2021 Chevy Traverse AWD problem

[JTK]

My 2021 Traverse LS AWD is just shy of 70K miles. About a week ago I noticed when having it in AWD mode, you get a random, sporadic jolt or bump from the back end as you are cruising down the road, like the clutch in the rear carrier is toggling itself full beans on/off, on/off sporadically. This is happening when there is no need for AWD to be engaging in the first place. No other noises, no binding when turning and no codes or warning lights. AWD engages and disengages normally with the dial control. The issue completely goes away in normal 2wd/FWD mode.

Since it was due for it's yearly state inspection, I had it at a shop I know and trust today to troubleshoot this. The shop was able to feel the concern, but they have no idea what is causing it. They scanned for codes for which there were none. They checked the clutch fluid level and condition, t-case and rear diff oil were also good. He did say the clear-greenish clutch fluid was a little below the fill/overflow plug, but he didn't believe this could be the problem. He even ran it up on a lift to listen/feel for AWD drive line issues and it all looks and sounds good. He couldn't find any similar concerns for a 2018+ on identifix or whatever they use online either. Totally stumped.

The rear tires are slightly cupped and worn a bit more than the fronts due to me slacking on rotations. Not enough to fail inspection. That could possibly be it, but I'm grasping at straws here.

About 2yrs and 40K miles ago, I drained and refilled the t-case and rear diff with synthetic 75w90. I have a thread floating around on this site in regards to that. I have also done multiple transmission drain/fills.

 

[redhat]

Out of curiosity, have a scan tool? Are any front ABS wheel speed sensors dropping out or sporadic thus making the PCM think a wheel is slipping?

 

[97prizm]

Typically awd isn't selected like old school 4wd. The vehicle puts power to the wheels needed. Is this somehow different?

 

[GSCJR]

ABS wheel speed sensors dropping out or sporadic thus making the PCM think a wheel is slipping?

This could be the cause, I was experiencing the same thing as you, @JTK. Fast forward a few months and I got a Christmas tree dash. The solution, a RR speed sensor and the intermittent bump from the rear end is gone.

 

[JTK]

Out of curiosity, have a scan tool? Are any front ABS wheel speed sensors dropping out or sporadic thus making the PCM think a wheel is slipping?

I didn't try with my cheapy $29 reader. As soon as I discovered this issue last week, I called the shop. The darling bride uses AWD mode when the roads are slippery and apparently she didn't notice the jolting. It could jolt 6x in 10sec, or 1-2x in 10sec, but it's constant. I used the terms random and sporadic. It's constant, but not at regular intervals. You'd think if is a WSS or tone ring, I'd get ABS activation or trouble lights.

Typically awd isn't selected like old school 4wd. The vehicle puts power to the wheels needed. Is this somehow different?

Yes, it FWD all of the time. If AWD mode is selected, power is only sent to the rear wheels via a wet clutch built into the rear carrier, if front wheel slippage is detected, up to ~15mph. At ~15mph+ no AWD. If FWD mode is selected, AWD never activates.

This could be the cause, I was experiencing the same thing as you, @JTK. Fast forward a few months and I got a Christmas tree dash. The solution, a RR speed sensor and the intermittent bump from the rear end is gone.

I'm with you on this, but why only in AWD mode and no ABS activation/issues have presented yet.

I truly appreciate any feedback or ideas on this.

 

[GSCJR]

I'm guessing because it's a rear sensor that's dropping out (like mine was, RR). I'm also wondering if it's happening so fast and infrequently, that the control unit won't store a code. @JTK, try getting a scanner connected and look at wave forms and/or wheel speed readings.

 

[redhat]

It could be so intermittent that it doesn’t set one. Maybe proof of this is other GM logic like on 800 trucks where you get random ABS activations when coming to a stop many times before a hard fault light sets.

 

[JTK]

I'm guessing because it's a rear sensor that's dropping out (like mine was, RR). I'm also wondering if it's happening so fast and infrequently, that the control unit won't store a code. @JTK, try getting a scanner connected and look at wave forms and/or wheel speed readings.

I think my next move will be to borrow a co-workers scan tool and try to pull live data from all 4 WSS's What's odd to me about this whole thing is, this AWD system on these GMs (Traverse, Equinox, etc) is only intended to get you moving. It's supposed to completely drop out at speeds over ~20mph. It's not a fancy torque vectoring AWD system. It simply kicks the rear end in to the degree necessary to get the thing moving (get all 4 wheels rolling at the same speed). I'm getting the thumps/bumps from the rear at speeds up to 55mph and possibly beyond. Just haven't tested it going faster.

 

[repairman54]

self delete

 

[GMBoy]

1ST THING IS TO UNDERSTAND HOW YOUR 21 TRAVERSE AWD WORKS:



The disconnect-design power transfer unit has the ability to internally engage and send power and torque to the rear propeller shaft, activating AWD mode. Shifting is performed by a PTU mounted actuator motor, internal linear and rotary cams, and shift collar. The actuator motor operates as-directed by the rear differential clutch control module to perform the shifting operations.


During normal driving situations, the power transfer unit operates in FWD mode with no rotation of the rear propeller shaft. The rear differential clutch control module monitors wheel slip based on the inputs from the wheel speed sensors and/or vehicle speed sensor. When the vehicle experiences a wheel slip condition, the control module sends a pulse width modulated (PWM) signal to the PTU actuator motor. The actuator motor rotates the worm gear and rotary cam, moving the shift collar to engage AWD and propeller shaft rotation. AWD mode will remain active until the slip condition has stopped. The process would repeat if wheel slip is detected again.


FROM HERE WE CAN SEE YOU HAVE DIFFERENT DRIVE MODES TO CHOSE FROM:

• Tour Mode —Operates in FWD to improve fuel economy. Use this mode during normal driving operations.
• Sport Mode —Improves vehicle handling and acceleration on dry pavement. When active, Sport Mode modifies steering efforts, transmission shifting, AWD torque, and suspension tuning, if equipped.
• AWD Mode — Provides drive torque to all four wheels. Select AWD to improve traction and control on slippery road surfaces, such as gravel, sand, wet pavement, snow, and ice. When in AWD Mode, the AWD Mode indicator light will be on.
• Tow/Haul Mode —This feature can assist when towing or hauling a heavy load. Use this mode to assist in maintaining desired vehicle speeds when driving on downhill grades by using the engine and transmission. For AWD vehicles, choosing Tow/Haul Mode also engages AWD mode.

WITH ALL THIS SAID - I WOULD 1ST DRIVE IT IN TOUR MODE (FWD ONLY) AND SEE IF THE ISSUE STOPS. WE ARE TRYING ISOLATE SYSTEMS HERE. IF IT GOES AWAY THEN WE DO NEED TO LOOK AT THE AWD SYSTEM BUY RULING OUT ANY CODES, AND WHEEL SPEED SENSORS ETC THAT EFFECT ACTIVATION OF THE AWD SYSTEM TO THE REAR AXLE. MY GUESS IS THERE IS SOME PLAY IN THE PTU ACTUATOR.

(sorry about all CAPS - that was to distinguish between me and the copied service information)

 

[repairman54]

When you serviced the rear diff did you use a LS oil ? Poster on the Traverse forum didn't and had ''jolts''. Using a LS oil cured it. The Traverse is not a G80 type diff. and specs a LS gear oil and if a dual clutch it also has a Pentosin hydraulic fluid section.
I've got a dual clutch in my '20.

 

[JTK]

1ST THING IS TO UNDERSTAND HOW YOUR 21 TRAVERSE AWD WORKS:....

Thank you! I appreciate the info. I do understand how the system works. I did some poking around and sorted it out a few years back as I also own a 2021 Equinox AWD that has basically the same system. There is very little info out there on this ~6yr old system (began production in 2018), which is good and bad. My Traverse LS model does not have touring or sport modes. Just 2wd, AWD, off-road and I believe tow/haul mode. It does the thump/bump from the rear in AWD and off-road mode.

When you serviced the rear diff did you use a LS oil ? Poster on the Traverse forum didn't and had ''jolts''. Using a LS oil cured it. The Traverse is not a G80 type diff. and specs a LS gear oil and if a dual clutch it also has a Pentosin hydraulic fluid section.
I've got a dual clutch in my '20.

The gear oil I used at ~35K miles was Valvoline full synthetic 75w90 that has limited slip additive in it. I've only done that one drain/fill cycle on the rear diff and transfer case / power transfer unit so far. ~70K on the vehicle currently. I will do another if I can get a break in the weather. I don't think it's stopped snowing since I started this thread and it's -2degF today.