Hello

I have noticed that the anti-lock braking is engaging more and more. No matter what conditions are and on dry roards also. It seems when i first start vehicle and with in the first few brake applications you can hear it ( a tick tick also) along with pedal doing what it is suppose to. The problem sometimes when engages almost get rear ended. Is there a leak in the booster or a rest that can be done? any help would be greatly appreciated. I have a feeling this is an expensive problem. I hope I explained properly

i don't know if getting new tires had an effect on this , but started right after they were installed:confused:

Does the ABS light come on when the ignition is first turned on? Does it go off after a couple of seconds? Does it come back on when you move the vehicle a few feet? Is the ABS light on while driving?

I have a 2000 Safari with 139k AWD and I just installed 4 new tires and am having the same prob. ABS light comes on at start up for a few seconds and then goes off. It doesn't come on while driving. Please help before I drive through my garage door cause brakes give out when anti-lock kicks on. I also hear a ticking noise.

Hello

I have not taken it in yet and nobody seems to have a theroy before so I have something to discuss. It is exactly how you explained it with yoiur Safari. Scary as heck to. My garage door was within inches of me also. I was told maybe a sensor on one of the axles. I have the right rear that still sticks after the flush nd new gear lube was put in an maybe when it does that it sends a messages to the booster or other sensors??? but it is always in a straight line no matter if hot out cold rainy...and no indication it just happens. Well between the 2 of us we can share what we find out and have fixed unlesss some one out there can help

thanks
usa-1

Here is a GM TSB that might help both of you.

Brakes - Low Speed (Below 5 MPH) ABS Activation

Bulletin No.: 02-05-25-006B

Date: January 05, 2006

TECHNICAL
Subject:
Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface) Models:
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

Supercede:

This bulletin is being revised to update the correction and warranty information. Please discard Corporate Bulletin Number 02-05-25-006A (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 wheel speed sensor mounting surface using a wire brush, sand paper, emery cloth, ScotchBrite(TM) or other suitable material. Be sure to thoroughly clean the wheel speed sensor surface. There should be no rust or corrosion.
8. 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.
9. 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 (Canadian P/N 89022218).
10. 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 0-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344 (Canadian P/N 993037).
11. 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.
12. Install the rotor, the caliper and the wheel.
13. 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.

Thank you. This worked. I cleaned off the ABS sensors and mounting surface and the problem is gone. It cost me $0. This is the kind of fix I like. I don't know what I would do without this forum. Thanks for the reply old_master.

You're welcome, glad to help.