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Discussion Starter · #1 ·
Hi all
I was just wondering if there was a simple way to test ABS sensors to see which one has failed? For instance, does the sensor's resistance change when it fails?

BTW, my symptoms are.... the ABS light comes on sometimes while driving. Usually once on it stays on. Occasionally it goes off again. It's coming on doesn't seem to coincide with me actually using the brakes. Sometimes while braking at low speed I can feel the ABS working even though the wheels definitely haven't locked up.

Cheers
Kev
 

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Kevster,

I had a similar problem with my '92 9000. It turned out to be a build up of gunge on the face of the sensor. Provided you can get it out without destroying it ( 1 10mm bolt and some WD40 ) it is just a case of wiping it away. I seem to remember cleaning up the toothed wheel on the hub at the same time. Mine used to come on if I went through a big puddle and if you used the brakes before the water all drained away it assumed that the wheel had stopped and did the full ABS bit.

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How did you get to the toothed wheel? I have exactly the same intermittent problems with my ABS light and it's driving me crazy. I've cleaned the sensors, replaced the main and system relays and the da**ed light STLL comes on seemingly at random.
 

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I had a similar problem with mine. Right before the MOT and of course the garage failed it because of the light coming on. Anyway, it turned out to be water in the ABS ECU. So I dried it out overnight in the house and hey presto no more problems.
 

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Discussion Starter · #9 ·
Originally posted by Paul @ Kippen:
[qb]Kevster,
   
I had a similar problem with my '92 9000.  It turned out to be a build up of gunge on the face of the sensor.  Provided you can get it out without destroying it ( 1 10mm bolt and some WD40 ) it is just a case of wiping it away.  I seem to remember cleaning up the toothed wheel on the hub at the same time.  Mine used to come on if I went through a big puddle and if you used the brakes before the water all drained away it assumed that the wheel had stopped and did the full ABS bit.

[email protected] [/qb][/b]
I've cleaned up the front sensors and toothed wheels while fitting new wheel bearings, so it's not them. Could be the rear ones, or maybe a duff sensor.

How have people identified duff sensors in the past then? Do you just buy an new one and start fitting it in place of each sensor until the problem goes away?
Kev
 

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Kevster,
I had a problematic ABS light coming off and on a while back on my CS Carlsson. The only way I could definitely identify which wheel sensor was at fault, was be getting my local dealership to hook the car up to a Tech 2 diagnostic meter. This identified the rear n/s wheel sensor as the faulty one.
Hope that helps
DeeVee
 

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My local dealer sells more nearside front sensors than all the others combined. However, an attack of the diagnostics is the only sure way to find out. They are too expensive to replace speculatively.
 

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Discussion Starter · #12 ·
It may have to be a trip out to a mechanic with the 'puter then. I wouldn't mind betting though that it would be possible with a volt/resistance meter and an assitant to turn the wheels.
 

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The ABS ECU should be on the left hand side, below the windscreen and under the large plastic cover over the bulkhead in the engine bay. I think this area is prone to water build up so make sure the drain is clear. At least it was on our 1993 CDE.
 

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n/s front abs sensor most prone to failure due to hardest lifestile, with kerbing shocks and gutter potholes, and the collective gunk (sprayed up by the front wheel) from this part of the road.

Best to do diagnostic/SAT test though.
 

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It may have to be a trip out to a mechanic with the 'puter then. I wouldn't mind betting though that it would be possible with a volt/resistance meter and an assitant to turn the wheels.[/b]
I had an ABS sensor fail once and like yours it was intermittent which made me think it was more likely to be a connection problem or a faulty cable. I tracked it down by firstly, connecting a meter on ohms range across each sensor in turn and measuring the resistance - they were all about 900 ohms or so. I then did the same again but this time pulled and twisted at the cable from the sensor. When I tried the front nearside one the resistance varied as I pulled the cable. I'd found it.
It turned out that water had managed to penetrate the outer sheath of the cable (must have been a nick in it) and the copper screen was almost corroded away at the lowest point. I managed to successfully repair the cable which was still working more than a year later when I sold the car.
 

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Discussion Starter · #18 ·
Originally posted by Derek:
[qb] QUOTE
It may have to be a trip out to a mechanic with the 'puter then. I wouldn't mind betting though that it would be possible with a volt/resistance meter and an assitant to turn the wheels.[/b]
I had an ABS sensor fail once and like yours it was intermittent which made me think it was more likely to be a connection problem or a faulty cable. I tracked it down by firstly, connecting a meter on ohms range across each sensor in turn and measuring the resistance - they were all about 900 ohms or so. I then did the same again but this time pulled and twisted at the cable from the sensor. When I tried the front nearside one the resistance varied as I pulled the cable. I'd found it.
It turned out that water had managed to penetrate the outer sheath of the cable (must have been a nick in it) and the copper screen was almost corroded away at the lowest point. I managed to successfully repair the cable which was still working more than a year later when I sold the car. [/qb][/b][/quote]I have some tugging and probing to do this weekend then
 
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