EPC

ELECTRONIC POWER CONTROL

EPC LIGHT

The EPC fault indicator lamp is very well known among the VAG community, and for those not yet familiar with the EPC light;   it's an  amber symbol in the instrument panel displaying the uppercase letters EPC, which is the abbreviation for Electronic Power Control. This EPC lamp is often referred to by automotive technicians as K132.  EPC is synonymous to Drive-by-Wire which means that the vehicle concerned is fitted with an electrically controlled throttle valve. Restated, the old mechanical throttle cable has now been replaced by an electronic throttle control system. Vag vehicles fitted with  Motronic Engine Management version 5.9 ECUs  and older, still use a cable operated throttle interfaced with  a Throttle Control Module (TCM) and appear to be less susceptible to EPC related problems but not immune. Whereas vag vehicles fitted with Motronic Engine Management version 7.5 coupled to a Drive-by-Wire system appear to be somewhat more susceptible to EPC related problems. This is because ECUs with MEM 7.5  was specifically designed to handle the new torque-oriented  EPC function.   

However, the  bright orange EPC fault indicator light has absolutely no effect on the functionality of the Throttle Control System as a whole. When the ignition is initially turned on, it is perfectly normal for the EPC light to come on briefly,  then switch off again, if and only if it detects no Throttle Control System DTCs in memory and also determines that the TCS is working OK.  This ECU self diagnostic test takes all of 3 seconds. But, should a problem exist, the EPC light will remain on, since it needs to inform you of a DTC stored in memory  and that any additional TCS faults won't make it glow any brighter. (NB! There is no other visual way of showing you that there are several EPC errors other than with a scan tool). 

DRIVE-BY-WIRE

The Drive-by-Wire system consists of  an accelerator pedal module, that houses  two accelerator position senders, a throttle control module that also housing two position sensors,  a throttle
valve drive servo motor, an EPC light,  an ECU and of course the wiring to connect them together. 

THROTTLE CONTROL

The two accelerator position senders are a fixed part of the accelerator pedal and in reality are potentiometers. They get their supply voltage from the ECU that is capable of component diagnostics and constantly monitors its inputs. When the ECU detects that one potentiometer signal failed, it sends a DTC to the memory and turns on the EPC light then switches to the second potentiometer. It uses the accelerator pedal input voltage and translates its position  into an output voltage that drives the throttle body servo motor that controls the butterfly valve. The two throttle two position sensors, sends feedback to the ECU. Once again theses sensors are potentiometers, also monitored by the ECU and as above, if one potentiometer fails it sends a DTC to memory, turns on the EPC light then switches to the other potentiometer, but not necessarily in that order.

WIRING

The CAN Bus wire pair for the Powertrain  are Orange/Black and Orange/ Brown but there is also a supply wire (Red) and an earth (Black) wire, to each of the Drive-by-Wire components. Each of these wires have a plug and each of these plugs have at least four wires. Do the math and you could have 8 plugs - 32 male contacts pluging into 32 female contacts. The accelerator pedal potentiometers fault finding procedure.  Any of these contacts could be intermittent, all of which will cause the  EPC warning light to light up and if any of the Drive-by-Wire components fail will do the same. Considering cars drive on bumpy roads, withstand extremes engine heat and freezing temperatures at night besides rainwater that could find its way into the wiring harness. All of which could contribute to intermittent electrical connections.

REPAIRING EPC FAULTS

Repairing EPC faults are easy but needs to be systematic, because everything that can cause the problem needs to be thoroughly investigates and exonerated before the next item is suspect. Before any major or expensive components are replaced, check the wiring. Check the wiring, Check the Wiring.  Suspect the potentiometers first since they suffer from wear and tear. 

POTENTIOMETERS

A potentiometer is essentially a potential divider. Restated, its a three legged device, with a fixed high potential (voltage) and a fixed low potential (voltage)  at two of its legs. The third leg outputs a variable potential (voltage) less than the higher potential and more than the lower potential.  A potentiometer is normally made of bakelite or fibreglass with a carbon track attached to it.  The variable output makes contact with slider that runs on this carbon track. This sider/carbon contact isn't very good because its a sprung loader pressure contact. Besides when the carbon track wears through which is just a matter of time because it is constantly at work when you accelerate. It is going to give you the EPC fault guaranteed.

Feel free to upload your VW, SKODA, SEAT & AUDI scans.

EPC NIGHTMARE

EPC WARNING LIGHT

Over the past 3 years I have had some  13775 EPC information requests. That's roughly 4500 request per year, each and everyone of  them EPC related.  I manages to help several Vag car owners with their EPC problems however many were unable to give me the  DTC codes that could be causing the EPC problems. So, If you have a scan of your car feel free to upload it to my blog, I will analyse it and post the answer for everyones benefit.  I have found that the commonest EPC problem is the accelerator pedal potentiometers. However they cannot be purchased as a separate item. You have to buy the complete accelerator pedal. There is a plug that is attached to  the accelerator pedal, the plastic bit where the yellow stickers are, contains the pots.  If you are having EPC problems you are not alone. Read some of your fellow Vag car owners woes.

NO EPC DTC CODES

What is EPC on a Volkswagen? My car loses power all the time. If  I turn the car off and leave it for a while,  the problem goes away. This happened to be a couple of months ago, and  I was forced to take  it to a VW dealer.  They had no idea what to do. The car idles  really badly and the EPC light is on from the moment I start it,  besides now the check engine light is also on. I'm  thinking about replacing the throttle body but it cost about is $600. That's crazy man.

TOO VAGUE & NO EPC DTC CODES

My EPC light came on and car lost all power, so now I am having the most weirdest problems. I got stuck on the freeway, my EPC light came on and I had to pull onto the shoulder of the road because I lost acceleration. Disconnected and reconnected the negative battery terminal to reset the system, then she was driving fine. Took it to VW guy but he has no idea what an EPC problem is or at least he wanted me to  pay him  first before would help. He wants $85 an hour.

NO EPC DTC CODES, CAN'T ASSIST

I have an  VW Polo 1.4 and the 'Check Engine light' and EPC warning light  blinks for the past few months. Replaced the throttle body and potentiometer  and wiring to the engine manifold were replaced.  The same problem still persists and car  will stall at random causing these warning lights and EPC to switch on.

NO EPC DTC CODES, NO HELP

My polo 1.2  epc light comes on when I stop at traffic lights and goes into limp mode then can only drive  15 mph max without   pressing the accelerator. Took  it to a service agents who condemned  the throttle body, so had it replaced. The EPC light still comes on.

Feel free to upload your VW, SKODA, SEAT & AUDI scans.

WHY ENGINE LIGHT COMES ON

EPC LIGHT

Seeing a VW or a Volkswagen or Polo da Volkswagen or a VAG car or a new Polo on tow,  is becoming an all too familiar site, - view picture below. VW cars are seen piggy-backed and carried to service centers on a daily bases because VW owners are encountering serious trouble with their Volkswagen cars.  

Many Volkswagen drivers are often stranded on the high ways or freeways whilst driving to and from work because their VAG cars are throwing tantrums, by going into limp mode and turning on the EPC light.  Most VW drivers have no idea why engine light comes on. 

I've been late for  meetings on several occasions because of this. On a few others, I couldn't make it to the  bank in time because the Electronic Power Control -EPC- circuit incapacitated my VW Polo Classic 2.0L Highline. The worst was when I took my daughter to the dialysis clinic and the Electronic Power Control (EPC) light came on, because I ran over a speed bump a little too fast. This resulting in "Limp Mode" causing my daughter to be substantially late for her dialysis session. This could have been a life or death situation but fortunately it wasn't.

I took this photo with my cell phone. The picture quality really isn't good, so therefore the
Bluemotion badge to the left of the right side tail light  isn't clear at all.  But I couldn't pass-up
the opportunity to capture a VW Bluemotion 2012 loaded on a roll-back.

Anyway,  lets look at why this very risky and inconvenient issue haunts most VAG car owners. All Drive-by-Wire cars (since 2000) has an Electronic Power Control (EPC) light. The EPC dashboard warning lights are not exclusive to VW or VAG cars but affects most other new cars regardless of its manufacturer though the common denominator is Drive-by-Wire and an Engine Control Unit (ECU) often called the Powertrain Control Module (PCM) with an embedded microcontroller supplied by the same manufacturer.  EPC stands for Electronic Power Control which is controlled by the ECU (Engine Control Unit). In essence the Engine Control Unit (ECU) is a microcontroller with associated circuitry which control the sub-modules in the car, all connected together by either OBD II or CAN-Bus. Certain outputs from these sub-modules can activate the Electronic Power Control  circuit, especially if the reason for sending its signals to the ECU (Engine Control Unit)  could cause damage to the engine or is a danger to the passengers. For example, if the car runs out of oil, or if the emissions exceed the prescribed level, or  if  the car hits a speed bump a little to hard or if a brake bulb fails.

In the first case the oil level sensor will detect that the lack of oil in the crankcase and since there is a possibility the engine may seize-up, it sends a pulse train to the PCM to activate the Electronic Power Control (EPC), which cuts the power to the engine, making the car go into "Limp Mode" and switching on the EPC warning light. In the second case the lambda sensors on either side of the catalytic converter  will detect the fuel rich exhaust fumes and send a pulse train to the PCM to activate the Electronic Power Control (EPC), which cuts the power to the engine making the car go into "Limp Mode", thereby limiting carbon pollution and  and switch on the EPC indicator light (epc warning light) . In the third case the engine knock sensors will detect the suspension knock as the car hits the speed bump and will send a pulse train to the PCM to activate the Electronic Power Control (EPC), which cuts the power to the engine making the car go into "Limp Mode" and switch on the EPC dashboard light. In the fourth case, one of the Electronic Control Unit or Body Control Modules (BCM) sensor will sense that a brake light is open-circuit, send a pulse train to the PCM to activate the Electronic Power Control (EPC), which cuts the power to the engine  making the car go into "Limp Mode" because in that condition the car is not roadworthy. The EPC dashboard light is a very graphic demonstration that there is something amiss in you VAG that needs to be remedied.

There are several other sensors strewn throughout the car and many of them can have an effect on the Engine Control Unit (ECU) and cause the EPC light to come on. Sometimes when the EPC fault light comes on, it may be a spurious error, based on past driving cycles. A driving cycle is calculated from the time the engine starts and drives -which should be a min 5 minutes- until the engine is switched off. It could  take three drive cycles to clear a spurious error but if the fault persists it has to be diagnosed on a VAG-COM diagnostic tester.

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Here are some Non  Volkswagen Websites I highly recommend,  

http://electroniques.blogspot.com

http://photojani.blogspot.com

http://expowp.blogspot.com  

VW ELECTRONIC POWER

EPC LIGHT EXPLAINED

As I mentioned before in my older blogs, the new generation of VW cars are designed to turn on an EPC Light (not check engine light) so that only the  Volkswagen dealership service technician or technicians are supposed to do any an all servicing and repairs.  The VW workshop manuals specifically discourages anyone other than a qualified or trained mechanics / auto-electrician and automotive technician to perform servicing, especially changing codes and performing readiness test.  This is because  incorrectly set readiness and adaptation settings can completely disable your car and virtually render it useless. To repair it would then cost a small fortune.

CHECK ENGINE LIGHT

An earlier blog, covers some late model VAG cars with fuel injection and electronically controlled throttle body instead of the traditional accelerator cable controlling the throttle valve. It is called Drive-by-wire or DBW for short. When the Engine Control Unit -ECU, which invariable is a computer in its own right detects a fault  Diagnostic Trouble Code - DTC  in the Drive-by-wire system, it registers a fault Diagnostic Trouble Code - DTC in its non volatile memory and turns on the EPC light, disables the accelerator and throttle body, limit the engine to a maximum of 1500 rpm -"Limp Mode".  This would be sufficient power to "Limp Mode" the car to a service centre without causing further damage to the car or unduly polluting the air should the fault cause it to smoke. This is a safety precaution and can be equated with, what would happen if  an accelerator cable got stuck in the downward position. Disaster could follow. The Engine Control Unit -ECU collects faults Diagnostic Trouble Code - DTC from all senders and stores an internal list, which is only visible with a diagnostic tester. Diagnostic Trouble Code - DTC can range from excessive emissions to - intermittent air bag connections, from brake light failure to - depleted brake pads, from interior ultrasonic failure to - immobilizer problems to even disconnecting the battery. Each of these faults generates codes, some of which can be viewed in future blogs.

Should the Volkswagen Engine Control Unit -ECU  considered a Diagnostic Trouble Code - DTC to be so serious that it could possibly do harm to the engine or the environment, it will inhibit the throttle function and limit the engine revs or even disable starting or idling completely.  Unfortunately the only way to repair such problems, is to connect the  Volkswagen Golf,  Jetta, VW Polo, or Volkswagen Beetle, to a dignostic tester through its CAN-Bus / OBD2 / OBDII port and view  Diagnostic Trouble Code - DTC  if any and  Diagnostic Trouble Codes, clear them from memory and perform corrective procedures.  Below is an overview of the Electronic Power Control Circuit - EPC and how the Drive-by-wire system operates.

The basic operation of  the Electronic Power Control (EPC) Schematic showing inputs
from drive-train sensors and output signals to drive-train actuators.

Other INput senders could result in similar problems. For example - the Oxygen Sensor could detect that the exhaust fumes carbon mixture exceeds the prescribed level which is toxic to  the atmosphere and the environment. It could disable driving of the vehicle by enabling the Electronic Power Control Circuit - (EPC), turning on the EPC warning light or even disable starting not allowing the car to idle. This could be due to a dead plug causing the idling to be erratic and not burning up all the fuel. This un-burnt fuel will invariably change the exhaust fumes composition which triggered the Catalytic Converter and Oxygen Sensor in the first place.

Like wise, when the brake light bulbs blow or the fuse to the brake circuit blows, an INput signal from the brake light sender could also activate the Electronic Power Control Circuit - (EPC), turning on the EPC warning light causing the car to go into "Limp Mode" because driving a car on a public road without brake lights is an accident just waiting to happen. In fact the Engine Control Unit (ECU) looks upon this car as non-roadworthy as a safety procedure. In a previous blog I described an Electronic Power Control Circuit - (EPC), which switches on the EPC light problem caused by an INput  signal from one of the knock sensors with the same results as above. Other senders INputs that can cause similar problems are:-

The Engine Speed Sender G28 situated at the flywheel.
The Hall Sender G40 situated at camshaft pulley
The Hot Air Mass Meter G70 and intake Air Temperature sender G42 situated near intake manifold.
The Lambda probe G130 situated upstream of catalytic converter
The Lambda probe G39  before catalyst converter
The Knock sensor I - G61 below intake manifold
The Knock sensor II - G66 below intake manifold
The Accelerator Position Senders G79 and G185 embedded in accelerator pedal (EPC Problem)
The Clutch pedal switch F36 situated in the drivers foot well.
The Brake light switch F and brake light switch F47 situated in the drivers foot well.
The Throttle control valve / motor drive assembly  J338 
The Angle Senders  G187 and G188 situated inside throttle body.
The Fuel Pressure Sender -G247

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POWER CONTROL

ELECTRONIC POWER CONTROL EXPLAINED

As I mentioned in a previous, blog German Automotive Technology is really, really cool. German car design and automotive technology is currently at the forefront of going green, with the result that all other motor manufacturers are turning green with envy. Pardon the pun. German car design technology doesn't flaunt the colour green as eco-friendly but rather blue. 

Mercedes is pushing Blue Efficiency as their future technology and VW is flaunting Bluemotion as their new technology.  Polo de Volkswagen Bluemotion technology started out with the 2007 Polo (not my 2007 Polo Classic) and may be seen in some of their new vehicles. It's futuristic in the sense that it saves fuel. It saves all the fuel that would have been used, if the car was allowed to idle. Blue Efficiency and Bluemotion fuel technology doesn't allow the car's engine to idle, so when you start the car, it doesn't actually idle but the dashboard lights indicate that the engine has started. Logically there is no engine noise since there are no revs. The moment the car is engaged into gear and you remove your foot from the brake pedal, the engine starts instantly and pulls away as if it has been idling all the time. Exactly the same happens when coming to a compete stop at a traffic light or stop street. The engine switches off when the car comes to a halt, and remains off whiles you foot keeps the brake pedal depressed. However, the moment the pedal is released, the engine starts and the car moves off as if the engine was never switched off. There is no delay.

Having  said that, can you contemplate or just imagine the complexity of the electronics, both hardware and software employed in Bluemotion Technology, considering that many of the service agents are even stymied by the current German technology used in cars prior to 2008. The EPC on Volkswagen, Audi, Skoda, is just one of them. Central locking is another, ABS is a third and airbag a fourth. Intermittent reverse light whilst driving a fifth, brake light is on, blowing brake light fuses is a sixth and the list goes on. The repair and service charges for the non-Blue motion vehicles are already over the top so what can we expect to pay for repairs to Bluemotion technology vehicles. Besides who is going to repair them? Currently service agents are trowing spare parts at each electronic problem hoping that it would solve the problem but in most cases doesn't solve the problem.

Anyway, it appears that quite a few visitors who viewed my Electronic Power Control - EPC solution blog have no idea what a potentiometer (sender)  is, so let me explain and use the VW Polo accelerator pedal [accelerator position sensor (G79 & G185)] as a basis for understanding. Below is a picture of a potentiometer marked "A" that may be used in an electronic circuit. It specific one could be used as a volume control in an amplifier, or a sensitivity control on a disco strobe or a brightness control for a lamp dimmer. The uses for potentiometers are endless and has been used in cars for quite some time.

An overview of the  Electronic Power Control Circuit - EPC  in Volkswagen, Audi, Skoda.

The accelerator sender marked B and the throttle body housing marked C as seen above each have a gang potentiometer (meaning more than one potemtiometer in the same housing)  VW calls these both these potentiometers senders since they provide input to the ECU - Engine control Unit.  The ECU controls  the Drive-by-wire and any problems with it causes the car to go into "Limp Mode" resulting in the EPC warning light or other dashboard lights to come  on. Have a look at Electronic Power as to how the entire accelerator throttle  circuit is controlled and interfaces with the OBD2 /OBD II and Can Bus network.

MANIFOLD

MANIFOLD / EXHAUST

It was about 2:30 a.m. when I returned from a long distance trip. I was tired but smiled to myself before I climbed into bed because my 2007 VW Polo Classic Highline really performed well and brought me home without incident. I was amazed, blown away in fact. 

After breakfast the following morning, I intended to go to Milnerton to see a client but when I started the VW Polo, I was greeted by  frighteningly loud noise. I smiled too soon. Immediately I switched off the engine. It actually sounded like the VW Polo had no manifold system fitted at all. For the record it wasn't like the sound of a broken silencer or a hole in the exhaust system. It literally sounded as if there wasn't any exhaust system at all.

My first thought was that someone must have liberated my exhaust system during the night whist I was asleep and sold it off as scrap metal. Theft in my locality has become quite rife and this is known to have happened. Radiators and batteries seem to be targeted more often.  However, on closer inspection I was relieved that the exhaust was still there. I started the VW Polo once more rolled underneath the front suspension and discovered hot air was blowing from a space  where the flange gasket is located. It was very awkward to get my hand in there and I was wondering what this repair was going to cost. A trip to "Mister Silencer" and three hundred and twenty bucks later the VW Polo was once again ready for the road. I expected one of the dashboard EPC warning lights to light-up or one of the CanBus interconnected computer modules to immobilize the car but its seems that the manifold exhaust  just runs much too hot to attach a sensor to it.

Anyway, in order to fix or fit a new flange gasket the complete knuckle had to be removed. They hoisted the car on a maintenance lift and inspected its underside for the origin of the noise. It came from above the flexible bend which looked like matted wire mesh. Essentially the joint between the manifold branch and the exhaust manifold had to be removed.  I was told the flexible mesh compensate for vibration, should the silencer knock against a pavement of something, it wouldn't brake off of get damaged because of its flexibility.

Just two days prior to this, a young women ran into my rear bumper with her sparkling new look Audi A8 whilst she was chatting on her cellphone. There was no physical damage to neither of the cars but thought that she was the cause that my exhaust had given trouble. According to the dude at "Mister Silencer", its highly unlikely because the impact from behind would not have pushed the exhaust towards the engine because of its flexibility. Oh well,  either way I had to pay for it. FYI my VW Polo had every service on time since new and currently has 88250 Km on the clock. Soon it will be going for its 90000 km service and my timing belt will be changed. I've been driving with the dreaded fear that it might snap in mid travel and bend all my valves in the process or even bust the tops of one or two pistons.

In my first blog I mentioned I simply love German engineering because when a German designed car snaps a timing belt, there is no mechanical damage to the engine. This is so unlike the Japanese, American, English and French designed cars, all of which bend valves, bend conrods, break pistons or knock holes through their cylinder block. Since my VW Polo Classic 2.0L Highline is soooo different from all the previous German cars I owned, I just have this feeling it was designed along the same money making monopolistic ideology of modern car design - the cash cow that  sells spare parts.

Dudes and Dudettes, if you found this blog informative or even remotely helpful, recommend it to others by clicking on g+1 below.