David.Norton

I had exactly those symptoms, the car would stall, then not start, then randomly work again (of course the gas cap then becomes a red herring). Interestingly mine was also a chipped ECU. I had the original in the garage, plugged it in and the car has been working fine for the past year, although I do miss my chip.

SilverHotz

As I mentioned above, I can't currently scan the car. It won't talk to my laptop. I tried the same laptop and VAG setup on a friend's 97 A4 and it worked so I think the same problem that's keeping the car from starting is causing it to not scan as well.

When I pulled the codes before when the problem was more intermittent The only code was "P1602 18010 Power Supply (B+) Terminal Supply 30 Low Voltage".

I'll try cranking it again tonight when I get home and see if the check engine light is on or not. The ECU being bad or not getting power makes sense at this point since my laptop won't communicate with it all of a sudden.

jseklund

How long has it been not starting now? Could the battery be weak?

Sounding like an ECU issue...but we're grasping at straws

SilverHotz

I had a battery tender on the car since the issue occurred since I was doing a lot of cranking without starting so the battery should be topped off.

I tried starting the car last night and the check engine light does not illuminate at any time. I checked the +12v terminals at the ECU and they are both showing 12v and both grounds for the ECU seem good as well.

I checked the ground at the fuel pump relay and it seems to be an issue. The +12v and chassis ground shows +12v, but if I use the ground for the fuel pump relay I see +6.5v with the key on and +8.5v while cranking. I'm guessing if I put any load on that it would probably drop right to 0.

I also scanned the ABS module and that worked fine. I tried again to scan the engine module and it would not communicate. It seems like it's the ECU. I'm trying to hunt one down locally. APR did the chipping and my buddy seemed to think they may offer lifetime warranty so I'm going to look into that but I'd like to find a stock ECU to verify that is the issue first.

jseklund

Where are you located? Maybe there is someone on here local that can swap one out with you just for testing purposes? Not sure if there are coding issues...

audiqv8

The ECU control the ground to the fuel pump. It will only supply the ground if it see the engine running. Sound as though you have a bad ECU.

SilverHotz

There is a 10-digit number on my ECU: 4B0 906 018 P

Is that what needs to match for a replacement or are there more numbers that must match or maybe only some of those number must match. Anyone know for sure? I think I found a replacement on Ebay for $110 but I want to make sure it's the right ECU. The two local suppliers both came up dry.

SilverHotz

I replaced the ECU with a used one I found on Ebay and nothing changed. Still no check engine light with the key on and it still won't start. I guess it's back to the drawing board...

audiqv8

One last try, disconnect the ICM (Ignition control module), then turn the key to the on position, but don't try to start it. Is the check engine light on? Can your computer communicate with the ecu?

SilverHotz

I'll check out the ICM today. One more question though. The ECU I bought should work without any programming as long as it's the exact same part number. I verified all 10 digits match and it also matches the part number I found on the forum for my year, engine, trans and quattro configuration so I'm almost certain it's the right ECU. I just want to verify that no programming should be required.