2003 Chev Suburban AWD Troubleshooting
 

We have a 2003 Chevrolet Suburban that has AWD and the Stabilitrak system and 175k miles.

We get the occasional traction control warning when leaving stop signs, etc, turning traction control off makes that go away. Suspected wheel speed sensor that needs to be changed.

It developed a shake under power, doesn't happen when it is first started but after 10-15 miles. Felt like a CV joint or U joint.

It has the Borg-Warner 44-82 AWD Transfer case. Fluid is within 1/8in of full at the fill hole, fluid is clean.

It is currently on jack stands with all four corners in the air. The transfer case is supposed to split power constantly at 40/60 f/r.

When I put it in drive or reverse the rear wheels turn, fronts don't. The front driveshaft isn't turning.

When I switch to 4LO it turns traction control off and operates normally, front and rear wheels turn.

I switched back to AWD, turned the traction control off, front wheels turned briefly, then stopped.

With the truck off and in neutral I can turn the rear driveshaft by hand and the front does not turn.

The front driveshaft feels a bit like it is binding when turning by hand, it freely as the rear.

Thought? Internal transfer case issue? Stabilitrak issue (no dash/message center warnings, etc)? Switch issue?

There is an actuator motor on the rear of the transfer case housing.

TIA

Scan it for faults and start there.

I'll have to get my hands on a different scanner. None stored that an over-the-counter scanner can read - looks like I need one that can read ABS codes to get to Stabilitrak.

On a new note, I pulled the fuses today for ABS and the Stabilitrak systems. Turned the truck on, and got all the corresponding warnings and chimes, but no difference in symptoms.

I did switch to 4LO again, and the truck performed as intended. Went back to neutral, changed back to AWD, and into drive, the front wheels were turning, which was an improvement. I could brake and release the brake and they would turn.

As soon as I went to neutral or park and then back to drive, the front wheels wouldn't turn. Go back to 4LO, they would turn, switch back to AWD, shift from neutral to drive and they would turn. Shift to park or neutral and then back to drive.. nothing.

I had a 2001 Suburban back in 2010 and I recall there might have been a service bulletin about this. I will look at Alldata tomorrow.

Thanks. I'd appreciate that.

Picked up a new scanner - found the following:
ABS Codes:
C0035 Left Front Wheel Speed Sensor
C0050 Right Rear Wheel Speed Sensor
C0201 Open or Shorted Master Cylinder Pressure Sensor
C0110 Pump Motor Circuit Malfunction
C0244 EBCM Control Valve Circuit
C0240 EBCM Malfunction
C0196 Yaw Rate Malfunction
C0455 Steering Position Sensor Circuit

Then under OEM Enhanced PCM:
P1571 Traction Control Torque Request Circuit
P1689 Delivered Torque Circuit Fault

The transfer case RPO for reference is NR4 TRANSFER CASE ALL WHEEL DRIVE (AWD), OPEN DIFF, TWO SPEED

EBCTM on those things are a common failure point and presents itself in a number of ways and creates cascading issues.

Had them fail on my 01' and 05' Tahoes.

They sit on the outside of the frame rail under the driver door. Tend to get dirty and abused.

I've had it throw bad wheel speed sensor codes even with known good sensors because I just replaced the mofo's. One of them twice because I thought I got a defective unit.

Thanks! I was just reading about testing the EBCTM. The last two codes tie back to that control module, and it looks like some of the ABS faults do as well.

I was getting ABS faults with both bad EBCTM's.

The only TSB I found was related to the C0455 fault, a software re-program. I doubt it’s just that.

With so many faults I’d suspect a bad EBCTM as well.

There are a LOT of TSBs so I might’ve missed one…

Thanks Jeff and Scott. Another forum posted a link to a great resource for transfer case parts with exploded diagrams. This AWD transfer case has a Fork - Shift Range and a Fork-Mode Shift. I am wondering if there is something in the StabiliTrak, controlled by the EBCTM, that does something to the transfer case mode that changes the torque split between front and rear leading to the front shiftt not turning at times. All the docs I've come across say it is supposed to be a 40/60 split, and I am assuming continuous, but maybe it's not??

I had an 06 Tahoe and I had issues with the transfer case trying to engage 4wd while I was driving.
It was very intermittent.
It turned out to be an encoder ring in the transfer case motor. It was easy to change. Youtube really helped.
It may not be what your issue is but what you are describing reminded me of what I went through

i have an 01. 330k miles on it.
what a freaking TANK these things are.
whats funny is i getabout 14 mpg around town, i get 14mpg towing a heavy car trailor with car on hiway. i get 14 mpg if i baby it.
whats not funny is $100+ for a 30gal tank.

I heard back from Rockland Gear. I reached out to them as they had an archived document on the operation of the Borg-Warner 44-82. He indicated that the ABS-related codes could cause the transfer case behavior.

Sounds like that's the place to start - clean up the mounting surfaces for the wheel speed sensors, check their function, then most likely replace the EBCTM and see what happens.

Replace the wheel speed sensors, they are cheap enough and do get brittle over time.

Cleaning and inspecting is more work than replacing and if you do find one to be faulty you are going to want to have the replacement part on hand anyway.

My money is still on the EBCTM.

I agree, but the wheel speed sensors are easy to get to and check off the list. I have to admit, I'm worried about the back two screws on the EBCTM considering I am in the land of rust. The underside of the Suburban isn't too bad, but still, it's 19yrs old and has been exposed to sand and salt.

I was just suggesting that since checking them thoroughly requires removing them completely seems logical to just toss in new ones.

It's like doing a water pump when you do a timing belt, no additional labor and the peace of mind of one less thing to worry about down the road is worth the price of admission.

Good luck, hope you get it sorted.