent

The second error directed me to the O2 sensor because the ECU describes it as  "Open Circuit".  Stooping over the engine, my eye followed the exhaust pipe, from the manifold branch past the firewall and saw a pine tree branch under the car, so I kneeled down to pulled it out but is was stuck. The tree branch was right below the  Catalytic converter.  I then went inside to fetch a garden pruning scissors so that I could cut off the protruding twigs and free the branch. Just as I was cutting I saw a wire hanging from down from the Cat. It was the wire from the O2 sensor that broke off and I supposed this happened with the force of the wind blowing the branch under my Polo.

The road and my driveway was littered with pine comes and nettles that the wind blew from the park more than a 100 meters away.  Anyway, I striped of the O2 sensor wires which was screened and reconnected them with an electrical block connector. You know the ones were you have to push the wires into a brass ferrule from either end and screw it down with the two screws. That just worked perfectly.

17511 - Oxygen (Lambda) Sensor Heating; B1 S1: Performance too Low
P1103 - 35-10 - - - Intermittent

The third error also directed me to the O2 sensor that wasn't heating up. I suppose it's linked to the disconnected wire and I assume the ECU prevented this because it realized the O2 sensor was OC. 

16825 - EVAP Emission Control Sys: Incorrect Flow
P0441 - 35-10 - - - Intermittent

The fourth error I couldn't make sense of  though I've seen this error when the fuel tank cap wasn't properly closed. So I went to the the tank, took off the cap and inspected the rubber seal. But it all seemed fine, so I closed it. I them cleared the diagnostic trouble codes (DTC) stored in the engine control module and started and re-scanned the ECU for errors and it came back with "No fault code found ". I then started my Polo and all was well. She revved as before and the Check Engine light was off.


The Check Engine light has always been a major annoyance to both motorists and mechanics,  and as a consequence is often ignored. I even know of someone  who stuck a piece of black insulation tape over the orange / amber  Check Engine light to blot it out, rather than fix the problem. Be that as it may,  ignoring the Check Engine light could lead to expensive car trouble later, so it's important to promptly address problems indicated by it.

DIY mechanics should buy and inexpensive scan tool / DTC code reader  since they are all standardized to plug into the 16 pin DLC under the dashboard. It would empower them to  discuss the problem with their mechanic if they can't manage to solve it themselves. When Check Engine light comes on, it is more likely than not that your car car is releasing unburnt gasoline (hydrocarbons) and carbon monoxide  into the atmosphere and consume a lot more fuel than it actually should.  

The OBDII system was primarily designed to monitor the emission control system continuously so it can be said hat if you car passes "readiness" its a good indication that your car  engine is in good health.  

Some problems that can illuminate the Check engine Light.

A clogged air filter can trigger the Check Engine light.
A loose gas cap can trigger the Check Engine light.
A fault O2 sensor can trigger the Check Engine light.
A Mass air flow sensor problem can trigger the Check Engine light.
Perished Spark plug wires can trigger the Check Engine light.
A blown  Catalytic converter can trigger the Check Engine light.
Low oil pressure or overheating can trigger the Check Engine light.
Sporadic engine misfiring can trigger the Check Engine light.

  

Hall Sensors

VW POLO

Volkswagen has always had an upstanding reputation (other than for the emission scandal) for manufacturing quality vehicles at affordable prices. One such car is the VW Polo hatchback which has also become one of the most popular cars in South Africa, and it’s really not hard to see why. The VW Polo is a compact car, but when driving it, it somehow feels larger, somewhat like its bigger brother - VW Golf. Should you buy one, you would certainly agree that the VW Polo has universal design appeal, that it has good performance, decent fuel economy and is sold at a relatively affordable price. 

Hall Sensor Hall Effect Sensor Switches A3144 / 3144E / OH3144E
in a TO-92UA 3 pin SIP package can be bought for as little as 1 USD

Volkswagen has capitalize on this winning formula for years and has given us plethora of Polo's to choose from ranging from the Polo Trendline, to the Polo Comfortline, to the Polo Highline, not forgetting the Polo Cross and Polo GTI which comes in 3 and 5 doors classic and hatchback versions. Engine capacities and engine technologies range from 1.2 TSI 66kW and 1.4 TDI 55 kW for the Trendline,   1.4 TDI 77 kW, 1.2 TSI 81kW for the Highline  and 1.2 TSI 81kW Highline DSG, to  1.0 TSI 70 kW BlueMotion. The sedan or VW Polo Classic comes in  1.4 & 1.6 trendline, 1.6 comfortline / tiptronic, 1.9 tdi highline (74kw)  and 2.0 highline (85kW).  There is even a GTI (Grand Touring Injection), a FSI (Fuel Stratified Injection), TSI (Turbo Stratified Injection) and a TDI (Turbocharged Direct Injection), to choose from. 

Clearly there's a Polo out there waiting for you! Having said that, owning a Volkswagen doesn't come without challenges, personally I think the biggest challenge is more likely than not the dreaded EPC light that triggers at the most inopportune times. The EPC circuit has several sensors that feeds into the ECU among them Hall sensors. From my experience hall sensors tend not to like heat, even though their specification sheets rates them above the requisite heat range.  

This datasheet gives you a good idea of a hall sensor's specifications 

Hall sensors are pervasive throughout modern day cars. Hall sensor, aka Magnetic sensors essentially converts magnetic pulses into electrical input signals for processing by electronic circuits. Magnetic sensors are solid state devices meaning there are no mechanical moving parts inside, its all electronics taking place in a sealed chip of silicon, making them immune to vibration, dust and water. This makes them popular choice by electronics designer engineers for several types of application ranging from  distance sensing, to velocity sensing, to position sensing, to  speed sensing, to directional movement sensing etc.

Hall sensors are used for angular position sensing of the crankshaft to determine the firing angle of the spark plugs. They are used for magnetic position sensing in EGR systems. They are used for wheel speed detection for the anti-lock braking system - (ABS) and speedometer. Throttle bodies with DC motors use hall sensors for position sensing. Hall sensors are also used to determine the position of the car seats and locking of seat belts. Hall sensors are employed in automatic transmissions as magnetic neutral position switch, as actuator sensors, as speed and direction sensors, for gear detection and clutch position sensing. Hall sensors are used as engine speed sensor and also as the vehicle speed sensors.  And the list goes on.

The following images depicts a hall sensor replacement inside the distributor of and Audi 5-cylinder engines 2.0 - 2.3. As can be seen the the wires have distinct colours , the red wire is +5V / 12V supply, the black wire is negative / ground and the yellow wire is the output of the hall sensor / sender.

There is space under the black plastic holder where the wires connect to the hall sensor.

Multi purpose hall sensor for automotive use, but the military spec hall sensor is a better option

The sensor is replaced, solder joints covered with fiber glass sleeving then epoxied into place.

Hall sensor plate reassembled

Hall sensor assembly fitted into distributor housing

As I mentioned in a previous blog, Hall sensors don't like heat and tend to malfunction when they get too hot. My first experience with hall sensors were when I was working as an electronics engineer for A Television and Video repair company. A video machines that employed a hall sensor in its take up clutch stopped working due to overheating.  By squirting the hall sensor with a blast of servisol rapid cooling spray, it started working again. I repeated this exercise a few times to make certain that the hall sensor was the culprit, after replacing it, the machine worked just fine. 

Then I also had a problem with my Opel Kadett 1.8 GSI  when driving in peak hour traffic. It would switched off and refused to start.  But after allowing the engine to cool, it started just fine and would be perfectly ok for days until I got stuck in bumper to bumper peak hour traffic again. The dealer had a field day with my car, telling me that they repaired a bad earth under the dash board, only to find out in peak hour traffic that they misdiagnosed. Then I was told that the loom was replaced, then I was told the ECU was replaced and finally that a hall sensor inside the distributor was replaced. This fix the problem once and for all. The images above is for the same symptoms on a Audi  2.0L 5 cylinder.  As perfect as hall sensors are for most applications, where there is excessive heat, they will misbehave.  Perhaps hall sensors mounted in heat intensive spots like the engine speed sensor, should be designed with a heatsink or have its own cooling fan. This advice is as relevant for current model cars as it was for the Audi 2.0L 5 cylinder.

Volkswagen Polo

Volkswagen Polo

The Volkswagen Polo Vivo is undoubtedlty the most popular, as well as the  best-selling car is South Africa. Looking at the top ten vehicles sold in South Africa, VW Polo Vivo takes first place, the Volkswagen Polo takes third place and the Vw Golf takes tenth place. Looking at the frequency of problems encountered with Volkswagen vehicles  in general, it appears that the VW Polo 2002-2009 models are far more reliable than the VW Polo 2010—2016 models. These models are prone to EPC problems and several Polo owners have complained that they encountered EPC problem with their cars with as little as 700km on their clocks.

The most troublesome generation 5, VW Polo seem to be the 2011 model, but the 2012 model takes the cake for the annoying knocking sounds coming from the suspension when going over speed bumps and pot holes.  But this knocking sound isn't unique to the Polo 2011 and 2012 models, it also affects the Golf Mark 7, the Volkswagen Transporter T5 and Polo GTI, etc.

It seems that somehow the strut mount bolts in the engine bay of these Volkswagens haven't been torqued properly. The rattling and knocking noise coming from the shocks occurs when driving over pot holes  or over speed humps, especially when the shock is fully extended or when driving slow.  In some cases the noise comes from coil-over assembly. These coil-overs squeek and creak at random and sometimes the rear ones squeak worse than the front ones. We found by removing the damper adjustment knob and tightening the 17 mm nut in the middle of your strut top,  and   holding the centre with a 7 mm allen key,  the noise is  somewhat reduced but is very disconcerting since these models are relatively new cars. 

Its probably best to re-torque these nut between 45-60 ft/lbs with a correctly  calibrated torque wrench. In my opinion there should have been a total recall on VW Polo 2010—2016 models for this problem. 

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?  

Is EPC safe?

IS EPC SAFE?

The Electronic Power Control Circuit with its EPC light virtually has every motorist annoyed globally. Most motorists seem to be up in arms over this "idiotic warning light". Yes, this is exactly what several clients have called it because they believe manufacturers added it into cars as  a "cash cow" measure, which the dealer will reset by just pressing a button and charge then through there noses. This is really not the case because there are so many dealer's mechanical workshops that have no idea how to fault find nor repair and EPC fault. Motorists have even gone as far as saying the the EPC circuit is an unnecessary addition, as the tried and tested Otto Cycle internal combustion engine has worked perfectly for at least a hundred years without it.  

Without question, the EPC light is probably the most misunderstood dashboard light plaguing motorist the past two decades. However the EPC circuit is in fact a safety feature that few seem to appreciate. But is doesn't work in isolation, it is a sub circuit of a the ECU circuit. The ECU overseas the running of the running of engine at its peak whereas the EPC circuit is specific to the torque circuit - whatever propels the vehicle and safely stops the vehicle!

For example, in older cars that used a physical cable to control the throttle; it was prone to fray and could easily get stuck whist driving at high speed. This actually happened hundreds if not thousands of times, hence an alternative was imperative. When releasing the accelerator pedal with a frayed cable the engine would remain at a high rev and make braking difficult if not impossible. Restated, an accident in the making. This will never happen with cars fitted with EPC because it uses drive by wire - which in effect is an electronic throttle control,

Some Volkswagen vehicle problems makes driving in traffic very difficult let alone dangerous due to loss of braking & steering assistance. Case in point, when the ABS warning light comes on, its more often than not a melted fuse located on the battery cover that dies from metal fatigue or caused by faulty  or  intermittent connection on the wheel rotation sensor wiring.  Or if one of the brake light burns out, the EPC circuit would determine that the car is not in a "roadworthy condition" and instruct the ECU to disables propulsion so that the necessary repairs can be effected.

The EPC circuit monitors several sensors and when anyone of them go out of whack, the EPC kicks in, to the rescue of the driver by sending the car into limp mode. Admittedly not everyone shares the sentiment that "limp mode" is a safety measure because if appears to causes more feelings of frustration than feelings of safety. There are tens of thousands of motorists who would testify to the latter, myself included. I experienced  loss of power whilst driving on the freeway with a large trucks behind me, that almost wiped me out if I hadn't swerved out of its way just in time.

I'm almost certain you've had a similar experience with your Volkswagen. My sister had such an experience with her grandchildren in the car ad she swore she would never drive a Volkswagen again.

EPC ELECTRONIC POWER CONTROL

EPC ELECTRONIC POWER CONTROL Q & A

Common causes for EPC warning light illumination

Over the past few weeks numerous questions came pouring in, really fast and furious, most of them at a loss about the EPC light on their vehicles. Below are a few of the VW owner's questions, accompanied by my answers that may have solve their EPC light problems. However, the symptom they present may be similar to your car's symptoms but the cause may not be identical, so therefore the answer may not exactly fit your problem, but it could at least but you the right track. If  you suddenly see the yellow EPC dash board light illuminate on your Volkswagen, Polo, Golf, Kombie, Jetta, Passat etc. don’t panic. 

The EPC light is amer/orange because it's an informational /warning light, whereas a red dashboard light calls for immediate attention, for example when the the oil or water dashboard lights comes on. EPC stands for Electric Power Control (EPC), and  is a computerized ignition and engine management system that can alert you to a potential engine malfunction, as well as alert you to a variety of engine issues, though most of them are fairly simple to diagnose and repair. Bearing  in mind other systems such as stability  control and cruise control can also have an effect on the EPC system.

QUESTION:- 

My VW Golf VI 2010 model shakes when I accelerate, then it suddenly looses power and the EPC light illuminates. Can you please help. What could be the cause of this  and please tell me how to fix it.

ANSWER:-

Most VW engines have a flat-plane crank, meaning the inner two pistons move up and down together, in opposition to the two outer pistons, each providing 90 degree crank propulsion. When one of the cylinders are not doing their portion of the work, the crank is unbalanced and will cause the entire car to shake. This normally happens when either an injector or a coil on one of the cylinders is misfiring. Since the EPC circuit monitors the engine torque, it will illuminates the EPC light when it diagnoses that 25% of its torque is lost. By restoring the 25% torque by replacing the faulty component, either the coil or the injector by a process of elimination, the shaking will stop. 

Then again, I experience severe shaking on my Polo 2.0 one day, for some reason o the other, two blades of he radiator fan  snapped off and the centrifugal force of the two remaining blades shook my entire car really violently. Its the first time I experience something like that and at that moment in time I got such a fright, my heart was pounding in my throat.

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QUESTION:-

I have a Golf Polo 2012 model that's been to the agents for regular diagnostic tests because its been more than a year that they've been trying to resolve the “EPC” light  problem.  The following items have been replaced but the light still comes on -
Ignition coil, Throttle Body, Accelerator pedal, Four injectors
Cambelt kit, RPM sensor .

ANSWER:- 

Since so many components have been replaced, I would suggest you upload a diagnostic scan so that I can analyse it because the above looks like guess work. There are so many things that can trigger the EPC, but don't replace anymore components until you've checked:-

1) The rubber hoses to the MAF for cracks,
2) Cleaned out the tar-like deposits in the throttle body,
3) Cleaned the idle speed control and butterfly valve with Wynn’s Throttle Body and Air Intake Cleaner, 
4) Performed a throttle body adaptation, 
5) Checked that the knock sensors are properly torqued,  
6) Checked for the correct spark gap on your spark plugs, 
7 Checked that your engine temperature coolant sensor works, 
8) Checked that your fuel cap seals properly, 
9) Checked that your fuel pump isn't noisy, because if it is, its probably pumping under the required pressure. 
10) Checked the wiring loom connecting to the pencil coils and the fuel injectors for intermittent contact. 

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QUESTION:-

Please tell me why does my Polo's engine switches off while I'm driving? When I try to accelerate there's no power and when I looked at the dashboard, the  EPC Dashboard Warning Light is on. That's when I realize the engine is not running. But thereafter my Polo wouldn't restart, not until  it cooled for a while. Then my polo will then drive perfectly normal until the next time the EPC light comes on again.

ANSWER:-

This sounds very much like an  Engine Speed Sensor problem. Normally when they do go faulty the car will not start at all.  It is common for the EPC light to come on, by which time the engine died and after about 2 hours everything is back to normal. However its seems like your Polo's sensor is just starting to give trouble. This is a hall sensor, that generates a waveform whenever it senses the rotational magnetic pulse. But when it gets too hot, it starts to fail. I've had hall sensors located inside the distributor go faulty on Opel Kadett GSI due to engine heat in peak hour traffic but after it cools down, the Opel starts and drives normal.  It seems like hall sensors don't like heat.   

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QUESTION:-

I had my Volkswagen cc R-Line's  brake pads replaced after 48,000 kilometers  but now every time when I accelerate the EPC light comes on and there's no power. I'm totally miserable because the car is now useless. Can you please shed any light on this matter?   

ANSWER:-

Dude, its more likely than not that you've picked up a wheel speed sensor problem from your mechanic. One of two things, either the plug to the ABS wheel sensor isn't making good contact / the wire from the sensor is broken off or the gap between the ABS sensor and the disk is wider than it should be. It's very unlikely that the sensors are faulty because it probably worked fine before your mechanic replaced the pads. A telltale sign is that your speedometer isn’t working because the front sensors are also the input for the speedo.

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QUESTION:-

I was cruising on the freeway and suddenly the power just cut out and there was no more acceleration and the EPC light went on. I thaught my VW Jetta ran out of fuel because the fuel gauge was on empty but it didn't because I could still drive it slowly. but it wouldn't revv up.  I took it to the agents who said it was caused by driving with a little fuel in the tank. But now the same thing has happened to me four times thereafter. What can I do because the agents say there is nothing wrong.

ANSWER:-

If truth be told, your intank fuel pump must have overheated when you were driving with an empty tank. Remember the fuel pump is cooled and lubricated by the fuel in the tank and when there is no more fuel to cool and lubricate, the pump can overheat.  Also, if there is debris in the tank, it can block the filter or pipe attached to the pump. Since this is a low pressure pump  it won't have force to clear the debris and wont be able to feed fuel to the high pressure pump driven by the camshaft. It's probably best to have your fuel line cleared under pressure alternatively replace the fuel pump.

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QUESTION:-

I have an Audi A4 with a early model 2.0T engine. For the past few weeks starting from cold in the morning has been a problem but since yesterday, it seems to have lost all power it power and the EPC light is on. With the pedal to the floor in any gear, the rpms increase but the car just won't pickup speed.  

That seem to a common issue with the older Audi A4 models. It's normally the high pressure fuel pump pawl that's busted, which probably destroyed the lobe on the camshaft as well. Sometimes the pressure of the camshaft hollows out and destroys the cylinder head. Check the high pressure at the output of high pressure pump, it it's low then  it's definitely the pump and camshaft combination.

Volkswagen and Audi EPC

Volkswagen and Audi EPC

The Internet is a huge repository of  information, some useful  and some not so useful, or more to the point, useless. But, there is so much of both, duplicated and reechoed  in posts like auto-facts, axleaddict, youfixcars, and motor forums by so many individuals. There is nothing worst than being led up the garden path by some ignoramus who knows squat about electro-mechanical engineering technology when you are desperately looking for answers. To reduce that from happening, I decides to bust some of the myths related to VAG cars that are being echoed over and over and over.

EPC can be a bitch to repair.

Myth 1
Here's the first myth from someone on Yahoo Answers, relating to a 2012 VW Polo. "You can clear fault codes by disconnecting your battery for a while".  And here's another, "just disconnect the battery on your Audi A3 for a little more than 10 seconds and your fault codes will be  gone"! 

Myth 1 Busted
Though the above is true for pre-1996 vehicles fitted with OBD-I, disconnecting the battery on any car manufactured post-1996 fitted with OBD-II will definitely not delete any fault codes because the ECU stores all DTC (Dignostic Trouble Codes) aka fault codes codes in its  non-volatile memory.  What it will do, is reset the cpu / timer. The term non-volatile memory is generally used for all types of solid state memory, meaning memory that doesn't need its contents refreshed periodically. 

However, the ECU also stores learnt values and basic settings, like for example the Fuel Control Learning Adaptation Values and the Kick-Down Position of the Accelerator which is needed by the automatic transmission. This data and your car's radio code is not stored in non-volatile memory and will undoubtedly be erased when the battery is disconnected.  Once the battery is reconnected, the adaptation process needs to be done which will enable the ECM to learn the new settings for the Drive-by-Wire electronic throttle  valve and store it. If you didn't save the radio code you have to go to a VW / Audi dealer with your VIN and they may be able to give it to you.

When you disconnect your car's battery, the ECU detects the loss of battery power and registers a DTC in the ECU's non-volatile memory to that effect. This record can be seen after the battery is reconnected and a  diagnostic scan is performed.  It would look something like this,

2 Faults Found:
00532 - Supply Voltage B+ 
            07-10 - Signal too Low - Intermittent

01598 - Drive Battery Voltage 
            07-10 - Signal too Low - Intermittent

Removing the negative terminal of the battery isn't all bad, it does have the advantage  of resetting  the system's ECU safety watchdog timer. A safety watchdog timer (WDT) is responsible for periodically generating a system reset in the event of a software glitch. This one of a kind CIC61508 safety watchdog timer is ASIL-D (Automotive Safety Integrity Level D) approved,  where level D refers to the highest classification of initial hazard against the risk of injury as defined within ISO26262 automotive industry standard.

Infineon Safety Watchdog timer 

Pressure Sensors

Myth 2
There are pressure sensor in the VW and Audi engine block that causes an EPC light to come on and make the car go into limp mode.

Myth 2 bustedYes, there are pressure sensors in both VW and Audi engines but they not fitted into the block and should not be mistaken for than for knock senors that are screwed to the block. Faulty or loose knock sensors can cause the EPC light to come on and send the car into limp mode.  The baro sensor measures the ambient air pressure and has a effect on engine performance altitude dependent.  The supercharger boost pressure is controlled via the regulating flap control unit Intake manifold pressure sensor/MAP sensor (MAP = Manifold Air Pressure) which can cause the EPC light to come on and send the car into limp mode. The high-pressure fuel pump delivers fuel at a pressure of up to 150 bar and any drop in this pressure can cause the EPC light to come on and send the car into limp mode. Common problem with loss of pressure is the fuel filter. Loss of oil pressure can cause the EPC light to come on and send the car into limp mode. Lastly there is high system pressure in the cooling system at high revs and sudden loss of this pressure can cause the EPC light to come on and send the car into limp mode.

Myth 3
EPC light usually means that the Electronic Throttle Body needs replacing and reprogramming.  

Myth 3 busted It is advantages to perform adaptation on the throttle body, before attempting to replace it with a new throttle body . Often times replacing it makes no difference and normally turn out to be the wiring harness connectors to the throttle body that's defective.   Disassemble the three electrical connectors around the throttle body clean  this inside of the connectors with circuit cleaner and reassembled. Also check for vacuum leaks, especially pressure regulator hose and the small pipes connected to the intake-manifold before replacing anything.

Myth 4
Epc light is mostly known to come on when there is emissions problems. 

Myth 4 busted This is incorrect because the 'check engine light' is specific to emission related problems, however The EPC light may also come on if the emission related problem affects the engine torque. So repairing the emission related problem first would in most cases reset both the EPC light and the 'check engine light'.

Sensors associated with EPC

Extensive safety measures have been designed and implimented 
in both the hardware and software of Audi and VW.  In most cases dual sensors are used for continual self-checking of signal plausibility. A safety watcg dog timer is integrated in the Motronic ECM to constantly and continually monitor the processor for correct and proper operation. Some of the sensors are listed below.

Fuel Pressure Sensor G247
Low Fuel Pressure Sensor G410
Oil Level Thermal Sensor G266
Heated Oxygen Sensor (HO2S) G39
Heated Oxygen Sensor (HO2S) 2 G108
Oxygen Sensor (O2S) G130 &  G130
situated behind 3 Way Catalytic Converter (TWC) G130
G186 Throttle Drive  (EPC))
G187 Throttle Drive Angle Sensor 1  (EPC))
G188 Throttle Drive Angle Sensor 2  (EPC))
Engine Speed (RPM) Sensor G28
Mass Air Flow (MAF) Sensor G70
Throttle Position (TP) Sensor G79
Accelerator Pedal Position Sensor 2 G185
Clutch Position Sensor G476
Throttle Valve Control Module J338 
Throttle Drive Angle Sensor 1 (EPC) G187
Throttle Drive Angle Sensor 2 (EPC) G188
Camshaft Position (CMP) Sensor G40
Camshaft Position (CMP) Sensor 2 G163
Engine Coolant Temperature (ECT) Sensor G62
Engine Coolant Temperature (ECT) Sensor G83 (on radiator) 
Knock Sensor (KS) 1 G61
Knock Sensor (KS) 2 G66
Brake Light Switch F

Automotive Electronic Components

Automotive Electronic Components

Admit it or not, we all love the new creature comforts of our modern day cars, all of which have become increasingly sophisticated.  Those seat warmers in the cold of winter, the climate control in mid summer, the air suspension on those bumpy roads, the infotainment systems with integrated GPS so that we never get lost again; and the on-board video player for those times we had to patiently sit and wait in our cars for our loved ones. ECU controlled fuel injection put an end to idling the car in the morning to get it to the appropriate operating temperature. Power steering and assisted parking makes both driving and parking a breeze. ABS and traction controls ensures that your car stops and corners without incident. 

Not to mention cruise control, the increased horsepower, the additional  safety features and the overall improved spatial comforts. And the list goes on. All of this was made possible by electronics, in the name of safety. Safety in the form of Safety Restraint Systems (SRS), Front and side airbags, early crash sensors and active front seat head restraints, to  mention but a few. 

On-Board Modules

Electronic engine management systems, carputer modules, telematic systems and other electrical components constitutes a sizeable percentage of our cars, collectively affording us the aforementioned comforts and conveniences. Besides, modern cars are loaded with code; and the number of electrical components in modern cars are on the rise, constantly and consistently increasing in number, and their failure can more often than not affect our driving safety. These electronic components can easily malfunction, either due to water ingress during wet weather conditions, or due to excessive vibration due to bad road surfaces, or just through general wear and tear. Most of these components are cheap and relatively easy to repair and replace but isolating the correct one can sometimes be trying. In a nutshell, modern day cars are seriously complicated, since they are not just computers on wheels but entire computer networks on wheels. Be that as it may, it is a well known fact that computers do crash, software have glitches and networks go off-line.

How safe is safe?

But, the million dollar question remains; are these electronic devices really safe or are they as safe as the car manufactures would like us to believe they are.  How safe is it when you're overtaking on a single lane highway at 100km per hour and the car goes into 'limp mode' or the engine just switches off and refuses to restart?  How safe is it when the steering wheel airbag explodes directly into your face for absolutely no reason? Its air pressure wave that's louder than a gun, is bound to temporarily deafen you and the smoke enveloping you would certainly disorientate you. These factors can contribute to you loosing control of the car through no fault of your own or even loose your life.  

How safe is it when you suddenly and momentarily loose steering control at high speed or whilst driving in fast moving traffic when your car doesn't react to your steering direction?  Or, how safe is it when your steering wheel suddenly goes stiff when turning (temporary loss of power steering)? How safe is it when your car randomly starts to jerk and switches off on a deserted road at night? 

How safe is your VW really, considering certain Jetta, Golf and Audi A3 models are being recalled for fuel leaks that can cause potential engine fires. Case in point, German supplier Continental Automotive GmbH has been supplying fuel tank polymer flanges that crack to five OEM parts supply companies at least 11 auto makers, VW, Audi and Porsche included.  What this means is that 
there are millions of cars of all makes and models that may have leaking fuel issues as we speak.

Electrical sub systems

As mentioned above, modern cars, can have as many as 200 small embedded electronic control units, better known as  (ECUs). Each module is in fact a fully fledged computer in its own right, overseeing one subsystem. Collectively they  have several functions, ranging from controlling the engine and or transmission, to controlling the immobilizer, to controlling the air bags, to unlocking doors, to controlling the radio, to managing the ABS, to managing the cruise control and such like. 

Most of these computer modules have input switches and or input sensors that can detect variables such as temperature, air pressure, braking, steering angle, voltages. All these computers are connected to a centrally networked  CAN bus that carries constantly varying data between them, in order to manage the car as it is being driven. The upside of this, is that the car can virtually drive itself but the downside is that when some essential module does go faulty, it would most likely shuts the car down which may also turn out to become an expensive repair.

Automakers are becoming more like 
assemblers and less like manufacturers

Essential components like headlights and spark plugs, ignition leads, wiring harnesses, relays and switches  can often be the first to go, but they are more electrical than electronic. Whereas the following list of sensors and actuators are totally electronic.

Air mass sensors (MAF) - electronic
Camshaft Position sensors - electronic
Crankshaft Position sensors - electronic
EGR Valves  - electronic
Knock sensors - electronic
Lambda (oxygen) sensors  - electronic
Throttle position sensors  - electronic
Wheel speed sensors  - electronic
Ignition Coils  - electronic
Glow Plugs  - electronic
Coolant temperature sensors  - electronic
ABS  actuators  - electronic
Injection valves - electronic
Solenoid valves - electronic
Anti-theft alarm  - electronic ... and the list goes on.

Since Automobile production requires several thousands of parts, most of these parts are not manufactured by the car maker but are supplied by auto suppliers. Hence automakers are becoming more like assemblers and less like manufacturers because Auto Megasupplier's  contributions have drastically increased from about 60% in the mid '90s to above 85% in 2017.  Among these auto megasuppliers are companies like:-

Robert Bosch supplies (Gasoline and diesel systems, chassis system controls, electronics,  exhaust gas turbochargers, steering systems, starter motors and alternators,   etc), 

Draexlmaier Group (wiring harnesses,  interior systems, cockpit and door modules, etc.),

Royal Philips Electronics (Lighting, car radio integrated circuits, liquid crystal displays, etc.)

Infineon Technologies (Microcontrollers, intelligent sensors; power semiconductors, etc.)  

Hella ( Electronic & lighting components, etc.)

DuPont Automotive (polymers, elastomers, specialty chemicals, lubricants, refrigerants, etc.) 

SKF Automotive ( Bearings, seals, clutch assemblies, SKF Automotive drive-by-wire systems, etc.) 

Valeo SA (transmissions, Micro hybrid systems, etc.)  

Magneti Marelli (Lighting, powertrain transmissions, electronics, suspension systems,  shock absorbers, exhaust systems, plastic parts, etc.)

Continental AG (Instrumentation, stability management systems, chassis systems, safety system electronics, telematics, powertrain electronics, interior modules, etc.) 

Eberspaecher Holding GmbH (Silencers, catalytic converters, particulate filters, manifolds, vehicle heaters, electrical vehicle heaters, electronics, climate control systems, etc.)

CITIC Dicastal Co.  (Aluminum alloy wheels, aluminum casting parts, etc.)

Mobis North America (Chassis, cockpit & front-end modules; ABS, ESC, MDPS, airbags,  LED lamps, ASV parts, sensors, electronic control systems, hybrid car powertrains, parts & power control units, etc.)

That being said, there are so many of these components from auto suppliers that are troublesome. For example, batteries, starter solenoids, diodes and alternator voltage regulators and relays. Considering that the alternator is the heart of  your vehicle's electrical system and that the electrical load has substantially increased due to the glut of extra electronics, I would think that some manufactures would at least have a second alternator for redundancy. Even perhaps a redundant network so that an alternative data path is  available if the wiring harness goes faulty. Or even dual temperature sensors, or dual camshaft sensors, etc. It would do marvels for reliability.

Volkswagen is recalling some 766,000 cars globally for a software upgrade to their "anti-lock braking system".

Volkswagen is recalling 8.5 million diesel cars across the European Union  due to the "emissions scandal".

Volkswagen is recalling some 90,000  gasoline powered VW Beetle, VW Golf, VW Jetta and VW Passat with 1.8T or 2.0T engines sold between 2015-2016, because the rear camshaft lobe has the tendancy to unexpectedly snap-off from the camshaft resulting in "loss of vacuum to the brake booster", implying inefficient braking and an increased risk of a crash.

Volkswagen recalls some 280,000 cars for fuel leaks.

Honda recently recalled 1.2 million  from the 2013-2016 model Accords years, citing 'faulty battery sensors'.


Ford South Africa recalled 2.0-litre diesel-powered Kuga SUVs to resolve a potential "brake problem".