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Old 1st December 2020, 14:21   #1
rab60bit
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Default ABS warning light

Have to fix as MOT looming.
Checked all 4 positions using a new MGR sensor assembly plugged into each wheel circuit, light stayed on following each engine start-up/self test. It looks like a modulator fault so I have two options, fit a 'new' old modulator board or replace the whole modulator either way it's a pain in the bum.
If I replace the modulator assembly are there any particular issues (I presume the brake system will have to be bled so I might as well do a brake fluid change, one is due). A member on here recently replaced a modulator solenoid board and very kindly provided a how-to but has anyone got anything to add that could be helpful following either DIY route?
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Old 1st December 2020, 15:36   #2
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You may need to drive it before the light will go out. You need to find which sensor is faulty first.Try the search fuction.


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Old 1st December 2020, 18:35   #3
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It's tricky pinning down the fault, mine came on at slow speed right turns, it suggested crud or damaged bearing on the rear off side. Front wheel off and I saw insulation missing on the sensor cable (rubbing on wheel) Fixed that and light still on, so replaced the rear offside bearing. There was crud from a rusty backplate, did that and light popped on still. So I disconnected battery for 15 mins, reconnected and all is now fine. Now, it's been suggested that a battery disconnect does nothing to cure some electrical faults, I believe it works, a reset as it were.
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Old 1st December 2020, 18:38   #4
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Quote:
Originally Posted by Kev75 View Post
You may need to drive it before the light will go out. You need to find which sensor is faulty first.Try the search fuction.


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I thought there was a system self test each time the ignition is switched on?
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Old 1st December 2020, 20:54   #5
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Don't you hate the abs light.
One of mine was OSF . It was the wheel bearing . OSF usually accompanied by a faulty fuel gauge reading and a Speedo intermittent fail.
One was nsr . Corrosion on back plate . The sensor was fine
And correctly said they won't turn off until you drive the car after fixing the issue..
Although you will be better at diagnosis by the time you find the fault . keep it simple at first when you are looking for fault's
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Old 3rd January 2021, 21:03   #6
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Thought I'd post an update, it might help others.
Unfortunately it's not a true 'fix', rather just a fortuitous bit of delving about. I'd given the front and rear brakes a refurb. (new discs/pads and a good clean up around the backplates, handbrake pins/springs) two years ago.
I didn't want to have to spend +£40 and a 60 mile round trip on a T4 check unless necessary (I had a conversation with someone at Horners (my nearest T4) and frankly wasn't convinced they were going to be particularly helpful and as previously noted I thought I'd carried out a sensor system check on all four corners by plugging in a new sensor lead in order to eliminate any sensor fault; it was just a static check - some members commented that the car has to be driven some distance for this to be effective - but in any case the warning light didn't extinguish so my next thought was a reluctor ring. The car has done almost 170K on the original wheel bearings so the next cheapest/easiest option (for me) was a set of new rear wheel bearings (from DMGRS) - the front bearings are more difficult DIY job. It was an easy swap out (I had the right sized socket and my torque wrench maximum setting was exactly what Haynes listed) - might have been lucky but it was a breeze. I did the N/S first giving the sensor and surrounding area a good degreasing and clean up, dropped the car and went for a short drive round the block but the light remained illuminated - bu...r!
Repeated the same straight forward process for the O/S, quick drive round the block and...result, light extinguished and all's good with the world; a couple of days later she sailed through her MOT.
I understand that on our cars the ABS reluctor ring is built into the bearing grease shields. Apart from a small dent in the old wheel bearing shield (funnily there was a similar dent in both of the inner seals) the bearings appeared to be in top class condition (although the grease looked a bit lacking and a touch 'dry') but the balls and races were pristine.
Probably fitted new bearing ahead of a 'must do' but otherwise a good result.
Little tip - before fully torquing the wheel bearing flange nuts give the hub a bit of a hand spin when they are still just a little more than 'finger tight', it centralises the balls and races.
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Old 3rd January 2021, 22:18   #7
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Sometimes the fault code will need clearing before the light will go out.
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Old 4th January 2021, 11:43   #8
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Good result in the end, 9 times out of 10 it is always the rear OS bearing, at the same time check and clean the back plate, remove any flaking rust, treat and coat with some black paint, if to bad then change the back plates.

As stated T4 would help with finding out which bearing it is.
1

Front
1a

If you do not have access to one then a simple set up plugging in a new sensor may help.
2

3

Readings should be 1.72
4

Also 0.67
5

When turning the wheel while jacked up.

once you have found the problem which rear bearing it is as above check the back plate for corrosion and treat or replace.
6

7

8

you can see the corrosion flakes on this bearing.
9

If all this fails then look at the pins in the ABS modulator.
10

Glad you got sorted for the mot.
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Old 4th January 2021, 12:16   #9
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Thanks, I hadn't seen that how-to with the multimeter.
The backplates were a little bit rusty but nothing like so corroded as your picture - in fact that whole area was reasonably clean. The reluctor is obvious in your pic #10, my old/ replacement bearings are not like that at all although I did see some with the ring on the bearing housing on the web when I was looking around for replacements
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