At low speeds, 8mph to 0, under very light braking, the ABS system activates. There is no light on the dash. So i cleaned the wheel speed sensor mounting surfaces on the front wheels, that fixed the problem in a previous truck, but it didn't fix it this time. That makes me think that one or both of the sensors are going bad. I can't think of any other sensor that would cause what I am experiencing, the rear tire speed is monitored through the VSS in the tranny, and I don't think thats the problem.

Can someone explain how to test the wheel speed sensors, so I can figure out which one is going bad on me?

 

Not a problem friend....all you had to do was ask. Below is your testing instructions. I feel you may have a corroded reluctor ring.

This bulletin is being revised to add the 2007 Silverado/Sierra Classic models. Please discard Corporate Bulletin Number 03-05-25-007C (Section 05 -- Brakes).


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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 the wheel speed sensor mounting surfaces.

Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in the General Information sub-section of the Service Manual.
Disconnect both the front wheel speed sensor connectors at the frame and harness.
Place a Digital Volt Meter (DVM) across the terminals of each wheel speed sensor connector.
Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV's. If the reading is less than 350 ACmV's, remove the wheel speed sensor. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
Plug the wheel speed sensor bore in order to prevent debris from falling into the hub during service.
Clean the wheel speed sensor mounting surface using a wire brush, sand paper, emery cloth, scotch brite, or other suitable material. Be sure to thoroughly clean the wheel speed sensor surface. There should be no rust or corrosion.
Check the sensor head to determine if it has been warped/distorted due to the corrosion build up or other causes. Check the mounting surface on the sensor head for flatness by placing it on the edge of a metal machinists scale or other suitable straight edge to measure the flatness. Check the sensor for flatness in multiple (minimum 3) positions/directions. If the sensor head is distorted, replace the sensor.
Apply (spray) two thin coats of the specified rust penetrating lubricant (corrosion inhibitor) to the complete sensor mounting surface on the bearing hub. Allow to dry for 3-5 minutes between coats. Use ONLY Rust Penetrating Lubricant, P/N 89022217 (in Canada, P/N 89022218).
When the corrosion inhibitor is dry to the touch (about 10 minutes), apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344 (in Canada, P/N 993037).
Install either the original sensor or a new one in the hub. Ensure that the sensor is seated flush against the hub. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel. The voltage should now read at least 350 ACmV's.

 

Okay, I cleaned the surfaces last night, and got nothing. You mentioned a corroded reluctor wheel (effectively the wheel bearing, right)? How do I know if its the reluctor wheel or the sensor thats bad? I will measure voltage today and see which one is faulty, but that still wont tell me which part to replace, reluctor wheel or WSS.

 

AllData FTW

it could possibly be a chipped or missing tooth on the reluctor also right Torque Wrench?

 

If I may field this one for TW...sorry to answer a question directed at another but I know the answer...

Yes, a chipped or missing tooth will give a bad signal to the sensors and cause ABS issues such as pre-mature activation...

 

Okay, well, I went to Chevy, and they told me to eat **** because my truck isn't covered by the warranty. Then, on the way home, the ABS stopped activating at low speeds. I haven't tested the sensors yet, so I still don't know if thats a problem or not. Is it possible that the sensors just needed a few miles put on them after being cleaned to start reading wheel speed correctly? I did test drive it last night, but it was a short, 2 mile drive.

As for the broken tooth on the reluctor wheel...would I be able to see that through the wheel speed sensor hole if I pulled it apart and rotated the hub? On that note, I have AWD, will rotating the hub cause any issues in the front differential?

 

a cheap fix would be to unplug the abs fuse on side of dash. your brakes after this will work normal and no have issues besides a dash light. under 5mph the abs activates and is a common thing on older GMs. It was noted in a bulletin that this will cause an accident.

 

Thats not really a "fix". If I need the ABS to work, it will function properly, its that right now its doing it even when I don't need it to and its annoying. I read the bulletin, unfortunately GM feels that its not really happening because my year isn't covered. Maybe I should go out and slam into someone just so I can sue GM

 

you are correct its not a fix but is a way to stop from the abs malfunctioning. The GM abs system sucks without issues. Go over a bump it turns on and etc. Id much rather have non abs brakes then GM abs.

I was just giving you a simple way to deal with your issue for the current moment

 

I appreciate that. Do you know which fuse to pull, in case I decide to. Like I said earlier, its not happening now and hopefully it stays that way, but if it continues, I might just pull the fuse and say the hell with it.