ABS problem - light comes on and stays on.

[s2_bo]

Hello,

Got a problem with my ABS, for about a year now the light has been coming on very occasionally when turning corners at high speed. It then stays on until the switch is pressed twice, once to turn it off and again to turn it back on. The light then goes out and normally stays out.

But today it was a bit different. I went for a blast on the moors and after about a gallon of fuel and plenty of tight corners etc the light came on again. I then pressed it twice etc and it went off.
Then it came on again about 1 minute later while just driving normally. It continued to do this for the whole journey home so I did a couple of break tests.
Once with the light off - ABS on (supposedly), and the front wheels looked up and the car skidded to a halt even though the light was not on the ABS still failed.
I then did another test and the abs did engage but it coursed the light to come on and stay on afterwards.

Has any one got any ideas as to what could be coursing this intermittent problem? I have had a bit of a search but couldn't really shed any light on it.

Thanks.
Bo

[Acidburn]

(Scott Justusson)
A new sensor should be $5-$20 (allowing for Audi prices it is worth $1.50). If a sensor is bad, the light will stay off when the car is started, and then come on after driving the car from 10 feet to 2 miles. If the problem is elsewhere, it may turn the light on before moving the car.

To find the bad sensor, listen carefully after starting your car for unusual noises from one wheel. That's the one with the bad sensor. The noise is the ABS kicking in and out, until it decides to shut down. You can hook up a DMM to the sensor outputs, raise the car and spin the wheel. You get a square wave (A/C) from the sensor. The actual value is irrelevant, matching them is. Basically, you want to get the same reading from all sensors spinning the wheel approximately the same speed by hand.

I'd probably say a sensor is playing up on your car, this text should help from 20v.org

[shark_90]

ABS sensor sounds like the most likely place to start - could just be a loose/broken wire?

[Markarina]

had this problem when I originally got my S2, it turned out to be the diff lock switch, when you engage the diff lock you disable the abs and get the warning light

[Fat Audi 80]

You can also measure the impedance of the sensors I believe. 6k ohms from memory...

Have a search on here and the info is about.

Cheers,

Steve.

[Pirvu Eugen]

Iff is on all the time you can check also the blue wire from the alternator, this wire should give 12V with engine running for ABS unit. This aplies only to 3B engined S2.
But first Diff swich and sensors!

[Pirvu Eugen]

The sensors resistance should be between 600 and 1600 ohm.
Check for wheel bearing play and air gap off the sensors.

[s2_bo]

Thanks for all your help guys!! ill have a check tomorrow.

[s2_bo]

Cheers guys! Had all 4 sensors out today and greased them up before putting them back in. Have taken it for a spin and no faults so far.
Did a break test after the light stayed out. Emergency stop from 60 and all seemed good as the car came to a abrupt halt with out any tire screaming apart from in between the ABS break bursts.

Thanks again for all your input.

Bo