GMC Sierra & ABS system: Troubleshooting help, please
Question:
– Hide quoted text — Show quoted text – >I have recently purchased a used 1996 GMC Sierra K1500 with a 350 Hp >engine, ABS. It has about 72,000 miles on it. >Regardless how little pressure I put on the brake pedal, just before >the pedal reaches its limit the pedal pulsates a bit and then there is >a reverse movement of the pedal along with strong resistance for the >pedal to be depressed. There is also a rather loud noise from the >driver’s side of the engine compartment. >It is as though the ABS has kicked on or is checking itself. >I would expect no noise from braking the vehicle. I would also expect >the ABS to be triggered only when the brakes are applied quickly and >firmly and with respect to the road surface. >Any ideas? Is this a defective ABS unit? Air in the brake lines? >Bad sensors? Bad or broken wiring or connectors? >Your sage counsel would be appreciated. Thanks.
Don’t know how sage I feel at 4am, but here goes. 
I have seen cases of vehicles where the back brakes are adjusted too tight causing the ABS to kick in. Another possibility is a leaking rear wheel seal or wheel cylinder getting oil or brake fluid or the rear brakes causing them to grab. The ABS would interpute this as wheel slip and kick in. Big Daddy ICQ#6342575 AOLinst messenger "WallyC1951" ASE Master Auto Technician Chevrolet Certified Master Tech.
Response:
I have recently purchased a used 1996 GMC Sierra K1500 with a 350 Hp engine, ABS. It has about 72,000 miles on it. Regardless how little pressure I put on the brake pedal, just before the pedal reaches its limit the pedal pulsates a bit and then there is a reverse movement of the pedal along with strong resistance for the pedal to be depressed. There is also a rather loud noise from the driver’s side of the engine compartment. It is as though the ABS has kicked on or is checking itself. I would expect no noise from braking the vehicle. I would also expect the ABS to be triggered only when the brakes are applied quickly and firmly and with respect to the road surface. Any ideas? Is this a defective ABS unit? Air in the brake lines? Bad sensors? Bad or broken wiring or connectors? Your sage counsel would be appreciated. Thanks.
