BrianG

The only thing currently stopping me from licensing my new GT is that ABS error message on the dash computer. They will not pass the import inspection with non-functioning OEM systems.

It sounds like it is going to take some time to get this ABS issue sorted so I need to temporarily kill that error message on the dash pod.

Any ideas?

NAvyC4S

pull the bulb?

BrianG

The '89+ cars have a central enunciator display that reads out the ABS failure, NOT just an idiot light.

Panzer9

Try replacing the one relay(of three) under the footboard. This is very likely the culprit- about $100.

IcemanG17

The easiest check is the fuse and relay on the main board.....

One way to narrow it down is this:

Is the light on all the time, or only once the car starts moving? If its once it starts moving then its a wheel sensor....anything else is a relay-fuse-brain problem....there are two relays on the pump too....the easiest way for you to pass is to find a known good ABS 928 and swap out parts until you figure out whats broken!

BrianG

Apparently relays were replaced by the PO.

The error message comes on after rolling, so it seems "sensor side" but I cannot determine how to test sensor function. John had a good idea for testing sensor integrity and I'll go with that, but that doesn't test for proper signal.

Mrmerlin

I think a spanner will test your system and tell you the correct wheels sensor thats bad, spanner connection is next to the passenger seat under the side cover that houses the amp

BrianG

Can anyone confirm the effect of unplugging the ABS brain, in terms of the central warning system indication on a '89+ car??

Would it result in a fault indication of the idiot light OR on the digital readout on the dash?

or would there simply be no ABS information displayed?

RichS 1986928

Not sure if it will help you with the 89 but on my 86, if you disconnect the wiring harness to
the pump inside the driver's front fender, the ABS light goes off for good.

jcb928

Any luck?

BrianG

Will get at the whole brake issue tommorow......... have the day off!

BrianG

Killing the ABS ERROR MESSAGE is easy..... just unplug all 4 of the ABS sensors at their wheel connection.

Since the ABS computer senses the "difference" in ABS signal frequency from each wheel, no signal from any wheel = no difference = no error message.

That's the easy part and it worked for my safety inspection. The Inspector stated that the ABS system is not considered "an integral part of the braking system" since it does not affect "normal braking operation" so it's not a "fail item" in the inspection. Bureaucrats!!

I devised a method of ascertaining individual wheel-sensor function that works, too.

With all wheel sensors disconnected, connect one sensor and roll the car 30-50 ft. If the sensor signal from the connected sensor is good, it gives the ABS computer enough wheel motion signal to determine that something is amiss, and it will set the error message (being as there is no signal coming from the other sensors). If you rotate each wheel sensor into connection while the others are disconnected, the dysfunctional one will not set an error message. Then it remains to find out what the issue is, between the sensor and the computer. It could be the sensor, or the wiring harness from the sensor to the computer.

This diagnostic procedure revealed that my left rear wheel sensor circuit was dysfunctional. Replacement of the the sensor with one of the working units will reveal if it is the sensor or the wiring.

Of course, with my luck, it turned out that the left rear was the 4th wheel tested..... but I guess I know that the rest are working. Now I hope I have better luck with the question of sensor vs wiring harness........

BrianG

Alright.......
I'm about ready to toss in the towel on this!

The above diagnostic procedure demonstrated a signal from every wheel reaches the ABS computer. Plug in all four sensors....... ERROR MESSAGE still appears.

WTF??

Has anyone here had an ABS computer go bad?

Mrmerlin

check the harness connections under the hood near the rear of the shock towers, chances are the wires are fouled up in or near the round barrels

BrianG

I checked the wire connections in the round barrels at the wheels and in the engine compartment. Nothing obvious at either............