Wednesday, January 9, 2013


VW - DRIVE BY WIRE (Drive-by-Wire)

If you arrived on the VW Polo website because you searched for  Drive by Wire (DBW), EPC, or EPC light or engine won't rev, Steer-by-Wire, or limp mode,  then you have certainly arrived at the right place. There are several definitions for ECP, the first of which will be explained, is Electronic Parts Catalog (EPC).

EPC stands for Electronic Parts Catalogue (EPC) and all Audi, Volkswagen,  Skoda and SEAT parts are listed in ETKA V7.2 EPC (Electronic Parts Catalogue). This catalogue is purchasable online and downloadable but the file is huge. Companies like Mercedes Benz, Toyota,  Enigma, Attrakt among many, many others host computer based electronic catalogs of the individual auto parts and accessories that make up their engines, cars, tractors, specialized machinery and farming equipment etc. Restated, an EPC is a catalogue in electronic format much like CVS data or a database file or similar, that can be downloaded or is accessible online.

Then there is the second type of EPC - Electronic Parts Catalog (EPC) software. MultiCat and Msys.EPC are companies that specialize in the software that can display an exploded view of an assembled device. For example, the exploded view of an engine, or gearbox, or cylinder head, showing the individual bolts and nuts, flanges, hoses and brackets, etc. and their component part numbers.

Thirdly, there is also the Electronics Parts Catalog (EPC) which is an electronic list or database of semiconductor components, from diodes to transistors to integrated circuits to thyristors, etc... This EPC is often called and equivalents book or catalog and hosts the specifications of semiconductors from several manufacturers. A typical EPC is the RS Electronic Components and Tools Database. This EPC doubles up as the third type of EPC which is the Electronic Product Code. Component Product Codes look like,  1N4148 or BC337, MCP2515, TYN812RG, etc... for electronic components.

However, there are many more EPC definitions, some of them can be found at the end of this blog. I could explain all of them individually but none has any relevance to the subject at hand, viz EPC - Drive by Wire. Drive-by-Wire also know as  DbW, Steer-by-Wire "x-by-wire" or simply "by-wire".


And finally, the Electronic Power Control (EPC) that freaks out almost each and every VW 1.6 PoloAudi TT, Skoda, SEAT and  Golf TDI, owner. Most vehicles with Drive by Wire [Drive-by-Wire (throttle control)] usually have a Electronic Power Control (EPC) indicator lights on its dashboard which lights up when  there's a problem with the Drive-by-Wire system. This would involve the two accelerator pedal sensors G79 and G185 and in some cases the two sensors G187, G188 inside throttle control valve body - control actuator. [As discussed in my previous blogs] When the engine idles, neither the Throttle Valve Angle Sensor nor the Accelerator Pedal Position Sensor are monitored for faults by the ECU, as suchthe engine does not respond to accelerator input but will limit engine to 1200 RPM.

The  basic components that constitute the Electronic Power Control (EPC) circuit. 
There is no throttle cable involved, because its an electronic throttle control.
The Electronic Power Control (EPC) circuitry consists of EPC light, Accelerator Pedal, Throttle Control Valve,  DBW  (no throttle cable,) Injectors and the Engine Control Unit (ECU). Have a look at the diagram above. The inputs to the ECU is marked green and the outputs from the ECU is marked blue.  Check that the brake light bulbs are OK, if not check the brake fuses. There are other inputs to the ECU from numerous other sensors or units for example the Automatic Gearbox Control unit, Cruise control unit, Air conditioning unit, Lambda Regulation unit, Knock Sensor units, Alternator, Engine Speed Sensor unit, ABS and the  Power-assisted steering unit to mention but  a few. 

The CAN-Bus bidirectional connection is marked in orange. Some of the other inputs like Knock sensors and Lambda regulator and Engine Speed Sensor unit can also cause the EPC light to come on. If the Engine Speed Sensor unit is responsible, it will reset itself after a while and if the Lambda regulation is faulty the vehicle will smoke and turn on both MIL and EPC lights, but if the Drive-by-Wire - DBW (not drive by cable) system is faulty then only the EPC light will be on.

Both the accelerator sensors and the throttle valve sensors work on the same principle since all 4 of them are potentiometers. The input voltage is 5 Volts and the increments are in millivolts implying that there is an  acceleration range of between 0 and 5000.  Throttle valve angle  sensor 1 and Throttle valve angle sensor 2Accelerator position sensor 1 and Accelerator position sensor 2 sliders makes contact with the resistive track and outputs the appropriate voltage level to the ECU. These resistive tracks are prone to go faulty since they are gold plated contacts running on gold plated copper tracks etched on a PCB. Over time the contacts wears right through the gold and copper plating, only making contact with the bakelite or fibreglass substrate. This type of potentiometers are less reliable than ceramic thick-film potentiometers.

When the EPC warning light goes on and your acceleration goes limp and the engine won't rev-up there is an easy cure but there may be exceptions. Get the car home even if it means driving really slowly in "Limp Mode". Once home, disconnect the battery for about 15 minutes or so, but not more than 20 minutes then reconnect. NB! do not disconnect the Live terminal, disconnect the Earth terminal. If the battery is disconnected for more than 20 mins you will lose your radio settings since the radio also participates in volatile and non-volatile memory of  the CAN-Bus

Reconnect the battery but make certain that the ignition is off. Once this is done, turn on the ignition so that the dashboard lights go on but do not start your car and DO NOT touch your accelerator pedal. After about 5 minutes the throttle body will aligns itself. After 10 minutes turn off the ignition, wait for 2 mins then start the car and let it idle for abut 2 minutes as well. By now, the EPC warning light should be off and the engine will rev as normal.You may have to to this twice. If this worked for you, please do give me some feedback with a comment.

VW Airbag diagnostics 

VW Instruments - Immobilizer


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EPC - Engineering, Procurement & Contracting, 
EPC - Engineering, Plant  Construction,
EPC - European Paralympic Committee,
EPC - Electronic Product Code, 
EPC - Event Promotional Council,
EPC - Energy Performance Certificate,
EPC - Engineering, Procurement and Construction, 
EPC - Event-driven Process Chain, 
EPC - Evolved Packet Core,
EPC - European Patent Convention,
EPC - Eastern Provincial Council, 
EPC - Electronic Poetry Center, 
EPC - European Policy Centre,
EPC - European Political Community, 
EPC - European Political Cooperation, 
EPC - Evangelical Presbyterian Church 
EPC - Export Promotion Council, 
EPC - Electricity Plant Controller, 
EPC - ElectroPlating Cathode,
EPC - European Payments Council,
EPC - Electronic Packet Collision,
EPC - Electrical Professionals Council,

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  1. Hi Idid what u said,but the light EPC still on,I switch off the car,next day I try to take the car with my friend, my friend his Mechanic,but he dnt know much about electronic,so we try to take de car to someone who know about this problem,but on the road we was surprised by the EPC that it wasn't on ,but after 10minute EPC come back but when we switch off the car EPC come off and back again after 10minute or more,my friend siad maybe is the wires,but I dnt know...and thx

    1. Hi anonymous, so sorry that resetting the ECU didn't work for you. It is quite common that the resistor unit on the accelerator pedal goes faulty, if your car has Drive-by-Wire. I described it in one of my previous blogs. The accelerator pedal isn't cheap even though its just a chunk of plastic but it is the Drive-by-wire G79 & G185 that is expensive. Try replacing it.

  2. Volkswagen Polo is compact and subtle but it doesn't mean that it compromises with the luxury.Its interior is comfortable and gives you a feel of being special.

  3. Component or end item comprising of a number of parts or sub assemblies put together to perform a specific function. It is amazing information but i think when a post is really good.
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  4. So my Brand new Audi TT 2013 only had 3, thousand miles on it and the EPC went on, and the acceleration goes limp and than wont rev and stalls out on the Highway, I call my salesman he calls audi for a tow assistance. Mean time AAA get their and cant figure out how to get the Toe Screw in and for that matter either can I , Hot Tip, you have to screw it in counter clock wise, Really ? Wow that threw me but after all it is a german car. So i took a picture of my brand new car while it was on top of the tow truck, thinking about that great commercial , you know the one , where he has never been able to tow the audi, and laughing as my entire day was shot, 5 hours latter i was at the dealership and I thought I might hear someone say, Im really sorry about this , but the reality was ho hum , and I had to leave it for a week, as they dont know what EPC code it is and they handed me the SABB rental car as a token of their gratitude but honestly I would have like the owner or manager to just say they were sorry instead of all the Laughter of the EPC code. It was cool everyone had a good laugh about them towing the car that could not be towed and was told how kias can go 100.000.00 miles without a hitch. Really / somehow i thought this problem might have been taken care of in the 2012 or 2013 but it is very much alive, and so that brings me to the quick fix when it happens again, and I am sure it will happen again as the laughter was to great at the Audi Dealership to ignore . WHAT IS THE EARTH TERMINAL and how often can i plan on having to EPC myself and Limp mode sounds like a blast , especially on the turnpike, in traffic and all, but this is good info and I truly thank you for it, but the LEGENDARY AUDI QUATTRO is slightly retarded from the EPC VIRUS> Now i know what the rings stand for but I am not in the right frame to say such things. Sunny Side Audi stinks

    1. Coal thanks for your comment and for relating your story about your Audi TT. And yes, I had a similar experience with my Volkswagen Polo hence I started this blog because of the incompetence that some VAG dealerships employ. As an electronics engineer I fixed my own car sinceI understand the functionality of ECU's and how they inter-communicate with the other electronic modules. I would highly recommend that VAG dealerships should only employ automotive mechanics with electronics experience, who understand binary numbers, hexadecimal code and checksums, electronic circuits, CMOS logic, Transistor switching, EEPROMS, microcontrollers and data buses, however they send their mechanics on a two weeks course then expect them to be able to do fault diagnosis and repair to replacement to electronics components (sensors and transducers and actuators) and program electronic modules of expensive cars. I've seen them grasp at straws, replacing sensor after sensor and module after module yet the error codes and faults remains. To come back to your EPC problem. EPC stands for Electronic Power Control and is directly related to the powertrain, meaning almost all error codes starting with Pxxxx could cause and EPC problem. EPC is a safety feature to prevent the car of getting out of control. One could compare the powertrain of a car to a horse that gets spooked by a snake and takes-off at high speed and runs uncontrollably with its rider totally unable to stop it. Certainly you don't want to be in a car that does this, so enter EPC. Follow my blog, I'm gonna do one on the TT.

  5. Hello Faried, I hope you can help me here,
    I bought a 2013 Kia Optima(2.4L Auto), The person whom i bought it from didn't tell me that the car had a accident in past, wasn't major, anyways, I bought the car, sent it for the car wash, They washed vallet the whole car, i picked the car up from them and as i came out of their drive way, it wasn't revving at all, It was driving on like 10Km/Hr speed, I took it back to them and they said they don't know anything about it.. anyways after a long fight i gave up and brought it back home and parked it in my yard, next day i took it to someone who had diagnostic tools and equipments, His computer came up with the fault code: TPS SENSOR FAULTY, LIMP HOME MODE SENSOR, i NEVER heard of these codes in my life, anyways i bought a new throttle body sensor and replaced, It didnt solve my problem, he said it could be my ECU,or wiring, I took to another guy who had all the scanning tools, he said its a Throttle body, I must get the body and the throttle pedal of the same car and then it can solve my problem, After a nasty week i managed to find him a throttle body + pedal of the same car, we put it in my car and the problem was still there, he then gave up and said take to the Agents where i knew i would be paying R500+vat per hour.
    next day morning i took the car to them, 4 days later i got a call from them saying my ECU is damaged, It cannot be repaired and the warranty is cancelled because of previous accident. They said new ECU would cost R25,000 and they cannot confirm after replacing the ECU it can solve the problem.
    I took the car back from them and took it to another guy who is specialized in reparing the ECU's, He said my ECU is fine but there is some other electrical problem, He can remove the codes from the ECU, Start the car, Take it for a quick spin, The car drives fine for about 10 mins, once you switch off the ignition and start the car again, it wont revv up, I am now SICK N TIRED of it, This guy who has my car now is so busy and does not have enough time to look into it,
    somebody said change the whole lock set of ECU, someone said change harnesss, if you are in johannesburg, can you help me looking into the car? or know someone who can solve the problem?
    please! my number is 0716987886

  6. hi, vw polo 1.4 tdi 2003 amf engine code. problem i have is that when driving at any speed, the engine looses power, no response from accelarator pedal, diesel glow plug warming light flashes, engine at 1200 rpm. turn engine off & then on again straight away, everything back to normal, no warning light, full power. can anyone shed any light on what this problem could be, thanks, steve

  7. Hi. I have a problem with my volswagen polo 1.4 Tdi. It seems to have a good start but after I drive for around 35 minutes it loses the power so I could not pass 2000 giro. Thank you for your suggestions.

  8. I am currently experiencing the same problem with my 2003 polo,1.4. The car goes into limp mode and on some occasions switches off in traffic, hectic ! I will use your method Faried. Thank you for saving me from going to a VW dealership, all i can do at this stage is do and hope

  9. My car is a polo 1.4 2012 model. Wen I start the car the epc light switch on then I put gear to move the car but it limbs then I switch it off then start it again then the epc light does not switch on then off I go... What could be wrong?

  10. thanks - worked for me, all lights gone out and car pulling away more smoothly now.

  11. I cannot say thank you enough for your advice/solution to this problem.
    I just did it step by step as in the procedure above and it worked on the first go.
    THANK YOU!!!!!

  12. Hi I have 2004 polo it starts but does not rev up took out negative terminal but still the same

  13. Hi, I have a 62 plate TSi SEL, The light kept coming on all the time and I had to start and stop the engine to clear it. Did what you suggested and the car has worked like a dream for the last two days. THANK YOU!!!

  14. worked 1st time for me thank you so very much - Ron Sydney Australia

  15. Also worked for my 2004 Polo 1.4 on the first try. I had the same issues with 'limp mode' and an EPC light that wouldn't go out. All resolved now. A real Christmas miracle. Thanks for the help! Thomas Canberra Australia.

  16. My post was chucked into the bit bucket so I won't comment again except to say that a car-crusher is the best tool for fixing problem Seat Ibiza, VW Polo 1.9 SDi and many other VAG products

  17. I have a '07 Polo 1.4 16v BUD. I dont have any lights on the dash, but the engine seems really weak through mid revs and is using a bit too much fuel. When I hook up my OBDII there are no faults recorded but when i view the throttle position in real time it doesnt seem to open in a linear manner.

    As I press the pedal on the road, the throttle valve seems to open slower than the position of the pedal. eg; 50% pedal = 30% throttle position, 80% pedal = 35% throttle, 95% pedal = 40% throttle, 100% Pedal = 100% throttle.

    As you can see WOT does give WOT at the throttle body, but I dont generally drive with my foot planted on the floor.

    I am confused why it does this as you would expect the throttle body to open the same amount as the pedal, could it need alignment? I am loathed to take it to the VW dealer for fault diagno$i$ so if anyone has any ideas????


  18. With the Polo 1.9 SDi engine there is another way. Buy an engine with the code AEF and bin the SDi. Not only does this get rid of the hated drive-by-wire system it also gets rid of the hated rattling dual-mass-flywheel. An even simpler way is to put the apology for a car through a car-crusher. Kaput Durch Teknik I call it. (The AEF code engines are hard to find unfortunately but the SDi types are plentiful on eBay. Draw your own conclusions!)

  19. Had the problem of no power, tried the technique described above (disconnect battery, wait, reconnect, turn ignition key, wait, turn off, turn engine on, wait, press throttle...) - and it worked beautifully. Many thanks for your help, very much appreciated - particularly as you've probably save me many pounds.

    1. Hi Steve. Nice to hear that this trick solved your problem. However, I don't want to be the bearer of bad news but the actual reason why your car went into limp mode is probably still stored in your car's ECU. Bear in mind that the act of disconnecting the battery does not erase the DTC. It would be in your interest to have it checked and remedy it by replacing the component that's causing this problem before it goes completely faulty while on a long distance trip. Cheers.

  20. Good day I have a problem with my vw polo 6r for a month now I took the car for a valet (interior wash) and I drove it hone from the shop I got and a few hours later I tried starting it didn't want start giving me a "no key" sign on the dashboard the car has been standing over a month now at the dealership and the warranty ran out about two months ago.....please help

  21. Hi Katta Kok

    The "no key" sign you describing is probably the yellow car symbol with a key below it, that flashes all the time which is accompanied by an audible sound. It appears that your immobilizer has been triggred which normally comes on when an unauthorised car key is used. It looks like your Instrument Cluster Anti-Theft Engine Disable Immobilizer require adaptation and the only way to communicate with the Immobilizer is by using a scan tool via address word 25. But before you do that, first try replacing the battery in your key fob.

    It is perfectly normal for the immobilizer ights to come on for about 3 seconds when ignition is initially switched on. During this short burst of time a very specific security data exchange automatic takes place between the pickup coil in the steering column and the key which is unique to your car.

    If an authorized key is detected, the alarm/immolizer controlled by the anti-theft system is switched off and enabling the car to start. However if a non-authorized key is detected, car will not start and display a flashing warning light. When the battery level in the fob key is too low for a complete and sucesful data exchange, the pickup coil / electronics in the steering column could interpret that data as an incorrect / unauthorised key. I hope its just that else it could be a fairly expensive repair.


  22. Hi Faried Manan
    I was at the dealership and said my key is a faulty I gave them the spare key (that was never used) and gave the same problem....They got new keys and a transponder and now they struggling to code they keys the technician says they struggling to pick up the vehicle on his laptop now I'm confused as the car is still not starting the engine crank but it doesn't want to start

  23. Hi Katta Kok

    I've recently uploaded a blog, so read through it carefully. If you dealer cannot pick up your vehicle there could be a short on the K-line that prevents communication. This is possible if you have an after market radio installed that's incorrectly connected. If they try to recode the keys, it only applies to the remote locking or doors and switching the alarm on and off only and not the immobilizer.


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