The story so far. I recently got a ABS warning light come on (96 x300 4.0 litre Sovereign). Perfect timing as it was just before my annual NCT/MOT inspection! The light comes on with ignition switched on, and stays on constantly.

Anyway, first I removed and cleaned the wheel sensors. One of the rear sensors refused to come out and so it was eventually "extracted" by foul means and replaced with one from my donor car.(97 x300 3.2 litre Sovereign). The replacement sensor was a little different from the original, being a black plastic body as opposed to the original metal one and it bolted on, in a slightly different orientation. Still the problem persisted. One of the front sensors had the earth cable broken off at the earth point on the suspension strut, so I repaired this and also renewed same on the other front wheel, just to be sure. I notice there are no such "extra" earth straps on the rears, is this correct?

Next I removed the ABS module and resoldered the dry joints, but still no change.

Then I replaced the ABS module with the one from my donor car and when I switched on the ignition the ABS light went out with all the other warning lights and stayed out when I ran the engine.

However, when I drove the car and got up to the 30mph mark, the light came back on, indicating that one (or more) of the sensors was doing it's job? During my various forays into this problem I also did regular hard resets and also tested the sensors and got back the correct readings. I also checked and cleaned all pins etc. at the main connector, the pump connector and at the abs connectors, front and rear.

My cruise control works fine, which is not supposed to be the case with an ABS failure, so any thoughts?

I now have a constant ABS light on, just as it was in the beginning, so does this need to be cleared, if the problem is sorted? The brakes feel and operate just as they always have, with no discernible change. I have also drawn off some brake fluid and/or topped up the brake fluid, as per some posts. I also tightened up a front wheel bearing, as I was advised of a slight play in same by the tester. He suggested that the play in the bearing might have been the cause of the ABS light.

How do I check that the actual ABS pump is operating?

Many thanks in advance for an issue that I have to get sorted asap as a retest is imminent. Can the light be simply cleared now, or what else am I missing?

 

Perseverence can always overcome good judgement! I would give serious consideration to getting the C-codes read so you know for sure what is happenning. You clearly have way more patience thatn me.

 

You've covered a lot of ground.

My ABS experience is limited so I can't answer your questions. However, I'll just throw out the idea of a loose reluctor wheel. When I had a weird ABS issue that was the problem.

You can easily check for this by removing the sensor at each hub and using a screwdriver thru the hole to determine if the reluctor is loose

Others will chime in will more/better advice, I'm sure.

Cheers
DD

 

I bought my car to a local mechanic today, to get the headlamp beam adjusted and asked him to run a diagnostics on my abs issue. It came back with two items. One was a abs pump motor failure ( or something like that) which was something historical, insofar as he cleared it. Possibly an issue related to my old abs module, pre change. He also got a rear right hand side wheel sensor fault!

So, drove the car and the abs light returned, which pretty much confirms things for me. Alongside that, this was the very sensor that I replaced from my donor car, having "butchered" the original one upon it's removal. The very one that is slightly different from the original, so, maybe the problem is solved. Just have to get an authentic "match" now and fit it. Fingers crossed!

Looked online and saw the sensors, from two different suppliers, one at £186 sterling and the other at £56 sterling! What's the difference?

 

Great!
It sure is good to have a donor car isn't it?

BTW, the motor fault is the indication (usually) that the motor connector needs to be re-flowed with solder. See the archives if you do not know about that.