ABS problem

First thing, are they sure it's both front wheel speed sensors acting up? When I encounter this type of problem, it's almost always only one sensor causing the problem. There is also a bulletin about this problem, you can often solve the problem by removing the speed sensor from the hub and clean the mounting surface of any rust or dirt build-up between the sensor and hub. I'd start by doing this. All you need to do is pull the front callipers off, and remove the front rotors, very simple stuff. You will see the speed sensor after you get the front rotors off. (this is a 4x4 model, right?)

Ian

Here's the bulletin:

Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface) #02-05-25-006A - (Nov 26, 2002) Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface)

1999-2000 Cadillac Escalade 1995-1999 Chevrolet Silverado (Old Style) 1995-2000 Chevrolet Suburban, Tahoe (Old Style) 1995-2003 Chevrolet Astro Van, Blazer, S10 1995-1999 GMC Sierra (Old Style) 1995-2000 GMC Yukon, Yukon XL (Old Style) 1995-2001 GMC Envoy, Jimmy 1995-2003 GMC Safari Van, Sonoma 1995-2001 Oldsmobile Bravada

This bulletin is being revised to change model information. Please discard Corporate Bulletin Number 02-05-25-006 (Section 05 -- Brakes).

Condition Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.

Cause The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.

Correction Measure AC voltage and clean wheel speed sensor mounting surfaces.

1.. Raise the vehicle on a hoist. 2.. Disconnect both the front wheel speed sensor harness connectors. 3.. Place a DVM across the terminals of each sensor connector. 4.. Rotate the wheel with hand speed and measure the ACmV's. The reading should be at least 350 ACmV's. 5.. If the reading is between 200 and 350 ACmV's, remove the wheel, caliper and rotor in order to gain access to the speed sensor. 6.. Remove the wheel speed sensor and plug the hole to prevent debris from falling into the hub during service. 7.. Clean the speed sensor mounting surface on the hub to remove rust and corrosion.

Important Make sure that the sensor sits flat on the hub. If the sensor flange is distorted, replace the sensor.

8.. Apply a thin layer of bearing grease to the hub surface prior to sensor installation. 9.. Install either the original sensor or a new one in the hub and secure the sensor. Ensure that the sensor is seated flush against the hub. 10.. Install the rotor, the caliper and the wheel. 11.. Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel by hand. The voltage should now read at least 350 ACmV's.

Ian