asc/abs faulty!

Your most likely cause is an ABS sensor. Would be difficult to find without a proper code read though.

Start by removing and cleaning all the ABS sensors and remaking all their connections. If that doesn't work, admit defeat and take it to a specialist with the diagnostics. If done already you would have saved the cost of an ECU!

In my case, it was a plugged filter in the Pentosin Reservoir. Relatively easy to replace.

This is the pentosin resevoir


And this is where its located

What are your tire sizes?

Terry raised an interesting point.

Your rear tyres are rotating approx 2% slower than front....and might be relevant to your problem.

The following tyre sizes give a much closer match.

Front 235/35R19
Rear 275/30R19
- OR -
Front 245/35R19
Rear 285/30R19

Latter might cause fouling issues though.........

There has been much written about this already - a lot of it by me just over a year ago when my own problem surfaced. There had been many helpful comments posted on the site already, but to be honest, this area is so complex and there are so many potential causes, that I felt that it needed a methodical approach. Someone also suggested to me that I check the wheel sensors. Sounded like a good idea, but I now know that this is a filthy and significant mechanical undertaking - and then, even when you have got to each sensor you have the problem of knowing whether and how it is failing. How do you test a sensor, for example? You could easily waste masses of time cleaning or changing all four sensors and then have the miserable experience, as many have, of finding that the problem is still there when you turn on the ignition. Alternatively, I could show you how to check all four sensors - and all the wiring to them - in less than the time it takes to make a cup of tea. And without getting your hands dirty!

As I crawled through the labyrinth of technology that is the Bosch 5.x ABS system, more than once I thought I'd found the solution:- the infamously incorrect "Eureka" moment for me was relays K94 and K95, which I honestly believed had been under-specced after a long conversation with a Bosch engineer... still smarting from that one! But in the end, with the help of the many useful suggestions I received from other members, I did get there. The faulty component was finally positively identified, was sent for reconditioning with a 2-year guarantee and has worked perfectly ever since. It was my ECU!

http://www.8er.org/forum/showthread.php?t=4707

Good Luck.

Smudge
On a 1997 Ci Sport the 2 relays K94 and K95 are situated in a box on the LHS (looking forwards) near to the bulkhead. They are coloured pink as original OEM parts. The performance of these 2 identical relays can be checked easily but for my money they are not your likely culprits. (If you have read the thread I quoted earlier, disregard any enthusiasm on my part about the significance of these relays). If you haven't read that thread, I recommend that you do so, because all of the other tips, mistakes and discoveries that I made (with the contributions of other, more qualified members) are contained therein. For me it was a question of whether or not I wanted to continue pursuing a series of "intelligent guesses", or find the root cause of my problem once and for all. I chose the latter course.
SG