[Deadhead]

Hey,
I have a GMC that began to show a 4wd Msg. I checked fluid, fuses, cleaned the ground contact for the harness & replaced the switch as that was the most common issue. I reset the computer after I replaced the switch. It now shows no Msg, but no indicator lights on any of the switch functions from 2wd on down. switch inoperable. Wondering what to do next. I am leaning towards the TCCM since vehicle sat in sunlight directly on that corner of the dash for some time during some intense heat. Figuring it could have toasted the circuitry and if it is not "waking up" could be the cause for no Msg. Worked fine until Msg came up, so less inclined to encoder motor. Have had bad experience with dealer, and the local shops I have used are in some kind of drama - one the main guy just passed away, and the other the guy is threatening to move to FL, so all his guys have fled. Thanks for any help

Bruce

[ponchjoe]

If you replaced the switch it sounds like you got a bad one with no lights. Is this a autotrac or manual shifted transfer case? If auto have you checked operation at the actuator on the frt axle? There are electronics in the transfer case as well like encoder motor and position sensor that could be faulty. Info is all over the internet about this stuff. The question is where to start which you did, but maybe the switch is bad.

[stevep]

Bruce, if those vehicles had the 4x4 module in the RF kick panel, water would leak into the truck and on to the module. Try unplugging the module and see what happens. See if there is evidence of water intrusion too.

You can try tapping the encoder motor and if it starts working, replace the motor.
A scan tool will tell you if the switch is working.

[Deadhead]

Yes! There is a ton of info. I feel like I read all of it. I wondered if I got a bad switch too. It lights up as in backlight, but no deal on the indicators for the position, which was also the case with the one I replaced. Some of the posts I read said that if it was just this switch that it would not throw any usable code. Mine is not the autotrac, but it is electronically operated via the switch on the corner of the dash.

Steve-
I think that my TCCM is in the dash behind all the vents etc. I will remove kick panel to check and see, bc that is easy, but pretty sure for '01 it is back in the dash. There is conflicting info on this. Bunch of crap has to come out to get to it which is why I am trying to get some more info 1st. I think I tried banging on the encoder motor. I rotated the DS etc. too, but will try again.

Thanks for the ideas and replies!

[pontiacmark]

I ended up helping a friend replace the 4WD module on his similar year 1500. It would not switch out of 4WD.

[Deadhead]

Was able to use a scanner & got code U1026, which would seem to confirm TCCM. Ordered one and will install soon & report back.

[Deadhead]

OK, so before I installed the TCCM, I scanned again, and there was no U1026 code present current or in history. That seemed odd to me, but whatever.

I put the Cardone TCCM in and there was no change. All the lights were off on the selector switch, and still no communication in the system at all. Checked fuse on side of dash = fine. Pretty sure I did the correct routine of unplugging that fuse with battery disconnected, and plugging in while vehicle running to try to wake up the TCCM. No result there either.

I disconnected battery etc., and put the old switch back in, which had originally been giving the orange lights next to each selection, but not responding when the 4wd trouble light showed up. It too now has no indicator lights, and no change in codes or any of the rest when scanned. Wires and connections seem fine. No damage anywhere I can find.

Kind of stumped here. It is like the circuit is totally open somehow, and not communicating at all. Not sure what the next step is. I guess keep working my way through the parts. Sensor on the front axle next? Seems like if the motor on the TC was the issue, I would be getting something other than just a lack of communication.

Thanks for any help with this problem

[ponchjoe]

I think I remember there being some grounds to check on the frame under the drivers door if ours are the same. Is that the grounds you cleaned in your original post?

[johnta1]

Is this TCCM thing on the transfer case?

My 2003 is supposed to be the switch on the transfer case.
It is what tells the computer where it is at.
If it doesn't work the computer doesn't know what to do.

Mine generally is the 4 Wheel Switch on the dash you push, but if it's not that then it is the one on the transfer case.

I haven't put mine on because I hardly ever need 4 wheel drive.
Mine shows different gears when it starts (light by the gear switch).
Sometimes says it is in Neutral or even 4 Low. But the actual transfer case is still in 4 H. (or whatever it is actually in)

From the description on mine, the computer when starting goes through each gear position to see where the switch is at.
Sometimes it can't complete the sequence, so it stops at whatever last position checked was.
(it doesn't actually move the transfer case lever)

[Deadhead]

I have gone over the grounds. I looked at them again today, and they have crud around them since I cleaned last, & I can check again, but that has not fixed my issues in the past. I did put anti-corrosive goop on them when I cleaned and put back, so it should be OK. I may try running a wire direct to battery to see if that resolves it.

TCCM is in the dash. Computer box for lack of a better term.

[johnta1]

What is the transfer case designation?

Mine is NP-8 which has the problems.
Think they may be for 2003-2007 or so.
(probably doesn't apply)

On my wife's 2000 Jimmy the motor on the transfer case went out, which wouldn't let it shift gears.

Have you checked out the chevy truck forums?
There were a ton of stuff on the 4 wheel drive stuff on them.
Seemed to be a problem for awhile.

[Jerry H.]

I can't really help you out, BUT, in analyzing all the info you are getting you need to know what actual truck they are talking about. I was selling these trucks back then and IIRC, this was the changeover year and there was the old style 2001 and the new style 2001. I don't know which style you have, but the new style was a completely redesigned truck.

[Deadhead]

It is a 2001 2500HD. Pretty sure '99 was the changeover year. Many items are same for '01-'02. Some for a broader range. The body was the same from '99 to '05. I have checked the forums. I have mined for all the info I can use.

Not sure of the transfer case #.

I am wondering if the TCCM needs to be woken up at the dealer. It claimed it was already programmed, but some of these things need to be flashed or whatever to get the correct programming for the vehicle. I may do that before I throw any more parts at it.

Good news is that I was able to get my air bag light to go off by switching the PS to the 'on' position. And, put in a MAF sensor & dramatically improved my performance.

[ponchjoe]

I'm thinking your problem is the electronics in the transfer case. That is a very common problem especially early in the model run. There is also an update for the retaining ring eating into the case and causing an oil leak to that need to be looked for when it comes out.

[Deadhead]

So, take out the motor & replace next? Encoder ring going bad can cause this same code? Looks like you can just replace the ring.

[Formulabruce]

Wire from T case position switch to front axle solenoid can get damaged , cause and open, or shorted..