oups59

I have the ABS warning that comes on as soon as I start the car so most likely cause is the ABS relay on the CE Panel. I bypass the relay by plugging two spade terminals into the slots on the relay board, that correspond to pins 30-87, no change.

So the next step is to change the 2 relays on the pump ??

StratfordShark

Not necessarily. When I had ABS light on ignition turned out to just be ABS fuse. I had moved the controller when working in footwell without disconnecting battery, so must have caused a spike when I plugged it back in. All fine with fuse replaced

Lizard928

Check the fuse, then test the two relays on the pump itself.

I just troubleshot one the other day where the pump motor has siezed.

oups59

I Forgot to mention that the fuse is good. This is the first things I did.

How do you test the relays on the pump?

Lizard928

Actuate out of the car of a battery using pins 85/86.

Asiandude

Just had this very problem on my '87 auto; relay and fuse checked out fine on the fuse panel, but warning light still on. Pulled the two relays on the ABS pump (they looked perfect even after 25 years) they also checked out fine, put them back and....all is well, no more warning light. Hope yours is as easy a fix.

oups59

After replacing the both relays on the pump, the abs warning light still on as soon as I start the car.

Next step is to check/replace the pump or the brain ? Can the pump or the brain can be repair? Or I need to change them ?

PorKen

If it happens as soon as you start the car, vs. after the system-check at 4 mph, then it is likely the ABS relay.

The relay has a big diode in it which goes bad. The relay is surprisingly expensive, BTW.
You may get lucky with a used one, but it may also go bad in short order.

Almost all of my S3s needed one when I bought the car, or soon after.

oups59

Already changed that relay and yes, it is expensive

oups59

Will a '91 ABS hydraulic unit 928.355.955.00 works on my '88 or I need to install the same unit 928.355.755.04 ?

mickster

Luc-could just be bad sensors at any of the 4 corners. Before jumping to the pump-you should check each hub. Also check the grounds on the front facing side of the battery compartment under the plastic cover. Those connect to the ABS and if there is a ground issue there, you'll get the warning.

123quattro

Bad wheel speed sensors most likely won't cause lights at key up, unless the wires are physically broken going to the sensor.

mickster

That would be my concern and first check along with a missing ground.

oups59

All ground points were cleaned .

John Speake

You have permanent 12v either side of the junction in that little black box near the ABS hydraulic in the engine bay ?