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B6 Forum 2002-2005 Audi A4 & Audi A4 Cabriolet / 2004 Audi S4. (Audi A4 Forum, Audi S4 Forum, Audi RS4 Forum)

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Old 10-14-2005, 04:26 PM   #1 (permalink)
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Approx 1 hour into the journey, when you try and accelerate the EPC light comes on and the throttle is cut out. After 5 or so seconds the light goes off and the throttle works again. This has hapened in excess of 20 times and the car has been to the dealer 4 times. Anyone else had the problem???
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Old 10-17-2005, 06:39 AM   #2 (permalink)
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Have you done any adjusting of the brake pedal sensor lately? Might be a problem with that.
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Old 11-02-2005, 10:14 PM   #3 (permalink)
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smats . . .

i have the same problem on my 2000 s4 . . . sometimes, when punching the pedal all the way to the floor while at low rpms, i get a sudden power loss accompanied by the epc light . . . if i shut the car off, it corrects the problem . . . it's like a tripwire that puts the car into 50% power mode, and it's actually pretty dangerous . . . when i floor it, it's usually because i need to, like to get in front of a semi while merging onto the freeway . . . not a good time to lose power.

anyway, i went to a local mechanic who specializes on german cars (audi/bmw/porsche), and he determined the problem was caused by the throttle position sensor . . . we ended up replacing the throttle body which had a defective micro-switch.

all is good for about a month and then it starts happening again, although much less frequently . . . so, my car is in the shop again right now and the mechanic is trying to diagnose . . . when the light goes on, the computer is indicating an incorrect throttle position and a "lean condition", meaning the fuel/air mixture isn't right, or at least the car's computer thinks it's not right . . . the mechanic thinks it might be a problem with the air mass sensor, but i've been reading up a bit, and i think it might be caused by loose wiring/connectors on the throttle pedal itself, which would be rather amusing after all the sleuthing . . . dark comedy if you consider the $

cheers . . . let me know if you find anything on your side.

bd

Last edited by taoofthe777; 08-21-2009 at 04:35 PM.
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Old 01-06-2006, 02:54 PM   #4 (permalink)
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I recently had this same problem on my '02 A4 1.8T, on the way home from work. The car went into a limp-home mode which limited the amount of throttle opening, revved very slowly up to about 5K and would not upshift past 2nd gear unless I manually shifted up. Speed was limited to about 40 mph, and acceleration was very slow. Several warning lights came on at once, including check engine, EPC (what does this mean??), and the ESP warning light.

I drove the car back to my office and took a company pool car home that night. The next day when I took it to my local dealer, the problem had gone away. They were able to retrieve the error codes, which indicated some error in the accelerator pedal sensor. They did not replace the part, only cleared out the codes.

The problem recurred about a week later. In this case, the EPC and ESP warning lights came on, but not check engine. I stopped the car, turned it off for about 1 minute, then re-started and the problem went away. So far, I have not returned it to the dealer again.

Not sure what the root cause is - loose wire, poor connection somewhere in the harness, or bad pedal sensor?? In both cases, it was raining outside, so I'm a bit curious if water is getting into some electrical connector somewhere and causing a short. This car has a throttle-by-wire system, which has several different safety back-up strategies in case of a fault anywhere in the system. But it's very annoying if some simple harness issue is causing it, and especially since the dealer seems willing to simply clear the codes without doing a deeper investigation into the root cause. It's no longer "safe" if you are expecting to be able to accelerate out of a situation, and there is no power to do it.
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Old 02-07-2006, 07:01 PM   #5 (permalink)
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Hi, glad to see it's not just me who has had this problem.

I had similar things happen, the EPC light would come on, I would lose power and it would not right itself until the engine was off. On re starting it would be fine, this continued for a while until eventually the car was permanently in "Limp Home" mode. My mechanic tells me this is because the on board computer can only hold so many error codes and when it's full it will not correct itself until cleared.

On clearing the codes we changed the air mass meter and the throttle switch potentiometer (accel pedal with a black box on the end) Job done, problem fixed. 3 months later, started again.

Someone told me to do the following and it has been fine ever since.

Apparently you can reset the potentiometer by

Engine off, turn ignition to 2 (dash lights) press hard on the accel pedal on off 10 times. Leave a few seconds, keys out of ignition then start the car.

fixed the problem....

Al
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Old 03-06-2006, 06:22 AM   #6 (permalink)
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Hi I am very interested in knowing if that REALLY solved the problem or just temporarily postponed it? I had the same problem and solved it using the ignition on and off. It just happens once in a while. I will try your method but please keep us posted as to whether it relaly did solve the problem or not. Thanks.

Audifan
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Old 04-25-2006, 12:15 PM   #7 (permalink)
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Greetings, I experienced a problem with engine power loss on a trip this past weekend. I had been driving for a couple of hours, stopped to get gas, and a couple of hours later I experienced the power loss on the Interstate Highway. My EPC and Check Engine lights came on and I had no acceleration. I pulled off the highway, turned the car off, checked the gas cap, restarted the engine, and the problem was corrected.

A couple of hours later it happened again. It was pouring rain and I was only about a half hour from home, so I kept on going. I dropped a friend off, restarted the engine, and even though the Check Engine light was still on I had normal acceleration.

The next day when I left for work I still had the Check Engine light and normal acceleration. Today, I have no Check Engine light and everything seems to be fine.

Very strange. I am reluctant to take it to the dealer because it is out of warranty and it sounds like everyone else is having trouble diagnosing this problem. I will try Newbie's suggestion for clearing the errors and monitor the situation.

Andrea
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Old 04-25-2006, 01:00 PM   #8 (permalink)
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Hello again,

I had the same problem repeat several more times since my original posting on Jan 6. Each time the problem occurred, it was raining heavily (although it didn't happen each time it rained). Of course, I could only take it back to the dealer while the problem was actively happening, otherwise if you bring it in after the fact they don't seem to do as good of a job in trying to fix the problem, they will just clear out the codes.

The first time I took it back, the dealer replaced the accelerator pedal module, which I suspected would not fix the problem. (I suggested that they look at the wire harness closely, which I suspected was getting some water intrusion and resulting in a short circuit or ground fault. But they didn't follow this recommendation - they basically started replacing parts.)

Sure enough, about 3 weeks later the problem occurred again when it was raining. This time I made it very clear to the dealer that they needed to look at the wire harness closely, and in fact they found some corroded terminals in one of the harness connectors. They replaced this wire harnesses and so far the problem hasn't come back (about 4 weeks now).

Andrea - since your problem also occurred while it was raining, I suspect your problem is similar to mine. My problem would always correct itself after the car sat for a while and dried out. Occasionally simply stopping and re-starting would also correct it, maybe 25% of the time. I would recommend getting it fixed even if it's out of warrenty, because it's not a safe condition to be in, if you suddenly need to have engine power available and it isn't there. In order to reduce the potential for repeat visits to your dealer, make sure they look closely at all of the wire harness connections, as opposed to just swapping out parts.
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Old 04-25-2006, 01:00 PM   #9 (permalink)
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i have heard in the past the air mass sensor can put the EPC and traction light on..

i will have a look for the post..
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Old 04-26-2006, 12:53 PM   #10 (permalink)
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tszczotka, thanks for your update. You are right, it is not safe and I will take the car to the dealer with your advice about the wiring harness. It makes sense to me that this could be a moisture problem with the electrical system. It was raining cats and dogs when this happened during a long trip. I typically drive short distances so a problem like this would not show up normally.

It's great to have the background information from the forum so I can discuss the problem with the mechanic.
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