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Discussion Starter · #1 ·
I recently picked up a used 2003 B6 Avant with some known issues. Replaced the AMB head for an AWP head and now it runs. Now I’m delving into the electrical gremlins.

Airbag, ABS, and BRAKE lights. Airbag is an open circuit crash sensor. Should be a fairly straightforward fix. ABS was a 00301 (v39) ABS pump. After an afternoon of reading I decided to start by wiggling fuses. Now I have no response on VagCom from the ABS module. Also a new development are brake lights that remain on if ignition is on/car running but not on if key is removed. If not running or in accessory the actual brake lights will function with the pedal as they are supposed to do. So that steers me away from a simple brake switch. Same time as the perma brake light development the speedometer stopped working that has me guessing it's tied to the lack of coms with ABS module. No power, no coms. Likewise this year model uses the front driver's ABS sensor for the speedo. I’ve also observed multiple new DTCs relating to grounding issues as well as an OIL SENSOR dummy light blinking that showed up same time as the fuse wiggling. Really wish I had not wiggled fuses now.

Then there's this one: 00668 - Supply voltage terminal 30

That’s the one that I think should fix all but ABS pump and airbag and take me back to square one before the fuse wiggling. I suck at determining which electrical diagram I need but if I have the right one I can figure it out. Been rummaging through my Bentley but to no avail. I’ve checked all the small fuses in the side panel and they are good. Fuse 42 does not read 12v~, but 0.4v. This bothers me. All other ABS/traction control and/or brake fuses are at full power. Two big fuses under dash (50a and 60a) are not blown and reading 12v across. I pulled relay 167 but don’t know what I’m looking at to check it so I reinstalled it. I feel it's a relay but there's only three under the dash.

I had a simple fuse go out on my mk4 Jetta once and it took the o2 sensor, EVAP, and MAF out with it. Initially it looked like the fuel relay but I tracked it down to a ever so slightly blown fuse. This seems similar but not. Are there any other fuses I am missing that are not in the cabin?
 

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a while back, my girlfriends car had similar issues. she had a blue b6 1.8TQM that was tuned. she had airbag, brake, and abs lights on and her speedometer stopped working. the airbag light was because the crash sensor in the B-pillar is susceptible to water damage and corrodes internally. replacing that (like you said) should be pretty straight forward. as for the brake, abs and speedometer problems, i was experiencing similar instances. I believe I also had supply voltage to terminal 30 at one point (i cant remember), but her speedometer would sometimes work fine, other times it would just stay at 0 until one day, it just stopped working all together. I saw a lot of people saying it was a wheel speed sensor issue, but when I couldnt connect to the ABS module with Vagcom, I decided to look at the abs module itself. I took the ABS controller off of the pump and cut it open to expose the electronics and found that one of the angel-hair-thin wires that was potted in gel had broken. I thought about trying to repair it since I have experience with soldering, but when I realized it was way out of my skillset, I opted for buying a used ABS unit from ebay. i made sure the numbers on the existing module matched the one I purchased, and only swapped the electronics portion. it came with the pump and the distribution block, but I didnt want to deal with bleeding the brakes. once installed, the unit recognized it was in a different vehicle and wiped its programming on its own (this is for safety reasons and normal) and I was able to re-program it. after that, she never had another abs, brake, or speedometer issue ever again.

TL:DR

replace the module. get it off ebay and make sure the numbers match (it will save you a ton of money). you will have to reprogram it, but it should solve your abs, brake, and speedometer issues. I would also guess that your brake light issues are probably also related to the abs module.
 

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Discussion Starter · #3 ·
Thanks for the reply. I’ve cross posted as well at AZine to speed the process.

I’ve found some solutions to most of my issues. The fuse box in this car is completely corroded and I wiggled fuses looking for better contact which lead to no contact, intermittent contact, and partial contact. Most all of my issues were caused by the fuse box. Once I grasped what was going on by studying the Bentley diagrams I was able to link the majority of issues on fuse #7 and #34. The tip off was when the injectors went open circuit after a fuse wiggling. They pull off of #32. At this point I pulled all the fuses, tossed those that did not look 100% on the prongs, air hosed the fuse box, flat pencil filed each connection, air hosed again, WD40ed all of them, air hosed again, dielectric spray, air hosed, and put the fuses back in. Cleared codes and now just have three recurring DTCs.

-ABS pump (think my old Jetta has the same and hopefully just swap the pump)
-pressure drop between turbo and TB (hood cable pulled off release latch, will look into that today cause n249 is deleted and wasn’t an issue until recently)
-coolant sensor bad: g62 (the hard to reach one on the Quattro)

Fuse #34 touches so many systems it is completely silly: EVAP pump(v144), EVAP valve(n80), MAF(g70), SAI valve(n112), SAI relay(j299), turbo recirc(n249), both o2 sensor heaters.

The ABS circled back to fuse #7.
 
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