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". 

VW electric fuel pump

VW electric fuel pump 

VW electric fuel pumps are troublesome and VW, Audi, Seat and Skoda cars are notorious for fuel pump problems. Fuel pump problems commonly affect the Volkswagen Polo Classic 6n, the VW Polo 9N, the VW Bora, the VW Passat, the VW Sharan, the VW Caddy, the VW Golf, the Volkswagen Touareg  and the  VW Beetle, among several other. Its effects can range from intermittent no starting to stalling whilst driving, though most clients would complaint that the car jerks and stall and then just shuts off. However it's not always the fuel pump that's to blame. 

VW fuel pump relay

The VW fuel pump relay is another culprit that goes faulty or rather its external contact terminals tend to burn. So if your car wont start, give the Fuel Pump Relay #409 (1J0 906 383 C) or #410 (6N0 906 383A) a knock or two with a screwdriver handle and should the car start, then it's most likely a bad contact on one of its 7 spade terminal. Remove the relay and see if any of its terminal pins have burnt brown. If not, the relay's internal contacts are probably faulty and needs to be replaced. One consolation is that the relay is fairly cheap and it can be bought on-line at ebay.com for as little as $15. However, a VW fuel pump price on the other hand, is ridiculously priced especially  considering I've had a clients who had to have two fuel pumps replaced in under 9000 km. I don't think they are quality pumps.

When our VW Caddy's fuel pump started to give-in, it presented itself as an occasional engine misfire when pulling away from a stop street or traffic lights. The engine misfire became progressively worse over time, so it was booked-in for a service, for spark plug replacement, oil drain and oil  filter replacement, etc.  At this time we didn't know that the engine misfire was caused by the fuel pump. The day the Caddy was returned, it drove fine for the first two hours then started to misfire as it did before, but thereafter the fuel pump started sounding like a hoover vacuum cleaner. 

I knew it was the fuel pump because I've heard this sound before on both a Polo 1.4 Trendline and a Jetta 1.8 which at the time turned out to be the fuel pump. Anyway, the noise from the fuel pump was really high pitched and annoying, After several hours of driving it became unbearable so the Caddy went back to the mechanic who then diagnosed the fuel pump as faulty. After the fuel pump was replaced the noise disappeared and the miss was gone as well. My friend also  encountered the "hoover vacuum cleaner" with his Caddy but after a few days it just disappeared, so now he occasionally experiences starting problems.

VW  Fuel Pump Relay 409 / 410

VW  Fuel Pump Relay Part # 1J0906383B (409) is a 12V 40A relay with 7 spade terminal connectors, 2 Wide, 2 Standard and 3 mini. The same relay is  installed in VW Polo Mk3, VW Jetta, VW Golf Mk4, VW bora,VW beetle, Audi A3, Audi  TT, Seat Leon,  Skoda Octavia,  VW Sharan and VW Passat, etc.


VW  Fuel Pump Relay Part # 6N0906383A (410) is installed in VW Polo 6N, VW Golf Mk4, VW Lupo 6X, Skoda Fabia 6Y, VW Sharan 7M, AUDI A2, SEAT Arosa, SEAT Alhambra, VW Golf GTI, VW Passat and VW Polo Mk3, etc.

Replacing a fuel pump

Remember that the VW electric fuel pump relies on fuel passing through it for both cooling and lubrication. If or when running the fuel pump dry, fuel starvation can accelerate  internal component wear and may cause  the fuel pump motor to overheat and burn out. Electric fuel pumps run from the moment the ignition is switched on, so its fairly obvious that after a few years of operation their armature bushings, gears, commutator and brushes will suffer wear and tear, causing a gradual loss of pressure. Loss of fuel pump pressure commonly causes the "EPC" light to come on. A fuel leak or an Evaporative Emission System (EVAP) leak would also turn on the "EPC" light as well as the "Check Engine" light because the low inlet manifold pressure would upset the engine's air-fuel ratio and degrade engine performance and reduce fuel efficiency.  It would also diminish  power and acceleration, and possibly even cause stalling.  So if you need to replace your VW electric fuel pump, make absolutely sure you depressurize the fuel system before disconnecting the fuel lines. The easiest way to do this is to remove the fuel cap, remove the electric fuel pump fuse or relay and crank the engine a few times. 

Faulty Fuel Pump Flanges

There is currently a VW / Audi fuel pump recall, though its not necessarily the pump that's defective but rather faulty flanges manufactured by German supplier Continental Automotive GmbH. Apparently they've been supplying VW, Audi and Porsche with flanges that seem to crack and cause fuel leaks and potential fires. Apparently Continental sold the potentially faulty flanges to eleven automobile manufacturers and five OEM parts supply companies. Audi, Ford,  Fiat Chrysler, General Motors,  Jaguar-Land Rover, Lamborghini, Mercedes-Benz, McLaren, Porsche, Volvo and VW are just some of the automakers who used these industry-standard polymer flanges but other automakers may possibly also be at risk. 

Meanwhile Volkswagen, Porsche and Audi already recalled nearly a half-million vehicles because of leaky flanges, that cover fuel tank openings and is used for the fuel pump and other items. U.S. safety regulators are currently trying to track down gas tank flanges that may crack and cause fuel leaks on what could be millions of cars of all makes and models.

Continental Automotive GmbH supplied millions of fuel pump flanges to 11 car makers that can cause a potential fire. Is you car one of them?

— Faried (@Syba_seca) July 10, 2017

Electronic Power Control

Electronic Power Control

What Does the Electronic Power Control (EPC) Warning Light Mean?

Traditionally hand brake, accelerator pedal, clutch and bonnet release, used some sort of cable system and the steering column and gear levers used several mechanical linkages. Today virtually all these mechanical systems have been replaced by electronics in the form of sensors, feeding computers and electric motors performing as actuators. The legacy accelerator cable that controlled the throttle valve and fuel supply in the trusty old carbureter has been entirely replaced by electronics. It is now referred to as drive-by-wire (drive the car by means of electric wire control) and the EPC circuit oversees drive-by-wire system.

So what is an EPC circuit?

EPC stands for Electronic Power Control (EPC) and is a sub circuit of the car's computerized engine management system better know as its ECU which stands for Electronic Control Unit or  Engine control Unit. The EPC circuit uses the input signal supplied by the accelerator position senders and  the throttle angle senders to calculates how much engine power the driver requires. The EPC system also receives input signals from other systems on the car, like the stability and cruise control systems and translates this data into engine torque by means of the actuators.

The EPC circuit also monitors these components at start up and whilst driving and should it detect any malfunction, it will readily illuminate the EPC warning light . The EPC light is a bright yellow/amber instrument cluster light displaying the letters EPC. But it's just a 'Indicator Symbol light' that  informs the driver that an issue occurred in the torque system. Some faults within the EPC circuit will more than likely disable other functions on your vehicle that may even cause it to go into limp mode and not rev or perform very sluggishly.

EPC Warning Light

Since the EPC is a sub circuit of the ECU which supervisors several other systems on the vehicle, it is likely that other warning lights my also illuminate  on the instrument cluster. For example the Check Engine Light (CEL) may illuminate to indicate that the engine itself isn’t operating at normal efficiency. At the same time the stability and cruise control will be disabled and their respective lights may turn on as well.  

When this happens, you will need to have your car scanned for diagnostic trouble codes (DTC) or you could do it yourself if you have an appropriate scanner. Once the error codes are identified, it would be relatively easy to repair / replace the component responsible, and thereafter clear the fault codes. The illuminated lights should all turn off and the car should once again drive as per normal.

Is it safe to drive with the EPC light on?

Many people inquire  whether or not it safe to drive with the EPC light on? In my humble opinion, I would say,  Yes it is safe to drive with the EPC light on, because the EPC light is an abler light and not a red light. Red lights dictates that you shouldn't  drive the car at all, until the problem causing the red light to illuminate is repaired. Whereas an amber light is just an information sign. One can equate dashboard lights to road signs, for example if a red traffic light or a red stop sign with white-background  or other red and white regulatory sign is blatantly disobeyed, it will more likely than not result in harm or injury. Round red and triangular red road signs are warning signs and means danger. Also any sign with a white background signifies the sign is permanent  whereas a sign with a yellow background signifies that the sign is temporary and any square /diamond shaped orange/amber signs are used for roadway works information and guidance.

So return to the subject at hand, yellow/amber lights are therefore informative and temporary. However when the EPC light is on and the car goes into limp mode then its not safe to drive with the EPC light on, because you will be going dead slow and be an obstruction to other motorists. Limp mode is just a shortened form for limp home mode which is  an operating mode set by the vehicle's on-board  computer which is pre-programmed by the manufacturer. This program limits  your vehicle throttle in order to protect the engine or the car itself or its occupants from harm or injury and the car should only be driven to take it for  repairs.

As can be seen, the four signs on the right are red with the top two including white
whereas the four signs on the left are all yellow  which is informative and temporary. 

However the severity of the EPC problem can vary greatly and the vehicle may not be operable at all.  Common cause of  car’s EPC circuit malfunctioning are its sensors. Replacement normally solves the problem, however EPC faults can register intermittently to the point of frustration. In such cases it's very likely the wiring harness are intermittently faulty especially where the plugs connect to the sensors. If your engine suddenly shuts off while driving, you may want to look at the Engine speed sensor. The  crank shaft rotation sensor also commonly fail, when starting the car's engine while stationary. A tell tale sin is that the  the engine switches off after two second of idling. 

The brake light switch is yet another  EPC light trigger and is solved by replacement. This switch is a double pole double trow switch and isn't physically associated with the brake other than the same switch is used. On automatic vehicles brake switch failure locks the gear lever in Park and prevents  from selecting any other gear. The Mass air flow sensor is another common cause of EPC problems but in many cases it's not the MAF itself. It may be due to minor cracks in the rubber hoses that causes air to be sucked in, upsetting ECU calculations. The Throttle body and its angle sensors and drive motor is another is also another EPC problem child.

@volkswagenindia why am I getting EPC light again and again. Already 7 times repaired. Tired!! @Volkswagen pic.twitter.com/S1GzM6shNT

— विरल (@Viral_HS1) July 1, 2017

My EPC light

My EPC light

If you've had your VW, Audi, SKODA or SEAT for a while, you're probably familiar with the EPC light and already experienced its wrath. If you haven't encountered the EPC warning light as yet, then you are definitely one of the lucky ones, because I know of several VW Polo, Seat Ibiza,  VW Jetta, VW CC, Passat, Audi A3, Audi A6, Seat Leon and even Porsche owners with odometer readings as low as 1500 Kilometers, who got spooked by the EPC light when it first stuck. This EPC light is known to trigger instant panic and fear in many VAG car owner, and I don't blame them, since it can be a scary and dangerous experience, especially when the car goes into limp mode when you're overtaking or the engine just dies when exiting a freeway  off-ramp or when entering a highway on-ramp during peak hour traffic.  

Electronic Power Control

However, if you have no idea what an EPC light or an EPC fault is, nor why this warning light turns on, then you should do yourself a solid and continue reading. In a nutshell, the EPC warning light is a standard feature in all ODB-II compliant models of Volkswagen, SEAT, SKODA and Audi vehicles. Most of them, are fitted with 'drive-by-wire' technology, though neither are exclusive to VAG cars. And when I say VAG cars, I also mean  Porsche, Bentley, Bugatti, Lamborghini and Ducati. Toyota, Honda, Ford, Mercedes also has it, in fact, virtually all cars manufactured post 1996  have an EPC warning light. EPC is an acronym for Electronic Power Control, and its a  warning light that resides inside the instrument cluster display.

EPC Light

Nonetheless, the EPC light is not all doom and gloom. It is there for a reason, and that reason is to safeguard the car and the engine from damage or destruction, especially considering what they cost to repair these days, let alone the cost to have an engine overhauled. Many people are under the misapprehension that the EPC light indicates an issue  with the cars  computerized system, whereas mechanics tend to echo that the EPC light indicates  a potential engine malfunction, though that's not strictly true either.  

MIL 

Before we continue, I just needed to add that when the engine malfunctions, it illuminates the Malfunction Indicator Lamp (MIL) aka Check engine light (CEL), which is indicative of  a computerized engine-management system malfunction. It even has an amber/orange icon of an engine, so as to draw your attention to the engine. Furthermore if this amber icon engine light is steadily illuminated, it indicates a minor engine fault but when it blinks it signifies a major engine fault. On the other hand, the EPC (Electronic Power Control) warning light  is a distinctly separate light from the MIL or CEL because it is related to a different function.

The more appropriate answer to 'What is an EPC light?' would be that the Electronic Power Control warning light, indicates a malfunction in your VW, Audi, SKODA or SEAT's  throttle control system, though once again that's also not totally accurate either.  So let me throw so light on the subject. The EPC light is in fact a diagnostic test light. So when the car's ignition is first switched on, the EPC light is illuminated for about three seconds. If there are no faults in the EPC system the light will automatically extinguish.

Drive by Wire

This three second time period is the duration of a self-diagnostic test. Effectively the Motronic ECM (J220) checks for malfunctions  in the Electronic Power Control (Torque system) accelerator system (drive-by-wire system), which includes the Throttle Body Drive Stepless Motor (G186) with its dual   independent Throttle Drive Angle Potentiometers (G187 & G188), the Accelerator Pedal Module with its dual independent Throttle Position Sensing Potentiometers (G79 &G185), the wiring harnesses that connects them all together and its associated sensor inputs from the Cruise Control  System, the Anti-lock Brake System (ABS), the Oxygen Sensor Control, the Automatic Transmission and the Air Conditioning System, etc. 

Charge Air Path

Here Air conditioning system mean all components involved in conditioning the air in the inlet manifold prior to combustion, implying the Throttle body / Mass Air Flow (MAF) sensor G70 and not A/C as in HVAC.  That being said, the functionality of an Electronic Throttle Control (drive-by-wire system) can regulate the Charge Air Path far more accurately than a physical cable between the accelerator pedal and the throttle valve. 

NonVolatile Memory

This being the case, by the time the EPC light illuminates on the dashboard  in response to some sensor detecting a problem  whilst driving, the problem already occurred.  The  EPC warning is just a way to tell you that there  was a glitch in the EPC (drive by wire system) and generally remains lit until the fault is cleared. The EPC light is known as K132 and is turned on by the Motronic ECM by providing the Ground  connection that keeps the light burning. At the same time, a DTC is registered and stored in non-volatile memory for later inspection.

Limp Mode

So the key piece of equipment to solving any EPC problem or issue is a diagnostic scanner. The fault below shows that the brake light switch F was the culprit that caused the EPC fault. Bearing in mind, that the Cruise control get its cancellation signal from the brake light when the brake pedal is depressed. When a brake light is fused or the dual contact brake switch goes open circuit and can't provide the requisite signal, the cruise control cannot be cancelled. The ECM detects this condition and construes it as a safety issue and sends the car into limp mode. 

Fault Codes

Essentially the EPC circuit prevented an accident from happening. Implying the brakes would work but the engine would still run at high rev set by the cruise control, meaning the brakes would be ineffective to bring the car to a stop. For safety reasons the EPC system closes the throttle valve to a predetermined position the brake pedal and the accelerator pedal are depressed simultaneously. However if the ECU detects that the brake was depressed before the accelerator, then acceleration will be carried out. 

1 Fault Found:
16955 - Brake Switch (F) 
P0571 - 35-10 - Implausible Signal - Intermittent

The fault below shows  that there is  an electrical malfunction in the Drive by Wire  circuit causing the EPC light to illuminate. After clearing the fault code, the EPC light just comes back on. The ECU was suspected and replaced but didn't solved the problem. It turned out that the  wiring harness between the ECU and the instrument cluster.

1 Fault Found:
18084 - EPC Warning Lamp (K132) Circuit: Electrical Malfunction 
P1676 - 35-00 - - 

The fault below  was on an Audi where signal from the Transmission  Control Module (TCM)  to the ECU was intermittent causing her to go into limp mode and idle really rough. Turned out that the TCM got wet from rain water that leaked into the carpets.  

1 Fault Found:
18265 - Load Signal: Error Message from ECU 
P1857 - 35-10 - - - Intermittent

VW electrical issues

VW Electrial issues

As we all know, Volkswagen, Audi, Seat and Skoda have several mechanical and electronic components in common, among which are their wiring looms with their huge variety of connectors. These connectors range from as few as 1 or 2 contacts per plug, to as many as 16, however the ECU and TCU edge connectors can range anything from for 32 to 68 pins,  up to 80 pins and even beyond. 

AUDI, VW, Skoda and Seat 2 pin connectors P/N535972721 - P/N1J0973772

Most modern cars have numerous control modules, for example the ECM (engine Control Module), the TCM (transmission Control Module), ABS Module (Anti-lock Braking System), Air bag Module, Convenience Module, Steering Control Module, Radio Module, Central  Electronics Module, Instrument module, CAN Gateway Module to mention just a few. Bearing in mind some cars have as many as 40 modules or more on board. 

TCU, ECU and Air bag plugs showing the multiple pin contacts.

Some of these modules control the sound system, the telephone system, the satellite navigation system, xenon ballast module, fan control module, suspension height control system, traction control system among so many others. Each of these modules and systems have numerous connector terminals / pins, some for its primary power, some for standby power, some for data communications, some for sensor inputs, some for actuator output, some for future expansion, some to accommodate different models  and probably some just for show. Each of these modules can have just a few contact terminals / pins whereas others can have close to 100 contact pins.

Molex ECU and TCU interface connectors that are normally
soldered onto the Printed Circuit Boards

When this glut of electrical contact terminals / pins / connectors are compared to those  of a pre-1994 vehicles, you shouldn't be surprised to see that they increased by at least a 100 fold. Meaning if your car of the 90's had as few as 200 electrical connections throughout the entire car, then its 2017 version would have 2000 electrical connections bumper to bumper. This is just a poor estimate for the sake of clarity but in reality their are way more connections. Pessimistically speaking that implies there are an extra 1800 connections that could go awry at any time, especially whilst driving in peak hour traffic or on a deserted road. Some of these 1800 connections include those for the EPC circuit, the throttle body, the check engine light, the crank sensor etc, and some many others that can be the cause that your car breaks down at the road side, leaving you stranded when you need the car most.

Female terminals seem to be the most troublesome of all connectors.

Since all cars are subject a certain amount of vibration that permeates throughout the body of the car, wiring looms and their connections are vibrating along with the engine, or bouncing and shaking along due to poor road surfaces. The car's body also flexes as it drives and the wiring harness flexes right along with it. Most of the VW plastic plugs and connectors have a locking system to keep them together, to prevent them from becoming adrift  whilst driving. But if there is excessive movement in the plug itself that causes contact friction, these contacts are not going to survive very long. The funny thing is, that we see this happening on a daily basis. Then there is chaffing of the loom against the car's body in places where goes through the firewall and the A and post.

The DLC 16 pin connector and a 12 pin connector with their crimp-on terminal pins

Most mornings on my way to work I see at least three rollback tow trucks either in the process of loading a VW or I see the rollback driving in the opposite direction of my travel or I end up over-taking  a rollback with a VW on its back.

So by just looking at the female terminal pins of all the images above, one can clearly see that all of them sport a tweezer like female tension receptacle that squeezes the male pin when it is inserted. Each of these female contact terminals have two little wings that secure them inside its plastic plug but when the terminal  goes intermittent contact it need to be replaced with one of the VW replacement wire kits displayed above.  

VW wiring harness connector terminal removal tool.

The "VW Wiring Harness Connector Terminal Removal Tool" below is used for this purpose, ie to release the terminal pin from its plug. Alternatively you can make your own tool with a paper clip. Straighten the paper clip then hammer both ends flat, then bent it in half to form a staple, so that the two flats are parallel to one another. The hammered flat edges can then be inserted on either side of the terminal pin  so as to push the terminal's wings back onto itself, making it easy to pullout.  Look at the image below. VW 2 pin coolant plug seems to be a favourite that goes wonky and needs replacement. Audi throttle body connector is another. VW, Audi 6 pin accelerator pedal plug is another troublesome connector. But that's best left for another post.

Cross section of terminal plug thats been cut open, see how the two wings in 
the top image is pushed flat by the harness connector tool in the lower image.

Volkswagen Electrical Problems

Volkswagen Electrical Problems

Electrical problems will invariably affect each and every new Volkswagen vehicle on the road today.  Generally, electrical problems are relatively easy to trace and repair, if you know what you doing, but it can be a nightmare when the faults present themselves as intermittent, especially considering cars have now gone CAN Bus, LIN Bus, Byteflight, MOST, Flexray, Zigbee, etc. VW EPC problems tend to be seriously intermittent, making every VW with an EPC issue a real bitch to diagnose.  Of late, more and more VW cars seem to be having EPC trouble among other bizarre electrical problems and very surprisingly, the VW service centers seem unable to repair them. 

Virtually everyone I know who has had an EPC issue, had to take their cars for repairs at least three to four times for exactly the same fault.  There are also numerous VW, SEAT, SKODA and Audi owners, who spent enormous amounts of money on replacement of "EPC issue causing components", yet the EPC faults remain. Essentially they lost money but I normally say they didn't loose money but bought experience and they paid dearly for it. Then there are others who are still waiting on the VW service agents / or some mechanic for their EPC problems to be solved after several months, a year and in some cases even longer.  

There was a time when virtually every electrical issue or loom (wiring harness) problem was associated  with the  FIAT brand. People even ascribed a nomenclature to FIAT - "First In All Troubles". However, it seems like Volkswagen  subsequently bought that patent, and now owns all right to it.

Electrical problems have never been as common place as they are today.

Let me give you an example, the wiring harness between the alternator and  the a  high voltage fuse box mounted on the battery of the VW Beetle has a tendency to melt or it just start to burn. It's a very well known problem and is also really common. It the  main reason that so many Beetles have burnt to a crisp. The Beetle wiring harness running between turn signals / headlights and the ECM is also troublesome -intermittent. The wiring harness resistance between the injector and the ECM changes over time from 1 ohm to above 30 ohms. The wiring harness resistance between the alternator and the battery also increases due to failing fans thus causing excessive current draw resulting in the wiring harness  over heating then melt.

I've seen VW Polo and VW Passt headlight wiring harness melt. The connectors tend to melt due to the type of plastic used and can be traced back to either arcing / overheating of the the bulbs or shorting out of deteriorated wiring. VW Passat coil pack wiring harness also prevents the car from starting and when water enters the wiring harness in the cowl area beneath the windshield,  it caused a short that normally damaged / corrodes the electronic control module. 

Both the Volkswagen CC and the Golf Mk5 GTI now seem to have throttle body wiring harness issues causing the EPC light to switch on and make the car go into limp mode. But there is no fault code that tells you the wiring harness is faulty or intermittent. Another VW CC harness problem to be on the lookout for, is the trunk lid harness that physically breaks over time  due to opening and closing of the trunk. A common problem on VW Pasat is the ignition wires that breaks inside its insulation, resulting in misfires.  VW sells a six pin throttle body sensor connector kit with yellow wires (below) that needs to be spliced onto the wiring harness to circumvent EPC issues when presented with wiring harness / G187 & G188 DTC errors.

Throttle body rewiring kit

Audi throttle body connector kit.  The wires kinda looks like single mode optical fibre cables along with  fusion splice protection sleeves

VW also sells a  six pin accelerator pedal  connector (below) that needs to be replaced as a solution to EPC problems when presented with wiring harness and G79 & G185 DTC errors. There is a likelyhood that this culture of poor quality wiring harnesses has spilled over into all the other VW models as well. To make matters worse, the newest mania among vehicle makers like Honda, Subaru and Toyota  for example,  are to use eco-friendly soy-based insulation wire for their engine wiring harnesses. VW's, Audi and Porsche, uses a soy based wire sheath to encase the engine harness. 

The six pin throttle pedal connector the goes intermittent causing EPC problems.

As a result, rats and squirrels are attracted by the aroma of the wiring harness and nibbles off the tasty insulation causing the bare wires to short out. Apparently these soy-based wire coverings are totally irresistible to rodents. As proof to this, several VW owners who have had electrical problems with their cars have vacuumed rats nests along with dog food chunk from their engine compartments. Others have removed several hands full of hazel nuts shells from their air filter boxes  that squirrels made their haven.  

Replacement six pin connectors for VW Audi SEAT and SKODA

Be that as it may, modern day car soy based car components are not a first, during World War II, some U.S. states used soybean fiberboard for their license plates, which proved extremely popular among goats that made a feast out of them. All I can say is, that VW service centers are going to make a small killing by replacing wiring harnesses of the millions of VW on the road today. Personally, I think you whole biodegradable "go green thing" , "eco this eco that" is overrated and is  getting out of hand. 

Some time back, some Dummkopf  -Dr. Dieter Zetsche- at Mercedes Benz decided that all Mercedes Benz cars manufactured during 1992 – 1996 should be fitted with biodegradable wiring. This leap toward eco friendliness by Mercedes Benz was well-intended but those wiring harness prematurely disintegrated due to engine heat and caused untold electrical problems. VW should in fact take a lesson out of the Mercedes Benz's annals.

See the cracks and the brittleness of the wire insulation after just a few ears of use

However, there is a DIY remedy for biodegradable, rodent enticing soy flavoured wiring harnesses.  Honda Acura Acura supplies a genuine-OEM rodent-deterrent duct tape, which is treated with capsaicin, - super-spicy red-hot chili pepper compound - that deters rodent.  Wrapping you VW wiring harness before rats discover your car is the way to go. Enough said, so let me return the subject at hand. 

Spicy anti rodent insulation tape,

In the not too distant past, Volkswagen Jetta models manufactured between  January of  2005 and January  of 2006 were sold with a "defective door wiring harnesses". It wasn't that the harness was defectives in the sense of not working but rather the harness was made too short. As a result, thousands of Jetta owners were experiencing similar problems as the harness started to chafe and disintegrate through regular use.

Common experiences included loss of power to the door controls, failure of the power window controls, failure of the power mirror controls, failure of the fuel tank latch release, failure of the boot lid release. Other weird experience included loss of audio to the speakers, a tripped air bag light on dashboard, when locking the door with the key fob remote the radio to turn on, or the key fobs just doesn't work, also having to recharged the battery continually because it runs down overnight. The interior door-open lights wouldn't turn off  and neither would the buzzer, the sunroof opened randomly. The turn signal in the side mirror stopped flashing and neither would the hooter work but would beep at odd times when you least expect it.  The windshield wipers worked occasionally and the car alarm would trigger unexpectedly and repeatedly.

In fact most VW Jetta owners complained about loss of some or all of the controls located on the driver's door.  These  faults weren't confined to the driver's door, because it was purely a matter of time before the the passenger door also developed a short or an open circuit in  one or more of its electrical circuit. The only way to remedy the problem was to replace the  broken harness with a genuine VW replacement which turned out to be some 80 mm longer than those fitted in the Jettas doors.

VW Jetta Front door replacement harness

A class action suit was leveled against Volkswagen alleging that they knew the door wiring harnesses were deliberately  made too short at the time these Jettas were sold. It was further alleged that Volkswagen shortened the harness by 80mm was  so that they could save costs, which  would ultimately lead to premature breaking of the door wiring harnesses boosting replacement harness sales.

However, most other Volkswagens electrical problems can possibly be traced back to a a troublesome ground. Water somehow enters the ground wires, in the cowling below the windscreen traveling inside the wire insulation resulting in corrosion. Always check the ground connections located  under the battery tray, or ground connections underneath the air cleaner box, or located inside the windshield wiper cowling or in the engine compartment, or the ground connections on the steering column or behind instrument cluster.   Covering the ground connections with battery terminal grease should offset the corrosion, if any, Remember poor ground connections, can cause a multitude of problems if it they become loose, can cause anything from cam sensor codes, to instrument cluster problems like erratic speedometer display, to misbehaving fuel gauge, to a dead gear indicator light, to non operational windshield wiper,  to a flickering digital clock , etc. 

Volkswagens that are equipped with air conditioning  are subject to high ambient temperatures which often causes the battery to get drained whenever the radiator fan kicks in at full speed with the ignition shut off.  Under high heat conditions, the gas pressure of the refrigerant can activate the A/C high pressure switch, triggering the high speed radiator fan relay to activate the cooling fan. Volkswagen has subsequently recommended a replacement fan relay switch with other minor modification of the A/C high pressure switch wiring, to solve this problem.

Replacement Radiator fan control switch

Whenever your VW misbehaves and you cannot put your finger on it, the best thing to  do is to investigate every ground lug on every bit of the engine wiring harness that you can get at. Loosen it, cleaned it with a  wire brush and some emery cloth and if needs be replace ground lugs that are corroded and possible even the screw/ nut. Don't forget to retorque the nut to the requisite tension. It may even be beneficial to add a second heavy duty ground strap to decrease resistance if any. Heavy duty welding cable from a welders supply store is far more  tolerant to vibration than your average cheap jumper cable wire. Starting difficulties can often be traced / associated to a poor ground connection. 

Remember when repairing wiring harnesses that soldering is not the recommended nor the appropriate method of repairing  it.  Solder joints are not flexible and tend to break after  while due to vibration.  Always use insulated crimp lugs and bullets like these below on connecting terminals especially at ground distribution points.

Lugs, bullet and spade connectors for repairing ground connections.

There is a tendency among car manufacturers to  miniaturize the physical size of electrical connector contacts and thereby the oversize of the connector. The problem is that the surface area of contact is remarkably reduced and are thus prone to intermittent contact under vibration. This has now become very evident on the wiring loom connectors that interface with the throttle body and the accelerator pedal to the point that they need to be replaced when they go intermittent. Don't bother to spray them with contact spray, just replace them. they are cheap enough to buy rather than suffer constant EPC issues and they are even available on Amazon, ebay, DHgate, and other online auction.

@DomLittlewood I need your help on a case I have with Volkswagen. A Brand new Volkswagen Polo numerous electrical problems & now caught fire

— Deano Luke (@95deanluke) August 30, 2016