ABS & Brake Light Warning After Battery Failure
 

My son let his '97 A4 1.8t sit for a couple of months and the battery went dead. He jumpstarted his car and just about every warning light went on and he also blew the integrated fuse on the Delta radio. I cleared all the engine DTCs with a std ODBII scanner, but my ABS and BRAKE warning lights are still on. I had a VAG cable laying around and tried Ross-Tech shareware, as well as a U280 code reader, but neither seems to be able to communicate to the ABS module (though they can communicate to the engine). I've tried disconnecting and reconnecting the wiring harness to the ABS module, but that doesn't help either. I know the ABS modules on the B5 are prone to fail, but aren't these mechanical failures and not electrical failures? Just seems odd that the ABS module would fail from a dead battery/jumpstart. Any other ideas before I try getting the ABS module rebuilt?

I had forgot to check the main fuse panel and found that two fuses associated with ABS were also blown. So, I replaced those and finally got VAGCOM to communicate to the ABS system and it came back with a 65535 error and neither of my scanners would allow me to clear it. So, is it likely that I need my ABS module rebuilt or is this some other problem?

I ended up disconnecting and reconnecting the cable to the ABS module a few times over a span of a day. Finally, I could heard a bunch of relays click when I reconnected it. The idiot lights went out, but reappeared shortly later, but I could then clear everything with my VAG and it seems to now work.

Same thing happened to me
 

The exact same thing happened to me!!! I hadn't driven my TT since the beginning of Covid 19 and I jumped it with my other car then it wouldn't hold the charge so I replaced the battery. Then the ABS light came on and brake light began flashing. I took it to a mechanic today and he said that it was going to cost me thousands of dollars to fix. He gave me the code P1649. Not able to communicate with ABS control module. What should I do?

Did you do what the other post said to do and check your fuses?

Hi,

I would also try swapping in a new battery or a different battery from another car in addition to what I did before.