EK

I have recently bought a 1989 C4. My anti-lock brake warning light intermittanlty comes on after driving 10 to 20 miles (about 50% of the time). The light does not come on when I start the car. When the light does come on, I can "lock" the wheels by braking very hard. Restarting the car resets the system and then the ABS works just fine (until I drive another 10 to 20 miles).

Is this more likely to be a ABS computer problem (possibly a wire connection) or a wheel sensor problem. I'll probably bring the car to the dealer next week. Thanks.

DaveK

Probably a wheel speed sensor - hammer should confirm where the fault is. But it's also worth cleaning out your accelerometers - that caused problems with my ABS (for 18 months before it was finally found) and some other people have had the same problem.

Andy Roe

It could also be something as simple as low brake fluid, but this normally produces the brake pressure warning light to come on too (unless someones removed the bulb...)

garrett376

As Andy mentions, be sure to check that all your warning lights come on when the ignition is turned on. It may be that the PDAS warning light is also on... in that case you've got more trouble shooting to do.

EK

My PDAS light does not come on at start up. Maybe its a bad ABS/PDAS computer.

Andy Roe

That should come on when you turn the ignition on without the engine running - replace the bulb! When you say that you can lock the wheels when braking, for how long? Does it feel like the traction control is kicking in at all? You should be able to feel the pulses in the brake pedal.

garrett376

I bet your longitudinal accelerometer has stuck but since your PDAS light is not working, you can't tell! Get that light bulb replaced, then investigate your accelerometers!

EK

When I say that I can lock the wheels, I mean to say that the ABS is not working. The wheels completely lock and the car skids until I release the brakes or the car stops.

I should clarify the PDAS light issue. When I start the car, half the time the PDAS and brake light illuminate for 10-20 seconds, and half the time they do not illuminate. The ABS light never illuminates on start up.

I would imagine that with a wheel sensor problem, the ABS should illuminate on start up every time. Is that right?