Brakes won't disengage ... now ABS communication issues!
#1
06-15-2022, 05:12 PM
Brakes won't disengage ... now ABS communication issues!
Hey y'all,
A couple of weeks back the brake pedal on my 2002 A4 3.0L Quattro (6 spd) got stuck in the engaged position and the car wouldn't move, even when giving it a lot of gas and risking total burnout of my relatively new clutch. After a quick brainstorm, I simply used my toes to pull the pedal back into the normal resting position and the brakes disengaged. I was able to drive it the short couple of miles home with no issues. The pedal felt fine and had no repeat for a few more days. Then it happened again. Same as the first time, I was able to pop it back using my toes. The third time it was more difficult to pop it as I actually had to use my hand. The fourth time, I was not so successful as I was not able to get the pedal unstuck. Thankfully it was in a friend's driveway so we let it sit overnight. The next day we were able to get it unstuck enough to drive it the one mile home, brakes somewhat engaged the whole way but at least it was then in my own driveway. I got it towed to my local independent german shop. Their initial diagnosis was the m/c. The pedal never felt spongy like I would expect from a m/c failure so I was skeptical, but had them replace it anyway. Unfortunately, that didn't fix the problem. In an attempt to further troubleshoot, the guys at the shop tried to evaluate the ABS module by unplugging the ABS wiring harness and driving it around a bit. They relieved the pressure using the bleeder screws and allegedly had no issues after driving it around a bit. I convinced them to let me drive it home to get it off their lot while they searched around for a reasonably priced replacement option. On my way home with it, the brakes kept getting tighter and tighter with each stop, almost to where I could barely drive it by the time I got back to my driveway, ABS unit still unplugged.
Now to complicate things, I decided to plug the ABS module back in and see if the ABS was throwing any codes using my vagcom (thank you ross-tech!). Now I'm getting codes that seem to indicate the ABS and ECU won't communicate. Note, I scanned it before the flatbed picked it up and did not have any of these codes present before the shop touched it!
I'm all ears. My wife is about ready to tell me to scrap the car.
thanks,
Matt
A couple of weeks back the brake pedal on my 2002 A4 3.0L Quattro (6 spd) got stuck in the engaged position and the car wouldn't move, even when giving it a lot of gas and risking total burnout of my relatively new clutch. After a quick brainstorm, I simply used my toes to pull the pedal back into the normal resting position and the brakes disengaged. I was able to drive it the short couple of miles home with no issues. The pedal felt fine and had no repeat for a few more days. Then it happened again. Same as the first time, I was able to pop it back using my toes. The third time it was more difficult to pop it as I actually had to use my hand. The fourth time, I was not so successful as I was not able to get the pedal unstuck. Thankfully it was in a friend's driveway so we let it sit overnight. The next day we were able to get it unstuck enough to drive it the one mile home, brakes somewhat engaged the whole way but at least it was then in my own driveway. I got it towed to my local independent german shop. Their initial diagnosis was the m/c. The pedal never felt spongy like I would expect from a m/c failure so I was skeptical, but had them replace it anyway. Unfortunately, that didn't fix the problem. In an attempt to further troubleshoot, the guys at the shop tried to evaluate the ABS module by unplugging the ABS wiring harness and driving it around a bit. They relieved the pressure using the bleeder screws and allegedly had no issues after driving it around a bit. I convinced them to let me drive it home to get it off their lot while they searched around for a reasonably priced replacement option. On my way home with it, the brakes kept getting tighter and tighter with each stop, almost to where I could barely drive it by the time I got back to my driveway, ABS unit still unplugged.
Now to complicate things, I decided to plug the ABS module back in and see if the ABS was throwing any codes using my vagcom (thank you ross-tech!). Now I'm getting codes that seem to indicate the ABS and ECU won't communicate. Note, I scanned it before the flatbed picked it up and did not have any of these codes present before the shop touched it!
ECU Code: 18057 - Powertrain Data Bus | P1649 - 008 - Missing Message from ABS Controller - Intermittent
ABS Code: 18256 - Please check DTC Memory of Engine Controller | P1848 - 35-10 - - Intermittent
Instrument Code: 01316 - ABS Control Module | 49-10 - No Communications - Intermittent
An ABS module is both hard to come by and expensive so I want to make sure I've exhausted the troubleshooting options to validate the ABS now needs to be replaced AND that replacing it will fix my issues. I totally understand that my shop may have fried the ABS somehow and so now I have two problems.I'm all ears. My wife is about ready to tell me to scrap the car.
thanks,
Matt
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