ABS again

[INTERCEPTOR]

My 97 9000 Aero is driving me mad.

My ABS light comes on at 20mph. I have replaced all the sensors at vast expense and I have replaced the ECU with known good item but still no change.

When my car went on a rolling road the light stayed off so it must be the rear wheels that are setting it off.

There is no play in the rear wheel bearing at all, the discs are running straight and I am getting to my wits end with it.

Has any body any idea what to try next?

The car passes its MOT OK because the light goes out after 3 or 4 seconds but it would be nice to get this fixed if possible.

My local independant does not have a Tech 2 so I am in the hands of the local Main dealer so any help would be gratefully received.

Steve

[paul anderson]

Steve,

I'm sure I've seem a thread about testing the wiring by sticking a meter across the connectors under the back seat and 'wiggling' the wiring about. The other thing that occurs to me is to check that the toothed wheels are not clogged up with 'crud'. This would give the sensor the impression that the wheel has stopped. I haven't done this job on the rear but I guess you would need to unbolt the caliper and strip the rear bearing to get at it.

Paul @ Kippen.

[INTERCEPTOR]

Hi Paul

Thankyou for the advice but I have already done that with the wires and toothed wheels. The toothed wheels are spotless and the wires show no fluctuation when wiggled even quite vigorously.

It is like something at 20mph clicks in activated by the rear wheels.

I have replaced the ABS ECU so I doubt it is that but are there any relays in the system that could cause this? There is one for the dash light as I can here it as the light goes out.

I once had a similar fault on an Omega several years ago and that turned out to be the brake light switch, I have changed that with no differance so it is not that.

Any advice will still be gratefully recieved.

Steve

[Mark B]

There are 2 relays in a little box to the rear of the battery. One is quite expensive, as I found out when my dealer's Tech 2 diagnosis proved to be incorrect. Sadly I can't remember what each does.

[tempdisplay]

I realise this is frustrating as I recently replaced the front nearside ABS sensor -knowing it to be the cause and failed the MOT because it was not the only point of failure in the ABS system.

In the usual style of decreasing circles and living in hope I now systematically service all the electrical connections as they are brought into the frame because oxidation and capacitance seem to wreak havoc with both dc and ac signals. I have an intermittant rear brake light monitor indication... odds are its a wiring connection where exhaust gases and condensation have tended to hang around.

Which reminds me to service all the rear end electrical fittings soon.

Cyclical maintenance can become a form of relaxation.

I hope you get this sorted without too much more trouble by the way.

[adrian]

My local dealer charged £35 a couple of years ago to read the fault codes on my ABS. I would always start their with ABS problems.

It is worth cleaning the two electrical connectors to the ABS pump and hydraulic lock unit.