4wd issue

05 Envoy Denali (5.3 V8) having 4wd issues
I don't have 4wd engaging.
I've read this VERY helpful thread...and I still have some questions.

I can hear the encoder motor on the t case...but it makes the same whirring sound twice. then clicks and stops.
I can't hear anything from the front...so I'm guessing the axle disconnect needs some work.

But here's the rub...the light never moves off of 4hi. and It's clearly still in 2wd. so I'm guessing the encoder isn't sensing any movement...or the whole t case motor is bad?

In any case...with the driver front wheel in the air, I turn the wheel and the front driveshaft spins. All 3 other wheels are on the ground.

So...since the front driveshaft spins that would need to mean either
A. the T case isn't really in 4wd.
B. the T case IS in 4wd and the clutches are worn out and slipping...hence why the driveshaft can spin.

Would the axle disconnect cause the issues with the front driveshaft?
Also...while I'm asking...what's the harm in installing the AWD front axle disconnect. Leave the axles together all the time and let the t case be the only thing determining if I'm in 4wd or 2wd.
WIll it throw codes or anything with that module not plugged in?


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It would help if all of your Vehicle Profile Information was keyed in. The attached video may point you to the "Ground Bonding Wire Culprits" that often are the Last Places that gets Checked but well worth checking here FIRST before condemning any of the Transfer Case Sub-Systems or Modules.

As for the AWD Transfer Case Swap.... that is an interesting idea. If you Google around... Rumor has it that an even sturdier AWD coming out of a Cadillac Escalade might be a possible candidate for being Smoother and More Robustly "Engineered" than the GM OEM TC installed down there right now. You might investigate the possibility of moving one into the Envoy-Denali Platform; assuming that the Caddy AWD Unit will fit without having to resort to any Exotic Modifications:

"Smoother and Stronger Always Sounds Nice ... But It Also Depends Upon The Price..."

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If you install an AWD disconnect, you will have to leave the actuator connected so as to not get a "Service 4x4" light and error. Put it in a sandwich bag and zip tie it out of the way.

You might get a slightly lower MPG and will get a bit more wear on some parts as you will be spinning all the parts 100% of the time (like the diff and driveshaft). With a real disco, you're only spinning the spider gears inside the diff from the left axle.


I think there's something with your encoder motor. You shouldn't be able to turn that wheel or the driveshaft if the TC is supposedly in 4hi. It's especially wonky if you put the switch on 2hi and it still shows as 4hi. Now if you're putting it in A4WD, that is normal as the TC is only engaged when there is rear wheel slippage.
I think so too.
I'll tear apart the encoder motor and check it out. Repair/replace as needed.
I'll report back if that's the fix.
Have some camaro work to do here before the envoy gets attention
So...new encoder, new front disconnect motor (tore the disconnect apart, regreased it, looked great), and new switch.
Still no 4wd.

The switch will light up the 2wd and 4hi lights at the same time. Sometimes 4hi will blink/flash but then go back to solid.

Used a snap-on scanner and found codes C0321 and C0379
Suspecting a TCCM...this is an 07 so I know the tccm is not as likely as earlier years...but at this point, I'm not sure where else to go/check

Any input is greatly apprectiated


If it was the TCCM, you'd get a code for it and not one for specific components. You could grab one from a junker at a pick-n-pull cheap as a test. Grab a switch while you're at it.

I'd check the wiring and connectors since you have a new encoder and disco actuator. Grab the manual from the link in my signature, look up the schematics and trace the wiring to the TÇCM.


Well-Known Member
So...new encoder,
For clarification...new encoder? (The round variable resistance ring inside, with 3 wire harness) or new Encoder Motor assembly (the whole deal, motor, encoder ring, brake etc)??

A couple months back I replaced the encoder rings in both my 05 Yukon and my 02 Trailblazer. My motors were fine so I only replaced the cheaper encoder ring inside the units. Having torn the old one(s) open it becomes readily apparent why the encoder rings fail with age. The little sweeper pickup thingys sit in the 2wd drive position for most of their lives and chew their way into the resistive material leaving depressions that result in unsteady voltage values going back to the TCCM.


I also had at least one cracked solder joint.
I cracked the ceramic getting the thing apart.



You can get those rings separately? Never heard of anyone doing this before. Maybe it's gone bad again.


Well-Known Member
Maybe it's gone bad again

No, no! Both of mine are fine. I was just looking to be sure @MaroonMonsterLS1 had replaced the whole she-bang or not.

And yes these are available if you're willing and able to swap them out and save a few bucks. Maybe I should do a writeup, I have a boatload of pictures of the operation.

Yes, just the encoder ring. Not the whole motor. I actually had a 2nd encoder motor laying around, so after it still didn't work, I put the NEW ring on that motor, and get the same issue.

New front axle disconnect motor...and I'm getting a code for it too.

It has a brand new switch.

-front motor
-encoder ring
all brand new

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