2002 A6 3.0 Q - ABS controller not communicating with ECU.
09-13-2018, 07:41 PM
#1
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2002 A6 3.0 Q - ABS controller not communicating with ECU.
Hello,
I have been having problems with the ABS Controller, not working correctly for over a year. I have spent tons of time to trouble shoot these problems, without any success. I am at loss at this time what the source of these issues is. I have replaced ABS controllers 2 times now, with used ones from ebay. The original one was causing weird issues, with intermittently and briefly (fraction of a second) locking the front right wheel while driving. The second used controller had worked for years.
To start, I live In Arizona where the summers are very hot. I have not had any issues with the car related to high temperatures for years. One day, after leaving the car on parking lot in the sun, when the temperatures were 110+, and not seeing any issues, upon returning I was not able to start the car. After several cranks, it started. Luckily, I was able to get back home. Since that time, I have had problems with cranking it intermittently. When stopped someplace, the engine would cut out (die) suddenly, and cranking it up again would take some time. I replaced the crankshaft positioning sensor (engine speed sensor). This seemed to fix the problem with starting up.
For some reason, right away when the sensor was replaced, the replacement ABS controller started to act up. Intermittently it was losing connection with ECU (ABS/BREAK lights on/flashing), was reporting problems with rear/right ABS speed sensor. I replaced this sensor with OEM one. It did not resolve the issue. I sent the controller to some supposedly reputable guy who said he can fix issues. When I got it back, the issues had gotten worse. The ESP light would flicker, ABS/BREAK flicker like a lights on Christmas tree. I disconnected the controller entirely.
Continuing the t-shooting, I replaced the ECU with a used one, newer version, but same part#. It was re-coded, adapted. Same issue with ABS controller not working right. So, I got a 3rd used controller, re-coded it, and it seems to act differently now. When engine is cold, the ABS and ESP lights are on. After driving, the ABS controller loses connection with the ECU. When, it communicated with the ECU, the VAG-COM showed:
01435 - Brake Pressure Sensor 1 (G201)
57-00 - Electric Circuit Failure
I disconnected this sensor. No change. The ABS controller still acts up the same way.
I read somewhere in this forum, that maybe relays could be causing some issues. I replaced most of 16 year old relays. No change. Still having issues with the ABS. The are no relays for the ABS controller anyway.
Also, I replaced the break light switch (F).
At this point, I don't know where to look for the culprit. Would anyone know?
I have been having problems with the ABS Controller, not working correctly for over a year. I have spent tons of time to trouble shoot these problems, without any success. I am at loss at this time what the source of these issues is. I have replaced ABS controllers 2 times now, with used ones from ebay. The original one was causing weird issues, with intermittently and briefly (fraction of a second) locking the front right wheel while driving. The second used controller had worked for years.
To start, I live In Arizona where the summers are very hot. I have not had any issues with the car related to high temperatures for years. One day, after leaving the car on parking lot in the sun, when the temperatures were 110+, and not seeing any issues, upon returning I was not able to start the car. After several cranks, it started. Luckily, I was able to get back home. Since that time, I have had problems with cranking it intermittently. When stopped someplace, the engine would cut out (die) suddenly, and cranking it up again would take some time. I replaced the crankshaft positioning sensor (engine speed sensor). This seemed to fix the problem with starting up.
For some reason, right away when the sensor was replaced, the replacement ABS controller started to act up. Intermittently it was losing connection with ECU (ABS/BREAK lights on/flashing), was reporting problems with rear/right ABS speed sensor. I replaced this sensor with OEM one. It did not resolve the issue. I sent the controller to some supposedly reputable guy who said he can fix issues. When I got it back, the issues had gotten worse. The ESP light would flicker, ABS/BREAK flicker like a lights on Christmas tree. I disconnected the controller entirely.
Continuing the t-shooting, I replaced the ECU with a used one, newer version, but same part#. It was re-coded, adapted. Same issue with ABS controller not working right. So, I got a 3rd used controller, re-coded it, and it seems to act differently now. When engine is cold, the ABS and ESP lights are on. After driving, the ABS controller loses connection with the ECU. When, it communicated with the ECU, the VAG-COM showed:
01435 - Brake Pressure Sensor 1 (G201)
57-00 - Electric Circuit Failure
I disconnected this sensor. No change. The ABS controller still acts up the same way.
I read somewhere in this forum, that maybe relays could be causing some issues. I replaced most of 16 year old relays. No change. Still having issues with the ABS. The are no relays for the ABS controller anyway.
Also, I replaced the break light switch (F).
At this point, I don't know where to look for the culprit. Would anyone know?
09-14-2018, 02:55 AM
#4
AudiWorld Senior Member
Have not had any of these issues, but I seem to remember reading that an aftermarket radio an cause the ABS to malfunction. Have no idea why.
09-14-2018, 07:24 AM
#5
AudiWorld Senior Member
Check the wiring in the vicinity of the wheels. A bad wire or connection at the wheel speed sensor(s) can cause this issue. Had it happen to me. When I had a scan done it reported "faulty pump, right front". ABS controllers are known to develop issues on the circuit board. Module Masters in Moscow, Idaho can repair ABS units if the control unit is actually the problem. Around $300. I had them repair my center display on the dash a couple of years ago. They have a great warranty on repairs and usually quick. I had my dash back up and running in less than two weeks.
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