I have a 98 GMC Jimmy 4x4 that is now stuck in 4lo. I used it without any problems switching from 2 to 4 hi or lo till yesterday. I had to move a heavy boat out of a muddy hole and to save effort on the trainy I shifted to 4 Lo. I then hooked up to the boat, moved it to where I needed and dropped it. But when I went to shift out of 4 LO to either 4 HI or 2 HI, no go. In neutral the lights flash as I press the switch, then nothing. In any other gear P-r-d-1-2, it will change to a flashing light on the position selected, but never engages and eventually sets back to 4 LO. I have tried backing up, rolling forward slowly, dead stop, and even driveing at a crawl to disengage it. No luck. As a desperate attempt I looked at the transfer vaccum switch and found it full of fluid and stuck open. I replaced it and nothing has changed. Still does not even try to change from 4 LO to anything else. I have the 3 button electric shift on the dash. Anyone who can tell me what I need to look at next? I've read all the posts around this topic so far and none seem to hit my particular problem exactly. What controls the range selection, can I check this, and where is it? What is a TCCM? It also seems to be stuck in 4W. I am guessing that is controled the same as the range by the switch somehow, but do not really know how this thing works.

Start with this one by Muddog.
http://www.automotiveforums.com/vbulletin/showthread.php?t=572914

If a 233 transfer case you should be able to ground pin 13 on your diagnostic connector and get codes.
If any codes post back.

Look over all wiring and fuses and vacuum.

4W low and 4W high and 2W is shifted by the encoder motor on transfer case.

Can you hear the motor move when you hit the push buttons?
Is the motor wires good and getting power?
The push buttons tells the transfer case computer/tccm to shift the motor and the motor changes the transfer case.

The vacuum part is for locking the front axle in and out.

I appreciate the quick responce. The only noise heard is the push button part. I don't hear any clicking or motor or anything. It acts like nothing is ever being switched or even trying to. It is as if the button was never pushed. It just continues on without any indication of trying to change to any other setting. I checked all the wires and vaccum lines. That is what led me to the switch I replaced. I had oil in the vaccum line. That probable will explain my problem with the A/C system as well. No mode control on it as per one of the previous threads. I am the only one around, so any 2 man work like checking for signals when activated and stuff like that I have to fogo for now.

I believe it is the 233, NP or NV I don't know, but the description I read from earlier posts seem to fit the one I have.

Check for codes.
And post back code no.
MT

OK I will check that out tonight. A quick question. What does removing the battery cable have to do with all this? I've seen this in a bunch of different posts and am wondering is there something I can reset by doing this that may in fact fix this? Also is the ground a chassis ground or a case ground, or does it matter, and do I understand correctly that the flashing of the 4x4 push buttons on the dash is where it will be displayed?

Check for codes.
And post back codes.
Codes will be flashed on shift button lights.
Is all button lights coming on for a bulb check when key is first turned on?
Then what are they doing after engine is started?

The cable disconnect reboots the PCM and TCCM after code check give it a try.
But disconnect neg first and hook it up last or you may do more than reboot it.

I have a 98 GMC Jimmy 4x4 that is now stuck in 4lo. I used it without any problems switching from 2 to 4 hi or lo till yesterday. I had to move a heavy boat out of a muddy hole and to save effort on the trainy I shifted to 4 Lo. I then hooked up to the boat, moved it to where I needed and dropped it. But when I went to shift out of 4 LO to either 4 HI or 2 HI, no go. In neutral the lights flash as I press the switch, then nothing. In any other gear P-r-d-1-2, it will change to a flashing light on the position selected, but never engages and eventually sets back to 4 LO. I have tried backing up, rolling forward slowly, dead stop, and even driveing at a crawl to disengage it. No luck. As a desperate attempt I looked at the transfer vaccum switch and found it full of fluid and stuck open. I replaced it and nothing has changed. Still does not even try to change from 4 LO to anything else. I have the 3 button electric shift on the dash. Anyone who can tell me what I need to look at next? I've read all the posts around this topic so far and none seem to hit my particular problem exactly. What controls the range selection, can I check this, and where is it? What is a TCCM? It also seems to be stuck in 4W. I am guessing that is controled the same as the range by the switch somehow, but do not really know how this thing works.
I had this problem on my 96 Blazer and it turned out to be the push button switch. The plastic welds on the plastic button hinge broke lose and wedged the contacts closed all the time. I just glued it back into postion and it worked.

OK. Here goes. I found the critter and grounded the pin which did absolutely nothing. No codes no change. I disconnected the battery for about an hour. When I plugged it back up I had a change in operation. When I pressed the buttons to change ranges it would light up that selected range and flash, but still never select it then fall back to 4 LO. While it was flashing the box was clicking. It sounded like it would click to try to select the new range, but never do anything. then it would click again just before it would set back to 4 LO. After a few tries at this and going through the routine of backing up, moving forward and any other combination I could dream up at the time, it would stop clicking at all. Everytime I rebooted the thing this would happen, but nothing ever moved, no switch out of 4x4, no moving of the motor to change ranges. When i checked the lights, all work. When I start the car they go to the bulb check and straight to 4 LO. No flashing, blinking, or any sign of wanting to do anything else. I tried putting it in neutral by pressing 2 HI and 4 LO at once as the book said and that didn't do anything either. Any more suggestions? At this point I am completely clueless.

I did find a vacuum leak in the A/C system. I was hunting down the switch and oil problem and found a diconnected connector for the vacuum controller at the dash. Did not affect the 4x4 at all though. All other wires and lines checked good.

What transfer case?
What does the tag on the back of it say?

I will check it tonight to be sure, but I believe it is a NP233.

If a 233 it should flash a code on shift button lights.
When key is first turned on what do the shift button lights do?

All it does is give me the bulb check. All lights come on, then eventually go out to just the 4 LO button being lit.

It should be setting a code.
Rerun the code check and wach the shift button lights.
Check all fuses and wiring and power feeds.

I would suggest a factory service manual or one of these for testing and getting to the problem.
http://www.alldata.com/products/diy/index.html

They both have a repair flow chart.
But it is sometimes a long and drawned out check procedure.
Depending on codes and the shift button light and what it is doing or not doing.
But in the end it will lead you to the problem.

If you can get a code post back code no.
The 233 will only gives 4 codes
Code 1 or 2 or 3 or 4.
Good luck MT

Well I am back on the road with a temp fix. I removed the encoder motor and tried to run it from one range to the other by pushing the buttons. Same results. TCCM clicks like it is trying, the motor doesn't budge, and the button lights indicate the 4LO range still. I manually changed the transfer case to 2 HI, then set the encoder motor to match the keyway position, then reassembled everything. Now the buttons indicate 2HI and it is in 2HI, but it still will not change and there is no codes being given at all. I have 2HI so I can drive, but I still am not sure what the original problem is. I am inclined to believe the encoder motor is the problem since it doesn't even try to move. Any more suggestions. The wiring all checked out and I haven't been able to get a hold of anything to show actual signals and timings for the TCCM, yet.

Had the same problem on my 98. The problem is with an electronic box hidden behind the passenger side kick panel. If you open the passenger side door and pull off the passenger side kick panel there will be an electronic box behind it which controls your 4X4 functions. What I have to do to mine is unplug the electronic connector going into the box. For some reason this has to be done with the ignition key in the on position. Then plug it back in with the ignition key on. Try pushing the 4X4 HI LOW buttons and you should hear the drive shaft engaging in the HI and LOW positions.

Thanks. I'll try that tonight. I'll let you know how it goes.