ABS pulses at startup and when stopped?

[Red92]

So my '94 GT has a strange issue with the ABS... and although there are tons of threads on this and other message boards about ABS, none of them seem to be the same as my problem. :-\

 

 

When I start the car, with my foot on the brake pedal, the ABS pump will kick in a few times in short bursts in a somewhat random fashion, and then quit. After that, when driving the car, it will occasionally kick in again, but only when the car is stopped and with the brake pedal held down.

 

The ABS light on the dash is not on, and it does not come on when the system is acting up either, but it does light up with the ABS fuse pulled so I know that the light itself works. I tried to check for codes, but I couldn't find the controller? It's supposed to be under the front passenger seat, right?

 

 

For now, I have pulled the ABS fuse, and the car stops completely fine. But I would like to fix whatever is wrong.

 

 

The pedal moves down a bit when you first step on it, so I suspect the brakes might need a bleeding. Would air in the lines cause the ABS pump to cycle like this? Is the ABS activation triggered by how far down the pedal is?

 

Thanks

[Red92]

Also, I have read a lot about the ABS relay going bad. From what I can tell though, the car doesn't have those symptoms. The pump doesn't run when the car is off, and the battery isn't going flat when I leave it for a while.

 

I'm not sure that this completely rules out the relay though...

[Red92]

With some help from the folks at LegacyCentral, I found the ABS computer. But even after replacing the ABS fuse and letting the system act up again, there is still no dash light, and no codes blinking on the ABS computer. :-\

[nipper]

No codes and weirdness i would suspect a cracked tone ring.

[Fairtax4me]

Same thought. Check all the sensors and tone rings. Make sure they aren't full of metal shavings or some other kind of crud.

Beyond that, the ABS computer may be bad.

[Red92]

The tone rings are buried in the hubs, right?

 

Do I remember correctly that you have to pull the wheels and the brake rotors to be able to see them?

[nipper]

Yes but it is easy. Also a bad ABS sensor can do this too. Inspect the sensors, make sure they are perfect cylinders in hsape (no rounded edges). Rounded edges will throw off the magnetic pulse they are looking for.