I have an 07 H2 with just over 30k miles. recently, the transmission started to act up. It would have a hard time shifting from 1-2. After it would finally make the shift there would not be an issue for the rest of the commute. This issue was much more common if the truck wasn't allowed to warm up but it has happened warm too. I checked the fluid and saw that it was low. It must be a very slow leak since nothing is visible on my driveway. I filled it up and the problem went away but it came back despite the fluid level being ok. I also added some trans stop leak/seal reconditioner and that did seem to fix the leak.

At the same time this trans issue came about, I started having my speedo act up. Basically it will start to bounce around when driving. Usually its around a 10-15mph fluctuation but it has been more. This speedo issue will happen whether or not the trans had an issue that day with the 1-2 shift. I went to the GMC dealer. They suspected a possible speed sensor issue but ultimately decided that wasnt it. They said they called their tech assistance hotline but they were of no help since no lights are coming on and nothing comes up wrong on any scans of the vehicle and the vehicle is now running fine for them (they did experience both issues when they first got it in).

I picked up the vehicle last night and while the trans was fine, the speedo started bouncing around again this morning when cruising around 70mph. I've done some research online and on here but the only thing I found was the stepper motor issue but this does not really sound like that.

As far as the dealer is concerned, although they are at a loss, they feel that it is not the trans itself but possibly something electrical.

I really can't afford to pay them to start tearing down the entire truck hoping to find a needle in a haystack, so hopefully you guys can shed some light on this. Even if you haven't heard of this issue before, perhaps you know what some possible issues are or where I should be focusing on ie. things that can have an affect on the speedo and or trans.

TIA.

PS. I LOVE this truck. If I have to I'll take out a 2nd mortgage and have this entire truck rebuilt (I'm thinking diesel ). Lets hope it doesnt come down to this cause I can't afford that lol

 

I'm starting to wonder if the speedo issue and the trans happening around the same time were just a coincidence.

Was the steeper motor an issue for the 07 H2's?

 

Probably a speed sensor error and the truck is confused and doesn't know when to shift. I bet it's not a big deal. I would take it to a transmission shop and have it scanned.

 

If you live in So. Cal I can recommend a really good trans shop.

 

Unfortunately, it has gotten much worse. I drove the truck a couple miles to the store issue free. The drive home didn't go quite so well. The speedo started going nuts (no biggie) and than the trans started to slip. I had to nurse it home. It kept slipping and I'd have to pull over and stop. Once I did this, it would start working again for a short amount of time and than trans slipping. It would sometimes keep changing gears and other times it would just slip like I had it in neutral. Not a single light on the dash either.

This time, I took a video of it happening and hopefully that can help the dealer try to figure out wth is going on.

 

I wouldn't drive it anymore until you get it checked out. Let us know what the dealer says.

 

Absolutely. I parked it over the weekend and dropped it off at the dealer this morning (of course it drove fine for the most part).

I will def keep posted. You never know if this might help someone out in the future.

 

Just an FYI. a fairly common issue with chevys is the speedo cluster itself. there is a place the rebuilds them, I did forget the name as I'm no longer in the business but you should be able to find them on google. the issue that you are having is one of the symptoms.

 

I had a 05 1500 Pickup and the speedo when bad in it to except on the chevys there was a class action lawsuit by gm owners that forced gm to replace all of the affected vehicles free of charge fortunately mine was included in the lawsuit I am not sure why the hummers weren't covered as well I am sure that it is the same gauge cluster

 

UPDATE: (Sorry it took so long but I figure I should update this so anyone searching in the future has a possible fix to a similar problem).

Long story short, turns out the wiring harness was rubbing on the transfer case and it started shorting out. Its been a couple months since they fixed it and no problems since.