Less than 20K km ago I replaced both front bearing hubs with Moog units on my 2005
One was growling and I figured the other was not far behind
On a recent camping trip just as I was about to leave I got a check engine light (bad O2) ... drove home towing the camper just sucking up fuel
I scanned when I got home and confirmed the O2
Just after I got back I started getting a ABS buzz just as I came to a complete stop no light on the dash
Its random ...I get from time to time ..Wife gets it just about every time she drives it
This morning I pulled the 60amp ABS fuse under the hood ..its put the ABS and (!)(P) lights on but not getting any ABS chatter now

I had the rear brake line replaced about a year ago and just prior to that the rear calipers ... everything was fine until now ...fluid is full

I run chunky mud tires so I will never hear another bearing going south now

 

You can check the sensors yourself with a multi-meter set to the mV-AC setting. Disconnect the WSS (wheel speed sensor) and connect the multi-meter to the two leads in the connector to the sensor. Spin the wheel. The mV-AC output should be around 300mV for a properly working WSS. Check both. If you don't have 300mv or more remove the speed sensor screw, clean the sensor real well as well as the mating surface, reinstall and measure your voltage

 

Burned hit the nail on the head! The root cause is an incorrect air gap on one of the front wheel speed sensors. Testing as he described will tell which side is bad. Don't replace just the sensor, replace the hub/bearing assembly.

 

does it have a rear sensor ?

 

Yes, it has one sensor that covers both rear wheels. It is commonly referred to as the VSS, (Vehicle Speed Sensor). 2WD it is located in the transmission tail housing, 4WD it is located in the transfer case tail housing.

 

Another thing I learned here. This is the first I've heard of the rear ABS speed sensor. Can that one also cause the "Under 5mph" ABS activation? What is the test procedure?

 

Nope, its the two front sensors causing the ABS to engage under 5mph due to the air gap causing erratic readings.

Read: http://ww2.justanswer.com/uploads/GM...s_bulletin.pdf

 

Vehicle speed and rear wheel loss of traction, are both monitored simultaneously with one sensor.


I suppose it could cause a low speed ABS activation however, the sensor is mounted in an aluminum housing, not cast iron like the front hubs, so rust is not an issue. Low speed activation is caused by rust pushing the sensor outward which increases the air gap.

 

I am curious, why would you replace the entire hub and not just the sensor?

 

Air gap is critical for the sensor, and not all hub/bearings and sensors are exactly the same. When the hub/bearing is originally assembled at the factory, the sensor is installed with shims if/as necessary. If you replace the sensor, you run the risk of destroying it due to nonexistent air gap, or the sensor not generating a signal due to excess air gap.