ABS engaging randomly...HELP

[Lucky SOB]

Ok so I have this friend with a 2001 GMC Jimmy(or blazer...idk). V6 4wd. When the car is started the ABS light comes on. It sometimes goes off when the brakes are applied, sometimes not. On a cold start the ABS seems to engage when it is not nearly necessary. Sometimes this happens even after it is warmed up, but not as much. Please help! thanks in advance!

[jada64]

Sounds like a bad ABS sensor, those are expensive...

[phoenix_rising]

We had that happen in our '99 Jimmy. I believe it was a sensor or it could be an error. Try having the code cleared and see if it comes back.

[MP81]

ABS sucks...

[Lucky SOB]

i was thinkin the sensor also. but ya i agree. I'll tell em to get the code cleared or atleast read first.

[lozanoa11]

wheel speed sensor or abs computer

[MP81]

When did this start happening?

[Lucky SOB]

i think she said about a month ago...

[TSTONE]

its going to be an abs wheel hub speed sensor dropping out - the cheapest/easiest way around is to pull the abs fuse and defeat the system

youll no longer have abs (it act like conventional brakes) but itll stop false engagements too

but here is the info i have on it if you want to try and fix it:

2001 GMC Truck Jimmy - 4WD

Subject:Antilock Brake (ABS) Activation at Low Speeds (Clean Wheel Speed Sensor Mounting Surface) #02-05-25-006B - (01/05/2006)

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

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. Disconnect both the front wheel speed sensor harness connectors. Place a DVM across the terminals of each sensor connector. Rotate the wheel with hand speed and measure the ACmV's. The reading should be at least 350 ACmV's. 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. Remove the wheel speed sensor and plug the hole 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, ScotchBrite™, 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 (Canadian 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 (Canadian P/N 993037). 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. Install the rotor, the caliper and the wheel.
2. 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.

Parts Information

Part Number
Description
89022217
(Canadian P/N 89022218)
(Package of 2 cans)
Rust Penetrating Lubricant
(Each can will service 50+ vehicles)
01051344
(Canadian P/N 993037)
(Package of 12 tubs)
Wheel Bearing Lubrication - Tub
(Each tub will service 25+ vehicles)

Place unused material on dealer shelf for future use.
Warranty Information

For vehicles repaired under warranty, use:
Labor Operation
Description
Labor Time
H9714*
Front Wheel Speed Sensor Inspect and Clean (Both Sides)
1.2 hrs

[phoenix_rising]

I would try clearing the code first. Sometimes cars will throw errorenous codes that will go away once cleared. My bird was doing that but every time we looked at the problem there was nothing wrong. We cleared out the code and it has not come back so I am guessing it was just a fluke.

[TSTONE]

this is not going to be a code issue - a code will never cause an activatrion - this is a very common problem see above bulletin

[02RedCamaro]

I had this old problem with my old sonoma and now this s10 that I have now. Mine are really sensitive and engage on just about anything except for dry pavment. They engage when I hit little pot holes and it pisses me off cause it cuts the power to all of the brakes. I hate abs and I think i'm goin to pull the fuse here shortly.

[1BADAIR]

Abs systems do a self check at a set speed 18-25mph. The codes are not really clearable. remove the sensors and clean the surface. Seen it hundreds of times. Most times it happens while slowing to turn into a driveway and such.
s/t and c/k trucks are known for it

[Lucky SOB]

great. thanks for the help guys! pretty sure I'm gonna tell her to deal with it until spring cause I sure as hell ain't workin on a car in these temps.