Good afternoon folks,

Now before folks start saying "There are other threads on this!" I've looked, and there seems to be some there, but not for the issue that I was told I'm having, similar, but not exact. So with that said, hoping to find some help.

I bought my 2007 Hummer H3 in 2014 or so, had a warranty with it after the fact (That I used extensively to basically replace everything from the ground up), and since the third year after owning the vehicle, I've noticed that the "Serv 4wd" light on the DIC pops up whenever I would go through a car wash or something, I tried to figure out what it was and so did several shops, to no avail, as most of the time by the time I got there, the light would be out and no stored codes, and yes the dealership was one of the shops I took it to and they just shrugged and said "Well, works fine now!"

So fast forward a bit and the light still comes on from time to time, FINALLY figure out that I've got some drain tube issues with the sunroof (I mean, unless you live in a desert, who hasn't?) So I got those (all four of them) fixed. The "Serv 4wd" light continued to come on after that on exceedingly humid days and I couldn't figure out why at all, so I was at a loss.

Figuring that I was sitting at around 230,000km by this point (I bought it at 151,000km), in 2020, it was time to get the transmission serviced. I took it to Mr. Transmission in St. Catharines, Ontario Canada, and I asked them if they could do an investigation for me into the serv-4wd, as I'd done everything that I could find tips on how to do (including replace the encoder shift motor, check the connectors underneath...at least the ones I could get to anyways. Put desicant packages inside the truck to kill humidity, etc...) But nothing seemed to work, so they said "Sure." So I got my transmission serviced, and the transfer case. They said nothing is wrong with the transfer case, but there is a "Short to Power" in the TCCM and it would need to be replaced.

So I was like "Great!" Call up the GM Dealership afterward that is local and asked them to see if I could get one. They sounded shocked and said that they couldn't find any, anywhere; so I looked around at a few wrecker yards that sell good parts that they bench test, and found two. First one I ordered never showed up, the company apologized and gave my money back, the second one I went and picked up, and had it for about 3 months after the fact.

So I went to install the 'new/used' part today, and after making sure the truck was powered down, unplugging everything properly, etc...I replaced the TCCM (little black box behind the glove box on the right side of the vehicle for North American users), and plugged the new/used one in. Waited, turned on the truck aaaaand...."Serv 4wd" popped up again.

SO! Does -anyone- have any insight on this? I'm kind of tired of taking it to the dealership to have them tell me 'just drive it', and I'm seeing if I can source a -new- TCCM at this point but I don't like my chances for a 15 year old vehicle at this point. Is there some kind of code machine that I have to have to make sure it is connected right? Or from what I've read, it should just be 'plug and play', no?

Any insight or help into this would be greatly appreciated, and side note: Has anyone covered the backing plates of these units in Marine silicone to waterproof them for a 'just in case' kind of thing? Only curious.

Thanks again in advance, and hope to hear from you guys soon. I love my truck but the 'ding-ding-ding' of the 'idiot light' on the dash is really starting to make me question my love...lol

 

Most certainly there's a code! Get a quality scanner and post the codes!
My magic crystal ball points to:

 

Thanks for that, I do have a Blue Driver OBD2 scanner tool, and I'll scan it again and post what results are here.

Hopefully I can get some insight, side note: The Random multi-cylinder misfire was a stored code, that was just bad spark plugs, fixed since then.
Though most of the codes that are there are historical codes so...I don't know. From what the Transmission shop told me, my transfer case, transfer case encoder motor, and whatnot works fine, though one of those codes tells me "Replace Transfer Case/Replace Encoder motor" which...if its fine, then wth? lol.

Anyways, the report is attached from the 'scan all system modules'.

 

B1390 & C0306 is CURRENT, check here:

 

Interesting, is this the same location for the H3? I'll have to see if I can snag a friend's lift and get up under there as my driveway is buried in snow/salt at the moment! Or would it be on the passenger side for the H3, as most of the electronic components (BCM, TCCM, Shift Control Motor, etc...) are mounted to the right of the vehicle?

Thank you for your help, by the way. I really do appreciate it, I don't need anymore white hair, I'm only 35! XD

 

Whipper-snapper, I'm soon to be 56, yet I can still crawl under my ride when I need to, not now since it's in 2ft of snow. Battery is on the drivers side, CHECK GROUNDS there.

 

Oh, when I need to crawl under my truck, believe me, I do/will, and have quite often! But yeah, snow/ice + crawling on back = bad at the moment. Lol. Thank you! I'll check it out tomorrow hopefully once I can get a friend with a lift's help, either that or a garage XD

Thanks again! I'll post an update if this works!

 

When you find them, remove bolt, and clean all mating surfaces(bolt, frame,terminal) until you get that silver finish appearance. Then properly secure,tighten&protect.
Btw, the question noted by Doc Olds Do you still have those crappy azzed oem battery terminals?

 

I don't have the crappy old terminals, had my battery die twice on me due to a parasitic draw a few years back (thankfully, that's been resolved, was a faulty headlight switch/dome light/fog light module) and the CAA guy saw the old terminals and replaced them with much better ones.

Haven't had a chance to crawl under there yet, but I will, question though, will I need to pull the inner fender well out to get access to this? Or will it be as simple as just getting under there and it'll be rather obvious?

 

IDK never had to look for a ground? 102 & 103 is on the block, 105 & 106 lf & rf inner wheel wells.
More info on ground locations here::::>>> Hummer H3 Wiring