ABS - 4wd nexus

[Darylbing]

I have had an ongoing issue with my four wheel drive trying to engage while accelerating. I tried a few things to troubleshoot, and the one thing that worked was disconnecting the front wheel speed sensors. I didnt have an abs light before, indicating a failure, but do now (understandably), however, my 4wd no longer tries to engage when accelerating. This is an advancetrac adding to the complexity. Any thoughts...please advise

 

[drdoom]

I feel from your description that you have already found the problem. Any service history of the front hubs available? I am also thinking you could get a live data stream, watching those sensors and of course the 4WD engagement.

 

[Darylbing]

I tested both front sensors and both are 15-16 ohms. Both are also polar, which I wasn't expecting, but the results were the same and neither were grounded. Will a dirty sensor test ok, but still fail? I havent tested the rear yet but will.

 

[Darylbing]

What sends the signal to engage the hubs? Is it vacuum?

 

[rrgone]

Any codes? Best to check with the front wheel speed sensors connected.

 

[Darylbing]

I feel from your description that you have already found the problem. Any service history of the front hubs available? I am also thinking you could get a live data streauhm, watching those sensors and of

Any codes? Best to check with the front wheel speed sensors connected.

Nope. No codes. I did just buy a Bosch 1050 to try and read the wss,but couldnt find the data on the bosch. I plugged the sensors back in and drove it to town and again, the 4wd was engaging as it was before. Unplugged the wss for the ride home, no 4wd engagement, but the abs warning came back on. The engagement is momentary, little more than a thumping when accelerating. When I drove it during winter in 4wd, the thump doesnt happen.

 

[rrgone]

Tires that are slightly mismatched can cause the auto 4x4 system to activate during some driving maneuvers. Have heard of this occurring during acceleration, coasting at speed, cornering, going uphill...

Worn bearings in a front hub can also cause this, as well as a failed sensor or it's cabling. What's the mileage? Any front bearing noise? Checked for wheel wobble with front end lifted?