ABS module problem??

[DPC]

06 LBZ has an odd braking issue. When the brakes are applied truck stops fine until just before you come to a stop. The steering wheel will see-saw back and forth like the front brakes are alternating back and forth.

System has been bled 3 times, truck has braided steel lines. Automated bleed with a scanner has also been performed. No codes, all wheel speed sensors reading correctly. No calipers hanging. The only thing that was slightly off is that the L/F caliper does not bleed as freely as the others. Thoughts... Thanks.

 

[gmduramax]

How’s the condition of the hubs?

 

[DPC]

How’s the condition of the hubs?

Hubs are good, no play or binding and spin freely.

 

[THEFERMANATOR]

There's a known issue where rust builds up between the hub and wheel speed sensors, and it opens the gap on them causing erratic speed readings at slow/parking lot speeds. Pull the sensor out, take a grinder with a roloc cleaning disc, clean the mounting surface of the hub back to shiny metal, and reinstall the sensors. You get erratic spikes in the speed sensor readings that are enough to trigger the abs, but not enough that shows up on a scanner, but you'll see it with an oscilloscope.

 

[DPC]

There's a known issue where rust builds up between the hub and wheel speed sensors, and it opens the gap on them causing erratic speed readings at slow/parking lot speeds. Pull the sensor out, take a grinder with a roloc cleaning disc, clean the mounting surface of the hub back to shiny metal, and reinstall the sensors. You get erratic spikes in the speed sensor readings that are enough to trigger the abs, but not enough that shows up on a scanner, but you'll see it with an oscilloscope.

Thanks, I'll give that a try.

 

[THEFERMANATOR]

Pretty common issue.

https://youtu.be/4fyjZB0gWIw

 

[DPC]

Pretty common issue.

https://youtu.be/4fyjZB0gWIw

Cleaned the hubs and no change. Unplug the ABS module and everything works like it should. We also noticed that the truck rolls or moves easier with the ABS unplugged, like the bakes were very slightly applied.

 

[Chevy1925]

ive had 3 trucks do what you have stated and they were all sensor related. non had the rust issue like Ferm is talking about (we dont get rust out there) BUT the sensors had been removed prior from the hub for various reason (one was a lift kit, other two were cv removal/replace), these were all trucks that came to me after work was done to them and the shop couldnt find the issue or fix it. the side that had the sensor removed had the wheel hub/sensor assembly replaced and the slow speed wobble issue went away. there have been a few other shops in town that have called me about that same problem and new assemblies fixed it. You get no codes, scanner wont see the problem, brake pedal does not vibrate like abs is activating, bleeding makes no difference, hubs all feel great. Just for what ever reason, something gets damaged or screwed up the moment the sensor comes out every once and a while on a hub assembly. i quit taking the sensors out because of the issues ive seen and been called about.

you might want to find a little more back history on that truck if you dont want to replace both sides but that was the only fix. its a very odd issue.

 

[DPC]

ive had 3 trucks do what you have stated and they were all sensor related. non had the rust issue like Ferm is talking about (we dont get rust out there) BUT the sensors had been removed prior from the hub for various reason (one was a lift kit, other two were cv removal/replace), these were all trucks that came to me after work was done to them and the shop couldnt find the issue or fix it. the side that had the sensor removed had the wheel hub/sensor assembly replaced and the slow speed wobble issue went away. there have been a few other shops in town that have called me about that same problem and new assemblies fixed it. You get no codes, scanner wont see the problem, brake pedal does not vibrate like abs is activating, bleeding makes no difference, hubs all feel great. Just for what ever reason, something gets damaged or screwed up the moment the sensor comes out every once and a while on a hub assembly. i quit taking the sensors out because of the issues ive seen and been called about.

you might want to find a little more back history on that truck if you dont want to replace both sides but that was the only fix. its a very odd issue.

I'll see what I can find out, thanks.

 

[DPC]

sensors

Update...Put two new GM wheel speed sensors in the front hubs and problem solved.

 

[Chevy1925]

Good to hear

 

[snowman22]

Update...Put two new GM wheel speed sensors in the front hubs and problem solved.

Thanks for the follow up, I'm currently fighting a similar, but different issue. This was divine intervention to make me buy the two rear sensors my cheap ass didn't want to do.