armgmc

Found something similar to my reversing problem they reference it as "torque reversal" http://www.gm-trucks.com/forums/topic/130945-transmission-problem-speedo-reads-zero-07-nbs/

Got the code scanner coming over in a little bit. Took the shift motor off today and the gear on the motor itself that engages the gear inside the TC is locked up. Is that supposed to be like that? I would assume it would free spin but IDK. Found a junk yard TC for $375 but not sure if I want to go buy it without further diagnosis. I tried switching from 4lo to 4hi with gears disengaged to see if something was locked up in the TC but couldn't get the motor to attempt to move for me. I'm thinking those error codes have disabled signal voltage to the TC motor and won't allow it to do anything. Thinking I may need a TCCM reflash or maybe just a new TCCM

yeah it didn't grind on me today but it usually does that in 2wd and the stabilitrak and TC does work. not sure how that whole system works though. Would like to have it hooked up to a scanner but im 30 miles from a stealership and don't want to drive that far in 4low. I have a friend that is a mechanic and i'm sure he's got a pretty fancy ODBII scanner so I'll see if he won't bring it home after work tomorrow and scan it for me.

What I'm really hoping for is that the gears inside the shift motor are what's grinding or slipping when reversing. Seems to be a fairly simple piece to open up and inspect once off of the tcase. This thing has the stupid auto 4wd BS with stabilitrack and traction control so I'm thinking that when I spin in reverse it's trying to engage the auto 4wd .

I'm gonna look for fuses or relays tomorrow, any idea what they'll be labeled as? If it's somewhat easily accessed I'll probably pull the shift motor and see if it will attempt shifting when not bolted onto the tcase.

Any idea why the encoder motor isn't even trying to shift? Any fuses or relays to check? possible bad TCCM?

Will do, never been into a tcase before so I'm not sure how competent I am with rebuilding it. Got some good friends with experience though so maybe they can help me with the rebuild.

Battery off for close to an hour didn't help anything. No noises when switched to 4 hi. Doesn't seem like the motor even tries to switch it. Usually you can hear it click to try and change it from 4 lo to 4hi but nothing at all.

Thanks, I'm probably gonna tear into it tomorrow and see what I can find. I'm off of work for now so I can afford to not have it for a few days anyways. Not sure about the tcase and what kind it is. Never really paid attention to it at all. I'll either look for a scrap yard tcase or rebuild this one if it's feasable. Kinda strange that it would go bad with only 130k miles but I dont know the trucks history from before me too well. Checked for DTC's and my innova 3130 didn't show anything wrong. It may not read tcase problems not sure. Got the battery unhooked now, about to go fire it back up and see if I can get back to 2wd.

I have a scanner here, not sure if it'll read the TCCM or not but I'll try in a few minutes. Getting it out of 4 low would be nice but I stil lneed to find the problem for future use.

To elaborate more on the reverse grinding it's not constant. When it happens it's loud as hell and kind of winds down like it's slipped a gear and will eventually catch I believe but I usually slip back up into neutral to stop it. Don't do it all the time only on heavy acceleration in reverse. First time it done it I was backing a trailer in my yard and slipped a little on wet grass.

Hey guys, first post here. I have a 2007 GMC SLE (new body style) crew cab z71. I've owned the truck a little over a year and theres been a few occasions since i've owned it where while reversing in 2wd or 4wd that something would slip and cause an extremely loud grinding noise almost everytime the wheels spin a little bit (hard acceleration). After realizing this happens I always try to easily accelerate when reversing but sometimes it will do it anyways. I've never had anyone close by to tell exactly where it's coming from but I suspect the transfer case. Tonight I went down to my hunting spot to just check it out and before leaving I thought I'd put it in 4low (turn knob) and maybe keep from spinning as I backed up the hill. after I got out of the spot I was in I tried going back into 2hi or 4 hi but the tcase never would shift back out and the service 4x4 light was flashing on the dash. Wasn't any loud clanks or grinding during all of this so I'm not really sure what went wrong or where to start looking. I'm gonna take it to my shop tomorrow and see what I can find but just wondering if anyone has ever dealt with the problem before. If it weren't for the grinding I'd suspect maybe an actuator but I feel like that's part of my problem. Thanks in advance for any help.