I noticed today that the AWD is not working in my '03 Yukon Denali. I was attempting to pull into my garage on a slight incline and had the front wheels both inside the garage but at least one rear wheel was on an icy patch and it just spun without moving the vehicle forward. It is my understanding that the AWD setup in my Yukon should have been able to pull the vehicle forward with just the front wheels having traction.

My vehicle shows the RPO code NR3 which indicates it has the Borg Warner 4481 transfer case which is supposed to be full time AWD delivering 60% to the rear and 40% to the front at all times and using the wheel speed sensors to detect loss of traction and then employ braking on the spinning wheel in order to divert power to the wheels with traction. That's obviously not happening.

Does anyone know if this could be as simple as a bad wheel speed sensor? I had replaced both front wheel speed sensors a year or two ago due to the ABS system engaging when not needed and that fixed the problem, but now I'm wondering if my current problem might indicate a need to replace the rear wheel speed sensors?

Unless I find evidence that it's something else I'll just replace them, but since that's about $150 in parts I'd like at least some idea if there's a chance that will fix it.

I've been researching and have found some conflicting information, and no real consensus.

 

a mechanic with a high end diagnostic tool should be able to tell you if the sensors are misreporting, or if the ABS ecu has faults.

 

Thanks for your input but I'm trying to avoid putting it in the shop as the diagnostic charge would probably be pretty high and I'd still need to buy the parts to fix it.

It's an old vehicle though in very good shape. If it's going to be 2WD from now on, so be it. Unless I see a compelling reason to think it's something else I'll just replace the wheel sensors and see if that helps. It wouldn't be the first time I threw away $150, but if it goes in the shop I know how quick the bill can get into the thousands of dollars.

I'm trying to get as much information as I can now and won't decide what to do right away as it's not urgent in my eyes.

 

Might be a good idea to do a little homework regarding what wheel speed sensors do before spending a lot of $$$ that will not correct the problem.

 

You would rather throw away hundreds of dollars on sensors that might not fix the problem, rather than pay a $100 diagnostic charge. Makes perfect sense.

 

I have indeed done some research and unless you are telling me that the information I quoted below is incorrect, then I would say that perhaps you don't understand how wheel speed sensors interact with the ABS system in AWD vehicles.

It's possible the problem lies elsewhere but if it is the wheel speed sensors then replacing them should correct the problem.

It's a gamble either way. If I spend $150 on wheel sensors and that's not the problem then I lose the $150. If it does fix it I'm done at $150.

If I spend $100 for diagnostics and then find it's the wheel sensors I still have to spend the $150 for them and I'm in for $250. If I spend the $100 for diagnostics and it's something much more expensive I'm not going to fix it at all so I lose the $100.

Makes sense to me. Might not to anyone else.

 

the tranfer case control module will set dtc and these will be chassis codes as are abs codes.
the abs applies the brake on one axle to drive the opposing axle ie the other side...not opposing front or rear...applying the brake stops the diff from walking...the other end ie front should still be turning at least on wheel.
replacing all the wheel speed sensor is a shot in the dark. Can;t some place like autozone read the chassis codes for free. that is a good starting point vs guessing.

 

If you are gonna do your own repairs you need a scan tool before hand tools now days. No scan for codes then your just pis--ng into the wind hoping not to get wet.

 

What mechanism is used to control power distribution between the front and rear? Is this explanation entirely incorrect?





The way I read that there is no clutch pack or locking mechanism within my transfer case and it acts like an open differential. In which case without using wheel specific braking how is power sent to the front wheels when the rear wheels are spinning?


I'm finally starting to see that. I grew up on much simpler cars and don't quite grasp all the electronics used now. Give me a carburetor and a 4 speed manual and I'm happy.

At any rate my son is a VW auto tech and I thought scan tools were pretty much vehicle specific, but says he can scan my Yukon for codes so I'll see what happens with that later today or tomorrow and post up the results.

 

I m not taking about the torque split in the tcase. i am referring to the differentials. open diffs will spin one wheel...locking one wheel with the brake performs a function similar to a locking diff. that is what service info is referring to with abs interaction for the awd system.