ABS issues

[Knockenwelle]

I just got my project back on the road after 3 months of work. The only issue I'm having so far is with the ABS: 7 times out of 10, when I start the car and drive off, the ABS light will stay off. Upon braking, the ABS suddenly starts fighting me and causing wheel lockup and very uneven side-to-side braking. The other 3 times out of 10, the ABS light turns on the first time I hit about 10 mph, and the brake system works perfectly, but without ABS. All four wheel sensors and their sensor rings are in good condition. The car WAS completely apart, with no suspension or calipers attached for about 3 weeks. The brake pedal is high and solid. I'm thinking I may have an issue with air in the ABS hydraulic unit? Is there any way to pull "trouble" codes from the ABS computer? Thanks.

[jlevie]

Air in the ABS won't cause the problems you are seeing. It could cause a soft pedal or lack of ABS effectiveness, but not improper activation of the ABS. That condition results from a wheel speed sensor or ABS module problem. I don't think the ABS on these cars can be interrogated for codes, so diagnosis is going to be a matter of swapping in know good units. In this case I think I'd start with the ABS module, if the wheel speed sensors all ohm out to the same value. Otherwise replace the wheel speed sensors and go from there.

[Knockenwelle]

Thanks for the reply, Jim. That's some good info. I'll check the sensors out with my DVM. I don't remember how many pins each had; is it just two? The reason I'm suspecting air over sensor damage is that the ABS worked perfectly before I took the car apart, and I was careful to mark which wheel the sensors came from and to handle them carefully. But after 225k miles, who knows... Also, I had the axles off the car and switched then side-to-side when I rebuilt them, but I can't imagine they have different reluctor wheels?

[jlevie]

The sensors are two wire, as I recall. Swapping parts left to right should have no affect on the operation of the ABS.