EPC Q & A

EPC Q & A

So many Audi, VW, SKODA and SEAT owner are having EPC light nightmares. Sending their vehicles for EPC repair which are often misdiagnosed, costly, ineffective and futile because most mechanical repair personal are not electronically trained hence have no idea of  digital logic and isolation procedures.  Modern cars are strewn with sensors and actuators, network buses, electronic control modules driven by software. To quote a line in Turks and Caicos which goes something like this "... everything changes. I used to be able to take a wrench and get under my car's bonnet and fix my car. Now you need a degree in electronics. Even easy things are difficult now." Replacing automotive components does not have to turn into a 'wild goose chase' where guess work is based on trial and error which now has become the order of the day.  That approach just scares everyone. Upload the diagnostic scan of your car now, so that I can analyse for you before you go ahead and buy expensive parts only to find out that the DTC was incorrectly interpreted.

Question?

I'm Lorraine from long beach. I don't know who you are but you are a God to me. I've been searching the web for months for specific and in-depth information on the "death light" (EPC) appearing on my '99 Volkswagen  Beetle. I have studied your entire blog and will now have a very interesting conversation with my German Car mechanic on how he can detect once and for all the problem. Already $1,000 in with no results. Thank you. I hope I don't have to sell the car just yet (to whom, I have no idea) throttle body replaced-twice so far-but hmm that Cam Bus section is interesting. My radio went into Safe Mode months ago and then spontaneously came back on (we do not have the code) so maybe we should check that path out as well. Again thank you.

Answer!

Hi Lorraine, since you don't say much about the specific problem that you are having other than the "death light" (EPC) appearing on my '99 Beetle, I really can't comment on it. However since it is EPC related, your problem has something to do with fuel delivery and engine torque electronics. Bear in mind that your fuel is under pressure from the tank to the injectors and that the ECU receives inputs from the various pressure sensors. If any of these pressures are below spec, it can trigger an EPC problem. For example, if your fuel cap does not seal properly the low fuel pressure sensor G410 will send a error signal to the ECU which can trigger an EPC fault. Likewise if the fuel regulator sensor cannot equilize the fuel pressure from the high-pressure fuel system it will trigger an EPC fault. Suppose If you were driving on an incline like an on-ramp to a bridge and didn't gear down sufficiently for you Beetle to swiftly climb with ease, the likely hood is that detonation would occur. If this happens, the knock sensors would inform the ECU which translate detonation as insufficient torque and trigger the EPC circuit - limp mode and EPC light. There are several other EPC possibilities but without a diagnostic scan it is difficult to pin point the problem.

Question?

Anonymous. I have a '07 Polo 1.4 16v BUD. I don't 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 doesn't 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 don't 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???? Thanks

Answer!

Hi there. Since you don't have  diagnostic scan its difficult to help you however, the mere fact that you don't have dash light makes it very obviously that you have electrical problems or wiring harness problems. And since your scan tool didn't find any DTCs, further proves that this is the case. The dashboard is normally directly connected to the OBD port in the driver's cockpit and since you have no dash lights you most likely have missing voltages on the OBD port which is most likely needed to perform a proper and correct diagnostic scan. Check your fuses on the terminal 30 line and the relay that supplies the terminal 15  supply line. Once you've exhausted everything else, as a last resort your dash control module could be faulty. Anyway, the acceleration peculiarity that you are describing probably has nothing to do with the dash electronics. Since you car has drive by wire, which is totally electronic (not throttle cable), torque is determined by the ECU which will open the throttle valve logarithmically based on its load and terrain, thus there is no physical correlation between the accelerator pedal and the throttle valve. So, no I don't think it needs alignment but seeing you have an OBD-II scanner, its quite simple for you to just redo the adaptation (described in a previous blog) and take consolation in the fact that you have eliminated it as a problem.

Question?

Hi I have a problem with EPC it came on since yesterday, am worried please help.

Answer!

My friend, you really not giving me much to work with here. But I suggest that read through my blogs pages related to EPC, torque, drive by wire, accelerator pedal sensors, knock sensors,  throttle adaptation, engine RPM sensor, etc. Perhaps if would shed some light on your EPC problem. Remember that EPC problems are related to what the car was doing at the time the light came on. for example, spirited driving / towing / start stop peak hour traffic, etc, Anyway the best way to find blog pages relating to your EPC problem , is to type your search word (EPC / drive by wire, etc) in the search box I provided in the top left hand corner on the first page of my site and click on the miniature magnifying glass to run the search. Happy searching.

Question?

Hi everyone, I would really appreciate some advice from you all. I have a 2002 (52) Ibiza 1.4 Sport (100bph), and have some issues with it. Background: Since day 1 it has occasionally thrown up an EPC warning light, followed by an engine electrics light. They would go away after a day and not return for several months. I had the logs read by a Seat dealer during a service and they said it had shown an intermittent Lambda filter error, and that it would cost £240+ to fit a new one. I passed. Over the last month, this has become an every day occurrence. The EPC light will come on seemingly as I just try to pull away from stationary. The car sometimes (half the time) notably stutters when this happens, then pulls away normally. If I restart the engine, most times the EPC light will go off, but the engine light will stay on. Then, more weirdly, the car has started occasionally stalling at random. No judder, no rough idling, I'll be slowing down towards a roundabout or into traffic, and whilst idling (coasting on the clutch) as I slow down, I'll notice the battery light come on, and the power drop out. Once, the battery light came on, but I was able to rev the engine up and it recovered - the battery light then went out. Mostly, I need to restart the engine though. I took it to a garage called Vee Ws for its annual service yesterday and asked them to look into it as well. They went with a cautious (on my finances) approach, and said they'd do the full service and that hopefully that on its own might rectify some of the issues. After the service, they said the logs showed some intermittent issues but nothing serious. They reset the onboard computer to its basic/default settings and said they hoped that would sort it. They also said they noticed the throttle body was pretty dirty (done 71,000 miles), and that if the service doesn't sort it, that they would try to clean that up and see if it did the job. Anyway, 10 minutes after I pulled away from the garage, the lights came back on and today the stalling re-occurred. I feel like this could turn into one of those 'wild goose chases' where its a case of trial and error, replacing different parts to see if it works. This scares me greatly! Has anyone experienced any similar symptoms, or would anyone recommend going to a proper Seat Dealership/Services team to take a look? I wonder if maybe they may be more likely to find the underlying fault? Having said that, I've always found Vee Ws in Bristolonia competent and most importantly, cost-effective. It may be possible to ask them to try and source used-parts while they try different 'fixes'.. Thanks for any advice, Jamie

Answer!

Hi Jamie,  the fact that your SEAT occasionally throws up an EPC warning light, as well as  the engine electrics light, says that your problem is more likely emission related, hence your intermittent Lambda error. Normally only torque and fuel related problems triggers the EPC light, meaning the engine light doesn't come on. Engine light only comes on with emission related issues.  Considering the age of your car it is possible that the Oxygen censor could be glazed over (end of life) or its wiring connector could be intermittent. The oxygen sensor is a feedback mechanism that instructs the ECU to increase or decrease the fuel supply hence shuddering. But this may not be definite. Without a diagnostic scan, I  am more inclined to say it could be your throttle body sensors not only because your service agent said it was dirty but because of the stalling and stutters on pull away. This seems like the throttle valve isn't providing an adequate air supply when its needed. However if they serviced your SEAT and did the adaptation as they said they did, then its unlikely the throttle body else adaptation would have failed, even though they said its dirty. So its more likely to be your accelerator pedal sensors. I mention this because  the car switches off when you decelerate, implying while your foot was on the accelerator it was OK but by taking your foot off the accelerator the condition changed and the ECU picked of this which could be due to 1 or both intermittent potentiometers. When you initially start the car  the ECU does a self-test by switching on all dashboard lights and if no problems are detected turns them all off. So when you start and the EPC light turns off, at that specific point in time there is no problem, but half way through acceleration while driving the problem is detected and the ECU switches he car off. Intermittent DTCs that do not reoccur during four driving cycles, are automatically deleted from the system which explains why the EPC light goes out after a day or so and doesn't show up months later. Lets have a diagnostic scan and I will have another crack at analyzing your problem.