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kensom

GM truck antilock brake issue

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I have a 2001 Tahoe & brother-in-law has 99 GMC truck, both had anti-lock turn on and stay on during normal driving. Only way to stop was to pull fuse....any ideas?

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Rust and/or corrosion under front wheel speed sensors can cause this. There may have been a TSB for this if I remember. I just did a 99 with this problem last Thursday! Basically the sensors have to be removed, clean the mating surfaces, apply anti-corrosion sealer and reinstall. No parts needed if this is the problem.

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Thanks Macgyver, I will give it a try, sounds like a logical solution.

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Here's the TSB referred to:

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

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.

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