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.

WHAT IS A VW EPC WARNING LIGHT

What Is a VW EPC Warning Light

The EPC warning light is an instrument cluster based LED found on all Volkswagen, Audi, Seat and Skoda vehicles fitted with a drive-by-wire system and EPC stands for Electronic Power Control. However the EPC warning light is not exclusive to these VAG cars, most other motor manufacturers also have them, since it's legislated to be part of the OBDII system. This EPC light when lit displays the letters EPC and primarily warns the driver that there is problems in the engine's torque system - (acceleration system). The reason why the EPC turns on, problem could be many, among which are the vehicle's knock sensors, its throttle system, its cruise control, its mass air flow system, its engine speed verification system or any of the other associated systems that cooperate in the drive-by-wire schema. 

When this EPC light comes on, the vehicle’s throttle valve (butterfly) may be limited in order to protect the engine from damage. It prevents the engine from revving above 2000rpm. This is known as limp mode and the ECU permits just sufficient power to drive the vehicle to a service center for repairs. To remedy the problem, the vehicle’s ECU should be scanned with an automotive diagnostic too, in order to extract the DTC's related to the torque problem.  Cars with an accelerator cable are also fitted with an EPC light but the ECU software is quite different, yet the overall principal remains the same.

All Volkswagen (VAG) vehicles have a whole array of dashboard warning lights in their instrument panels, specifically designed to alert the driver to any vehicle malfunctions or problems. In fact so does all most modern day automobiles. Having said that, it is only a matter of time before these lights start lighting up. Invariably and inevitably all cars will breakdown at sometime or the other but its nice to be warned about a mechanical problem before it actually occurs. For example, having a low coolant level light or an low engine oil-level light flash at you, accompanied by an audio alert is a blessing because complete loss of either coolant or engine oil could result in a very expensive repair. 

The one warning light that puzzles most drivers is the VW EPC warning light. Driver often ask, what is the VW EPC warning light? Like I've mentioned above, it is a bright yellow dashboard light with the letters EPC inscribed in bold.it  When lights-up to draws your attaention to a potential malfunction in the EPC system. When it lights up whilst driving and the trouble is related to a safety issue, the car will more than likely go into limp mode. This may sound quite serious but in most cases it's not. There are several reasons why EPC Dashboard Warning Light turns on, but through a process of elimination the cause can be tracked down fairly easily. 

The Engine Speed Sensor is  known to cause the EPC light to turn on. The engine speed sensor is a proximity magnetic transducer counting the revolutions of the flywheel / crankshaft and sends a steady stream of pulses to the ECU. So when this stream of data is interrupted for whatsoever reason for only a fraction of a second, the ECU  detects this and turns on the EPC light and cuts power to the engine. It does this to protect the engine from damage. 

If you have a scan tool, check for DTC errors. The following error code, 17745 /P1337, 17746 / P1338, 17747 / P1339 and 17748 / P1340 are the troubles codes that provides a  tell tail sign that the engine speed sensor is either loose or faulty, hence the car's engine cuts-out whilst driving and the speedometer is inoperative.  But in some cases the engine will start again. When this symptoms repeats itself often, you should know it is time to replace that pesky engine speed sensor.

The Accelerator Pedal itself is often the main culprit that causes EPC problems. A telltale sign is that the engine idles a lot faster than it aught to. To verify this, physical pull the accelerator pedal away from the floor board while the car is idling. If it reduces the engine's revs back to normal, then it is time to replace it, because the potentiometers that's built into the the accelerator pedal, have gone faulty. Accelerator pedal problems are numerous and the following DTC, 16504 / P0120, 16505 / P0121, 16506 / P0122, 16507 / P0123, 18038 / P1630, 18039 / P1631, 18040 / P1632, 18041 / P1633, 18042 / P1634, are linked to accelerator pedal errors. 

Mass air flow sensor is another engine component that can cause the EPC light to turn on. Cleaning the  mass air flow sensor with compressed air does often solve the problem but if the issue persists, its time to replace mass air flow sensor. But before changing it, check to see if any of the rubber hoses in its vicinity isn't perished. An leak in Air Intake System wil allowing air unmonitored to enter the intake which will throw a P2279 / 15093 error or a P0068 / 15101 error.


The Throttle body is by far the most common cause of an EPC problem though in many cases it is not the throttle body that's at fault but rather that it the needs to be recalibrated (adaptation). The scan codes like P2135 / P2136 / P2137 / P2138 / P2139  and P2140, will give a  good idea as to whether or not the throttle body require replacement.  But in many cases it turns out to be  wiring harness issue. The plugs that connects the throttle drive motor and the throttle position sensors is fairly troublesome ad should be checked before throttle is replace.

The Brake light switch can also cause the EPC light to come on because the torque control circuit uses the brake light signal as a ECU input signal when the car decelerates.  

The Injectors and the Ignition Coils can also cause the EPC light to turn on. I've heard that an incorrect spark gap on the plugs can also cause an EPC problem but haven't experienced it yet.  Driving with very little gasoline in the tank can also cause the EPC light to turn on because the high pressure fuel pump may lose pressure which then notifies the ECU to inhibit the torque circuit and switch on the EPC light and make the car go into limp mode.

I've experienced the Knock Sensor turn on the EPC light. Spirited driving also turns on the EPC light.

So as you can see there are several things that can cause an EPC fault.  This is not a complete list of EPC problems but as new ones are identified, I will post them.  The following questions prompted me to write a synopsis of what an EPC light is!

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KNOCK SENSORS

KNOCK SENSORS

Gone are the days when you could fix your own car with simply logic. Today you require digital logic, a scan tool  and a tech savvy mechanic to make sense of the latest cars because they are all very precisely controlled by electronic circuits. The Engine Control Module is just one such circuit and largely depends on several of its sub-circuits and associated automotive control modules to achieve the precision needed to propel the latest engines using high octane fuel, and burn it stoichiometrically in order to deliver the performance expected from these modern cars. But this is easier said than done because these sub-circuits and associated control modules rely on a number of inputs sensors and actuators distributed all over the engine and the car in general, to successfully control of the crank synchronous path.

In order for the ignition sub-system to function optimally for example, it requires feedback information about what is presently happening in the engine so that it can take corrective action if needs be, in real time. Likewise the fuel mixture sub-circuit can only determine if the mixture is rich or lean from the feedback information, then take corrective action to increase or decrease the quantity of fuel based on the amount of oxygen present. Like wise the crankshaft timing sub-circuit depends on feedback information and maintain a constant torque. Yet all three these ECM sub-circuits works very closely in conjunction with one another and other sub-circuits to achieve optimal performance. 

Restated, the ECM is in control of the torque and torque reduction circuits, which just happens to annoy the arse-mousse out of Volkswagen, Audi, SEAT and Skoda owners. It is commonly referred to as the EPC -Electronic Power Control. Essentially EPC is limp mode's best friend and vehicle owners worst enemy.  ECM torque reduction is handled via the crank synchronous path, and involve the  ignition system sensors, the knock sensors, and fuel mixture both short trim and long trim. 

Input signals are needed for calculating precise ignition timing:

1) Engine Coolant Temperature Sensor (ECT)  

2) Engine Speed Sensor (RPM)  

3) Throttle Control Valve Sensor  

4) Camshaft Position Sensors

5) Knock Sensors  

6) Accelerator pedal Position sensors


By monitoring the Engine Coolant Temperature Sensor (ECT), the ECM varies the parameters of the engine as it heats up and maintains it when it has reached the correct operating temperature. 

By monitoring Engine Speed Sensor (RPM) the ECM can determine how many times the coils misfires per 1000 revolutions and how many times the injectors fail to deliver fuel. 

By monitoring the Throttle Control Valve Sensor the ECM can calculate the torque compared to how wide the throttle opens. 

By monitoring the Camshaft Position Sensors the ECM can better determine the exact time when the valves close and the exact point of ignition. 

By monitoring the  Knock sensors the ECM decides whether detonation is bad enough to take action, either  to retard / advance the engine or reduced the torque and consequently prevent engine damage. 

By monitoring the Accelerator Pedal Position sensors it can determine synchronicity between the position of the accelerator pedal when depressed and the throttle control valve and and discrepancy outside of its normal parameters will reduce the torque. 

KNOCK SENSORS

Knock sensors are very important to the overall engine torque because they detect combustion knocks in the individual cylinders. This is common when high octane fuel self ignites  which is generally known as knocking (detonation) or pinging (pre-ignition).
Knock sensors are piezo-electric components acts something like microphones do, but instead of picking up sound,  they detect vibrations in an engine which are needed by the ECM to correct the combustion process in the event of detonation or pinging.  This allows the ECM  to "retard" the engine so that it would work with different quality fuel. This implies that lower octane fuels are more prone to knock than higher octane fuels. It is therefore imperative to use the correct octane fuel prescribed for your vehicle since failure to do so can cause the EPC light to turn on and cause the vehicle to enter into limp mode.

TESTING KNOCK SENSORS

Four and six cylinder engines have 2 knock sensors each. Knock sensor 1 monitors the even bank of cylinders while Knock sensor 2 monitors  the odd bank of cylinders. W8 and W12 engine have 4 knock sensors each.  Knock sensor 1 monitors  cylinders  1 & 2, Knock sensor 2 monitors  cylinders 3 & 4, Knock sensor 3 monitors cylinder 5 & 6, and  Knock Sensor 4 monitors cylinder  7 & 8. Knock sensors are mounted directly on the crankcase and must be torqued. Failure to torque a knock sensor may cause it to malfunction and pickup engine vibrations as well as detonations.

The plug for Knock sensor (KS) 1 is normally green and it monitors cylinders  1 & 2, whereas the plug for Knock sensor (KS) 2 is normally grey and it monitors cylinders 3 & 4. Knock sensors are three pin devices with  Pin 1 = Signal, Pin 2 = Ground and Pin 3 = Shielding. Using a multimeter measure the resistance for "short circuit" between pins 1 and 2, then 1 and 3, then 2 and 3 at the Knock sensor connector. This measurements should always read infinity (open circuit).  If short circuit, replace knock sensor and make sure that it is correctly torqued to the crankcase.  Also check the wires for short circuit. If short circuit, replace. If a oscilloscope is available, connect it between pins 1 & 2 of the knock sensor. Tap the knock sensor lightly with a wrench, this should produce a fairly high frequency irregular sinusoidal waveform with a higher amplitude towards its middle. If there is no waveform coming out of the knock sensor its best to replace it because it will lead to a rise in fuel consumption and the engine management system may reverts to emergency knock control and reduce overall engine performance.