ABS light on

[ujimaflip]

OK - I know there are already a lot of threads on this already... I've not used the S2 in quite some time - and the battery was flat. I managed to get it started, but the ABS light refused to switch off (I can switch the diff lock on and off). I read somewhere on here that the ABS may refuse to switch on if the battery was flat - so I've charged it up - the light still stays on.

I've checked fuse 31 - definitely OK. Most other threads talk about an intermittent problem - this is permanent (I've now driven a few hundred miles - the light has never gone off). And before anyone asks - I've tried pressing the switch to turn it on and off

Any other ideas before I take it to a garage?

Thanks

[S-Express]

wire brush on the abs hub rings and blow and cr%p off the sensor too - your problem is probably corrosion of one of these rings

[ujimaflip]

This is when you find out what a novice I am...

Not sure which bits are the abs sensor and hub rings... Last car I maintained was a 1980 Escort sports... Nothing fancy like abs. Any guidance you can give me?

[20vQC]

OK - I know there are already a lot of threads on this already... I've not used the S2 in quite some time - and the battery was flat. I managed to get it started, but the ABS light refused to switch off (I can switch the diff lock on and off). I read somewhere on here that the ABS may refuse to switch on if the battery was flat - so I've charged it up - the light still stays on.

I've checked fuse 31 - definitely OK. Most other threads talk about an intermittent problem - this is permanent (I've now driven a few hundred miles - the light has never gone off). And before anyone asks - I've tried pressing the switch to turn it on and off

Any other ideas before I take it to a garage?

Thanks

I have that problem exactly as you explained! I had the car on the garage for 7 months and the light does not turn off yet. I'll do later the job that S-Express wrote here.

cheers!

[S-Express]

Not sure which bits are the abs sensor and hub rings... Last car I maintained was a 1980 Escort sports... Nothing fancy like abs. Any guidance you can give me?

Ok - remove road wheel, look behind hub and you should see a ring attached to the hub/driveshaft. This will either have ridges on it or holes in it and a sensor about 3mm away from the ring. The holes/ridges are detected by the sensor and allow it to know that the wheel is turning (or not).
Corrosion builds up around the rings and confuses the sensor - cr%p can also build up on the end of the sensor as it is normally magnetic.
If all 4 hub rings and sensors are clear of debris AND the sensors are all the same distance away from their respective rings then you move on to the next check.....

Next step involves doing a continuity check of each sensor.
Trace the sensor wire back from the hub until you find a plug/socket. Unplug the sensor and stick the multimeter on the exposed pins (of the cable going back to the sensor). If you get an open circuit reading, then that sensor is fooked.
If all sensors check out ok, then I suggest your last resort is the ABS ecu (thats when you start crying).....

Good luck!

[Knight Rider S4]

One more thing is check the ABS relay under the steering wheel...has a 10A fuse in it ,,,and if it blows ..you know the rest

[spink]

another possibility is that the sensor ring has disintegrated,i had this recently.New cv joint needed of course.

[ujimaflip]

Thanks for all your input guys

I'll probably start with the easiest first - the fuse. Will update this thread when I have the answer (which may be a little while...)

Cheers

[ujimaflip]

Hurrah the ABS light is Out!!

. It was the fuse in the relay under the steering wheel! A pita to get to but a damn site less work than getting all the wheels off.

This forum is great isn't it? - nice one Knight Rider S4!

20vQC - hope yours is as simple!

I'll take it for a few brake tests later - still a bit strange that leaving the car blew the fuse - or maybe it was when I changed the battery....

Cheers

[Acidburn]

One more thing is check the ABS relay under the steering wheel...has a 10A fuse in it ,,,and if it blows ..you know the rest

i agree - taken from 20v.org

ABS Light ALWAYS ON
(J Tomislav)
Simple Check for it is the following

1. Remove footwell cover (driver's side ... this is actually the whole shelf).
2. Remove ABS relay (should be middle row all the way to left and it has a red fuse in it which is 10 amp I believe).
3. Look at fuse ... is it blown? If so, then here is your problem. Don't bother replacing fuse ... it will blow again. Replace the relay. If you still don't believe me, go ahead and put in another fuse and I bet it too will blow. This will prove the relay is toast.

The relay is found on all the 1990 - 1992 audi 90's and coupes ... regardless of drivetrain. Best way to make sure is to look at the part number on relay.
What happens is that there is this mother-of-a-diode inside that I can only assume shorts out over time. This diode is put there to 'absorb', if you will, any counter-EMF that occurs from turning off the ABS pump, so that the rest of the car's electronics doesn't go berserk.

[ujimaflip]

I guess I can expect the fuse to blow again then....

Oh well - I've already replaced the fuse - seems ok for the time being. If it goes again, I know what I need to do.

[mcandmar]

This forum rocks, i spent an hour testing sensors and faffing about, spent a minute searching the forum and its fixed. Never in a million years would i have found that fuse

[TurboTransAm]

My 1992 urs4 just failed its MOT on the abs light being on. I'm going through some checks now. Could someone tell me where fuse 31 is located please. I've removed the tray under the steering wheel (its left hand drive) and there's a mass of wires going into un-numbered sockets, and I've located the fusebox under the bonnet just above the firewall. There seem to be relays in there. The back seat is out. Is there anywhere I've missed. A shove in the right direction would be greatly appreciated. Thanks.

[mcandmar]

Open the drivers door and remove the panel on the end of the dashboard. Relay is number 4 in the fusebox under the bonnet.

[TurboTransAm]

Thanks - I'm on it...