I've looked into it throughout the threads but haven't found someone with a problem like mine. When I start the car the abs light does not appear as I start driving it turns on then off sometimes staying on until I stop driving. I have and I assume this may be the cause of the problem because it started right after I had changed the deck in my car. I upgraded to a pioneer double din deck. I have a 1998 audi a4 1.8t quattro so if anyone knows anything any help would be great.

Thanks

 

search audiworld and elsewhere you get many instances of this.
it is a faulty ABS module that VM/Audi know about, however since it doesnt actually harm your braking (well, thats debatable) since only ABS doesnt work, brakes still do, there is no recall.

http://forums.audiworld.com/showthread.php?t=2797650

i am currently trying to VAG my car to confirm this problem, as i am having same issue

 

your e-brake has to be flashing too.

 

im assuming his ( ! ) light was accompanying the ABS light.
if not, check connections on all 4 brakes.

also, this is a good start:

"check the abs control module, it's located next to the windshield washer bottle, unplugg the conector and check it for corrotion, if there's nothing, plugged back in anc check, sometimes it's just a computer glitch, if not, u need to scan it to check the faults"