ABS activation when almost stopped? 2003 Vue V6 AWD

[conefree]

Hey all,

so I finally figured out which ABS sensor was giving me difficulties, and replaced the rear driver side wheel bearing which was going as well. So I now have a quiet ride and working ABS to boot. However, now when I have almost come to a complete stop, I get an ABS activation until the wheels come to a complete stop (say from 5 mph to 0). My ABS system has had various difficulties over the last couple years and hasn't been active all that much. Is this a learning process now that the system has finally been reactivated, or something else I should be looking into? Thanks in advance.

2003 Vue V6 AWD 117k miles.

[fdryer]

There is no learning with ABS. It either works or not. Nothing in-between because of the inherent accuracy in design. In other words, if the ABS computer cannot pass its own internal self test every time the engine is started and the car is driven, ABS will disable itself automatically (and turn ON the ABS indicator) rather than risk causing any braking issue. The ABS/TC feature is always an enhancement to braking so if there's any failure then it disables itself and allows normal braking as it was always was - locking up any wheel when panic stops and/or rough roads allows wheel lock up to occur before ABS was invented.

What seems to occur from some posts are slow speed ABS activation that's tied to worn wheel bearings vibrating just right and causing ABS activation while cruising parking lots. This can still be another worn wheel bearing.........

[1QUICKBOLT]

Im having the same thing with my 04 RLawd . I had an abs light, ended up being the pass front sensor. Replaced it and light when away and bam started having abs issue's when coming to a complete stop. This car is starting to get on my nerves.

[TheVue]

The Saturn is not listed in this technical service bulletin but this may help.

I had this problem on my Suburban. Cleaning the surfaces solved the problem.
__________________________________________________
Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface) #03-05-25-007 - (09/29/2003)
Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface)
2002-2004 Cadillac Escalade, Escalade EXT

2003-2004 Cadillac Escalade ESV

1999-2004 Chevrolet Silverado

2001-2004 Chevrolet Suburban, Tahoe

2002-2004 Chevrolet Avalanche

2003-2004 Chevrolet Express

1999-2004 GMC Sierra

2001-2004 GMC Yukon, Yukon XL

2003-2004 GMC Savana

2003-2004 HUMMER H2

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 (SI Document ID #899664).
Disconnect both the front wheel speed sensor (WSS) connectors at the frame and harness.
Place a Digital Volt Meter (DVM) across the terminals of each WSS 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 WSS bore in order to prevent debris from falling into the hub during service.
Clean the WSS mounting surface on the hub to remove any rust or corrosion using a wire brush, or equivalent.

Important
Make sure that the sensor sits flat on the hub. Check the sensor flange against a straight edge to ensure flatness. If the sensor flange is distorted, replace the sensor.


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.
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.

[conefree]

Thanks for the ideas, everybody. I will first attempt checking/cleaning the abs sensors. Although, now that I have driven the car for a day, I have noticed that since I replaced the noisy rear driver side bearing, it appears to have been masking another bearing that is not as far gone. It is most noticeable at 65+ mph, and I can feel it in the steering wheel when turning right. This would point now to the front driver side bearing, correct?

Quite possibly this bearing has a slight wobble at low speeds that is causing the ABS activation, or I have a dirty sensor and just another bad bearing

More to come when I can afford dropping another $150 on a bearing....

[far2grumpy]

conefree ... see following service manual extract, which confirms your suspicion of which bearing is wearing - applies to noise but I suspect also relates to steering wheel vibration.

Important: A noise heard during left turns is a good indicator of a noisy right wheel bearing. A noise heard during right turns is a good indicator of a noisy left wheel bearing.

I'd be surprised if the ABS anomaly is related to wheel bearing. The majority of posts seem to indicate one of the wheel speed sensors (WSS) has failed - or nearly so.

The service manual lists two ways to test WSS:

1) Disconnect WSS electrical connector - use DMM to check for resistance through the sensor. Any value in range of 800-1700 ohms is OK.

2) Configure DMM to measure low-level AC voltage - connect to WSS connector. Give the wheel a good spin. AC voltage should (temporarily) exceed 100 millivolts.

The service manual includes complete instructions to test and replace WSS (and bearings) so repost if you'd like to review.

[conefree]

Update:

Thanks for the ideas and replies, everybody The second (front driver's side) wheel bearing was replaced a few days ago. The ABS activation at 5 mph persisted after having 2 new sensors in the system.

Last night I took off the other two wheels to inspect their sensors. Long story short, the front passenger side sensor had built up a layer of crud underneath it, forcing it up away from the hub slightly. So after cleaning the sensor and removing the crud/rust from the sensor mounting surface, my ABS now functions properly. Thanks again!

[Boodog]

I am responding to an old post to add a little data to the issue for future reference.
I developed the same problem on my 1997 SC2 today after I had replaced the right front hub and bearing: no ABS fault light but ABS activation when braking to less than 15 mph, such as coming to a stop sign.
It ended up being the ABS sensor on the right front side being out of alignment. The plastic peg on the sensor that keeps it in place had snapped off allowing the sensor to move out of place enough to cause the problem but not enough to be readily noticed.

[ProDriver77]

Had this issue all the time with a fleet of Chevrolet Express vans that I managed.

Wheel Speed Sensors would be replaced constantly and repeatedly, until finally a dealer had enough sense to check the wheel bearings.

Seems to be an issue with a wheel bearing component that when it wears out, starts tearing up the Wheel Speed/ABS sensors.

[talonsaab]

Its often a better deal/value and idea to replace the entire hub and ABS sensor together. Only issue is that front hubs are insanly difficult to remove due to galvanic corrision between the aluminum knuckle and steel hub/bearing. The rears are fairly easy. Vue's go through front wheel bearings like candy so best invest in a good one.