I have a 2003 GMC Envoy 4X4 that is having issues with the 4WD engaging (it does'nt). I have installed a new TCCM unit and a new transfer case encoder motor. I still do not have 4WD engagement. When I had it on jackstands (driver side both wheels off ground) changing out the the TC motor I noted that the rear wheel rotated in gear in 2WD and both front and rear wheel rotated in 4WD. But when all four wheels on ground the front axle is not getting drive power in 4WD. What I have not done and am thinking about is having the electronics flashed although the TCCM was a used unit. Also the transfer case lube is coming up on 50000 miles. Any thoughts?
4WD doesn't work
- Thread starter fechnerj
- Start date
If you have your own GM Tech2 or access to one... your suspicions are right on the money regarding the need to re-flash as per this link...when you see the script stop yellow line at the top just press "Stop It" and the rest of the page will completely open up... it is NOT necessary to interact with the on-line mechanic to obtain alll the information you require there:
https://www.justanswer.com/gm/5ys1b-transfer-case-my-04-will-flashed-reprogrammed.html
https://www.justanswer.com/gm/5ys1b-transfer-case-my-04-will-flashed-reprogrammed.html
Mooseman
Moderator
Normally a used TCCM does not need to be reflashed. I seems to be working correctly and you're not getting the service 4x4 light (I assume). If your fronts aren't getting power but the drive shaft is spinning, I would be that either your disconnect is bad or the intermediate shaft stripped.
I am not getting a 4X4 service light. Is there a clutch like device in the transfer case? I ask because as stated I got both front and rear wheel rotation with driver side on jack stands both wheels off ground. When wheels are down though no traction on front axle.
Mooseman
Moderator
So you get driver front wheel turning with just two wheels off the ground (which is dangerous if you have a G80 locker in the back) but with all four off the ground, fronts don't turn? With two off the ground, can you stop that wheel by hand? What about when you jack passenger sides? (do this only if you have a rear open diff).
I still think it's your disconnect or intermediate shaft.
I still think it's your disconnect or intermediate shaft.
To clarify I don't have locking rear diff. What specifically is disconnect and intermediate shaft and where are they located? With all four wheels on the ground I don't have front drive. With driver side two wheels off ground I have drive at both wheels. I did not try to stop the front wheel turning.
Mooseman
Moderator
The disconnect is on the passenger side of the oil pan and disconnects the right shaft. The intermediate shaft is what connect the disconnect from the diff to the disconnect.
This article on ORTB shows how to rebuild the disconnect but also shows where it is located.
Front Axle 4WD Disconnect Rebuild
This one shows transfer case operation:
Transfer Case Operation: NVG 226 (NP8)
And this one is especially good:
Diagnosing the 4WD System
We also have one but it's not as detailed:
4WD not working? Step inside.
This article on ORTB shows how to rebuild the disconnect but also shows where it is located.
Front Axle 4WD Disconnect Rebuild
This one shows transfer case operation:
Transfer Case Operation: NVG 226 (NP8)
And this one is especially good:
Diagnosing the 4WD System
We also have one but it's not as detailed:
4WD not working? Step inside.
So I ran thru the diagnostic chart and it appears the TC is the problem. With pass front tire off ground I get tire rotation and prop shaft rotation. With both front off ground I get CW and CCW tire rotation and prop shaft rotation. With pass front tire off ground and driver front blocked from rotating I turned the prop shaft with a strap wrench. Wife could not stop pass front from rotating which tells me all is well from the output of the TC thru the front diff to both front tires. Looks like I'm shopping for a used/rebuilt TC but before I make that leap---- way back when I first started this I suspected the TCCM unit was bad so I replaced it with a NOS unit. After this all the lights on the switch responded correctly and the motors make the expected noises when engaging AWD 4Hi 4Lo. It is a bit more challenging to get into neutral but it does go just not as readily as it did with the original TCCM. Reading the operational info you got me thinking that there is a clutch involved with 4WD and maybe the new TCCM isn't doing the job of communication with the clutch pack. What do you think?
Mooseman
Moderator
All the TCCM controls is the TC and disconnect. The internal clutches are engaged by the shaft rotated by the encoder motor. Have you had a look at the fluid yet? It is often forgotten, overlooked or neglected as it has a relatively short 50k mile change interval. It has been known to destroy TC's.
I would also put back the original TCCM.
I would also put back the original TCCM.
Just to update the situation. I got a rebuilt TC and reinstalled the original TCCM. This resulted in only 2WD and 4Lo. Did not have any response from Auto 4Hi or Neutral.
Took the vehicle to GM service shop where they pulled several codes cleared the codes and reloaded the software. Vehicle now works in all 4X4 modes. The dealer didn't treat me too badly only charging $206 for a couple hours work which included the above and pulling the encoder motor to check the internal contacts. All ok there.
By the way pulling the original and reinstalling the rebuilt/used TC was a PIA. That job took me about 3 hrs to get the old one out and 12-16 hrs to get the replacement one installed. If you are going to do work that requires carefully positioning and lifting a TC or transmission invest in a transmission jack.
By the way when draining the oil from the original TC there were fine metal particles and one piece of metal about 1/2 inch long X 1/8 X 1/8 square in the drain pan. Definitely a problem going on there but I did not open it up because it was a return core.
Thanks for all the help and suggestions especially to Mooseman.
Took the vehicle to GM service shop where they pulled several codes cleared the codes and reloaded the software. Vehicle now works in all 4X4 modes. The dealer didn't treat me too badly only charging $206 for a couple hours work which included the above and pulling the encoder motor to check the internal contacts. All ok there.
By the way pulling the original and reinstalling the rebuilt/used TC was a PIA. That job took me about 3 hrs to get the old one out and 12-16 hrs to get the replacement one installed. If you are going to do work that requires carefully positioning and lifting a TC or transmission invest in a transmission jack.
By the way when draining the oil from the original TC there were fine metal particles and one piece of metal about 1/2 inch long X 1/8 X 1/8 square in the drain pan. Definitely a problem going on there but I did not open it up because it was a return core.
Thanks for all the help and suggestions especially to Mooseman.
Last edited:
Just to update this thread.
I towed this truck (2003 Envoy SLT) behind a motorhome for several years. To do this it is necessary to shift the transfer case into/out of neutral. I followed the instructions given in the owners manual which is listed on page 2-28 in my manual. Stay with me here because I believe that this proceedure is the root cause of my transfer case failure.
Shifting into NEUTRAL
1 Set the parking brake.
2 Start the vehicle.
3 Put the transmission in NEUTRAL.
4 Shift the transfer case into 2HI.
5 Turn the transfer case know all the way past 4LO and hold it there for a minimum of 10 seconds. The neutral indicator light will come on.
6 Shift the transmission to REVERSE for one second, then shift the transmission to DRIVE for one second.
7 Place the transmission shift lever in PARK.
8 Turn the ignition to LOCK.
Shifting Out of NEUTRAL:
1 Set the parking brake and apply the regular brake pedal.
2 Start the vehicle with the transmission in PARK.
3 Turn the transfer case knob to the desired shift position (2HI, 4HI, or A4WD).
4 Put the transmission in NEUTRAL.
5 After the transfer case has shifted out of NEUTRAL the indicator light will go out. Shift the transmission lever to the desired position.
Quote "A re-engagement sound is normal when shifting out of NEUTRAL"
Again, the above is for my 2003 Envoy.
In 2018 I started shopping for a newer Envoy cause we think it's a great vehicle for the rural area we live. I found a 2009 Envoy SLT, low mileage, great shape and bought it.
Thumbing thru the owner's manual I noticed that the instructions for shifting into/out of NEUTRAL were very different. Wow, what a difference. NO GEAR RE-ENGAGEMENT SOUND!!!
The differences for the 2009 are these:
Shifting into NEUTRAL
Between step 6 and 7 above, TURN THE ENGINE OFF, AND PUT KEY IN ACCESSORY POSITION.
Shifting out of NEUTRAL
Delete step 2 in the 2003 instructions and insert the following:
2 Turn the ignition to ON/RUN with the engine OFF.
2a Put the transmission in NEUTRAL.
Bottom line no gear noise and it's clear to me that sometime between 2003 and 2009 engineers realized that gear noise is bad, no gear noise is good.
I strongly believe that the noise of gears clashing, even mildly is not a good thing and eventually knocked a tooth off in my case, which was discovered when draining the case. I don't know the full extent of damage that may have occured in the case because I didn't open it for inspection because it was a core exchange situation. All I know is new transfer case fixed it.
I towed this truck (2003 Envoy SLT) behind a motorhome for several years. To do this it is necessary to shift the transfer case into/out of neutral. I followed the instructions given in the owners manual which is listed on page 2-28 in my manual. Stay with me here because I believe that this proceedure is the root cause of my transfer case failure.
Shifting into NEUTRAL
1 Set the parking brake.
2 Start the vehicle.
3 Put the transmission in NEUTRAL.
4 Shift the transfer case into 2HI.
5 Turn the transfer case know all the way past 4LO and hold it there for a minimum of 10 seconds. The neutral indicator light will come on.
6 Shift the transmission to REVERSE for one second, then shift the transmission to DRIVE for one second.
7 Place the transmission shift lever in PARK.
8 Turn the ignition to LOCK.
Shifting Out of NEUTRAL:
1 Set the parking brake and apply the regular brake pedal.
2 Start the vehicle with the transmission in PARK.
3 Turn the transfer case knob to the desired shift position (2HI, 4HI, or A4WD).
4 Put the transmission in NEUTRAL.
5 After the transfer case has shifted out of NEUTRAL the indicator light will go out. Shift the transmission lever to the desired position.
Quote "A re-engagement sound is normal when shifting out of NEUTRAL"
Again, the above is for my 2003 Envoy.
In 2018 I started shopping for a newer Envoy cause we think it's a great vehicle for the rural area we live. I found a 2009 Envoy SLT, low mileage, great shape and bought it.
Thumbing thru the owner's manual I noticed that the instructions for shifting into/out of NEUTRAL were very different. Wow, what a difference. NO GEAR RE-ENGAGEMENT SOUND!!!
The differences for the 2009 are these:
Shifting into NEUTRAL
Between step 6 and 7 above, TURN THE ENGINE OFF, AND PUT KEY IN ACCESSORY POSITION.
Shifting out of NEUTRAL
Delete step 2 in the 2003 instructions and insert the following:
2 Turn the ignition to ON/RUN with the engine OFF.
2a Put the transmission in NEUTRAL.
Bottom line no gear noise and it's clear to me that sometime between 2003 and 2009 engineers realized that gear noise is bad, no gear noise is good.
I strongly believe that the noise of gears clashing, even mildly is not a good thing and eventually knocked a tooth off in my case, which was discovered when draining the case. I don't know the full extent of damage that may have occured in the case because I didn't open it for inspection because it was a core exchange situation. All I know is new transfer case fixed it.
Mooseman
Moderator
Talk about a long term update! Thanks for the info.
Did you try the newer procedure on the 2003? I'd have to check if my 2007 has this newer procedure.
Did you try the newer procedure on the 2003? I'd have to check if my 2007 has this newer procedure.
Mooseman
Moderator
Yes, I did use the newer procedure on the 03. Same good result, NO GEAR NOISE!!
I believe the key to getting into and/or out of neutral is knowing specifically what is happening inside the transfer case. This is very likely far beyond the capabilities of the common owner.
Speculation on my part: Maybe they found owners were confused by the prior directions and were shifting out of neutral with the engine running and the transmission in neutral rather than the required/stated drive position? This will cause the input shaft gear to be spinning when the hi/lo range collar is moved to engage it. That will surely result in both gear crash noise and potential damage.
Speculation on my part: Maybe they found owners were confused by the prior directions and were shifting out of neutral with the engine running and the transmission in neutral rather than the required/stated drive position? This will cause the input shaft gear to be spinning when the hi/lo range collar is moved to engage it. That will surely result in both gear crash noise and potential damage.
The gear clash was when going into PARK at the end of the INTO NEUTRAL move (sounded like chattering) and then again when shifting out of PARK at the beginning of the OUT OF NEUTRAL move (more of a distinct clunk).
Ahhh !! That is the same as shifting into Park while the vehicle is still moving! Once the transfer case is in neutral the output shaft of the transmission is free to rotate. And with the engine running there's nothing to stop it. In effect it's the same condition as if the vehicle still moving as far as the transmission is concerned.
Engine started, Transmission in Park, Transfer Case in Neutral.
Trans ouput shaft held by Park Pawl (or whatever they call it).
Transfer case output shaft free, not engaged with anything.
Attempt transfer case shift out of neutral.
At this moment the TCCM tries to rotate the encoder/shift motor a small amount to move the hi/lo range shift collar with either the input gear or the planetary shell depending on what position was selected at the 4wd shift switch. If the gearing is not aligned correctly the gear teeth butt up to each other but cannot mesh until one or both of them move a little. I believe there is a spring loaded component in there so nothing is broken while the encoder/shift motor is trying to force the hi/lo shift collar to engage.
If the hi/lo shift collar cannot move and get something engaged before the transmission is shifted out of Park, then the transmission output shaft is going to spin a bit when Park is released and then that shift collar will move to engage in either hi or lo range as directed by the 4wd switch/TCCM.
This clunk will be the same clunk heard when shifting into or out of lo range since it is actually the same items being moved/engaged/disengaged.
I would always treat the shift out of neutral the same as shifting into or out of lo range. That is, I allow the vehicle to move ever so slightly during the shift to aid in getting the gears aligned. I have sometimes actually rocked the vehicle using my left leg on the ground through an open drivers door!!
Mooseman
Moderator
Yep, that would be the parking pawl ratcheting inside the transmission trying to stop the output shaft. With the transfer case in neutral and the transmission in neutral, there is nothing to prevent the transmission's output shaft from spinning from residual friction inside the transmission. If the engine is running while shifting into neutral, I would shut the engine off and wait a few seconds before trying to shift it into Park to allow the output shaft time to stop on its own.
As an aside, I have to admit that I've never seen a GMT360 being towed behind a motorhome. I've seen lots of Jeeps, small manual cars and a Tahoe (must be rich!). The Envoy/TB would be a nice mid-sized SUV to tow.
I'm following all the technical reasons that you presented for the sounds that I heard and agree with your analysis. Thanks for the full explanation. Sometimes, I towed a Chevy Tracker 4X4, the small version TOAD, Used the Envoy most of the time because DW prefered the comfort and I could carry more stuff for day trip fishing, site seeing trips, etc. Diesel motorhome didn't care what was behind. I don't have the MH anymore, sold about 3 years ago, and don't have need to use the neutral function. I guess that explains the delayed time to post the update that you mentioned.
I still own the two Envoys, sold the Tracker.