80K miles on this truck. pushbutton 4wd controls. Operates normally in Auto 4wd, 4Hi, and 4Lo, and 4wd functions as it should. By that I mean that the front wheel driveline is engaged in 4Hi & 4Lo, and engages under hard acceleration or rear-wheel slip in 4wd Auto. Here’s the problem: when I push the 2Hi button, it shifts into 2wd as it should whether moving or stationary. However, when I take the rig up to road speed in 2wd, it operates fine for a minute or two, but after I’ve slowed or stopped, it won’t move, and acts as if the transfer case has shifted into neutral. At times, it will move forward, but not in reverse for a short time before going neutral. Push the 4wd Auto button, and it goes back to working as it should in that mode. Transfer case is full of clean oil, wiring harness at transfer case (including ground) has been disassembled and inspected carefully. No codes nor “Service 4wd” messages are displayed. There is no clunking or grinding, and the actuator motor sounds as if it is working when the buttons are pushed with ignition on and engine not running. I have been unable to locate any fuse or fuses which might be associated with the transfer case or 4wd system.
I’m stumped. Anyone with similar problems, or potential solutions? THANKS!
I think yours might be similar to a trailblazer and one thing to check is the connections on the transmission itself.
No luck there. Any more ideas? Would a mechanic with a code reader be able to help me, even though there are no trouble codes displayed?
Have you checked the connections at the Transfer Case Control Module (TCCM), it was under the right kick panel on my 2000 Blazer. It wouldn’t hurt to disconnect the harness to reboot the TCCM.
Ed B.
I believe the TCCM is under the dash, lh side, behind the light switch according to my Chilton’s manual. Partial disassembly of the dash is required to access, and, to answer your question, I haven’t yet gone there…
Ok, I’ve gotten to the point where I can at least see the TCCM. Please tell me more about unplugging and rebooting. There are several harnesses and bookoo wires plugged into the thing. I’m a bit nervous while working in close proximity to the airbag system, etc. What harness would I unplug? Key off or on? Would disconnecting the battery serve the same purpose?
Wiring at the TCCM appears fine. Competent mechanic is unable to pull any trouble codes. Chilton’s manual is no help. C’mon CarTalk guys… can someone help me out with advice? 
Switches fail quite often on these trucks. They also can place the transfer case into neutral for flat towing by pressing 2 buttons together. Maybe the switch has failed and is commanding the t-case into neutral thus not setting any codes. The t-case thinks you want neutral. They are cheap and easy to replace. It can’t hurt to swap it out because it is going to fail fairly soon anyway and that may fix your problem. If that doesn’t work, the shift actuator’s internal sensor may be failing to register 2WD. Good luck, let us know if that helps. BTW, watch for t-case oil leaks, a hardened wear washer tends to wear through the rear case cause a very hard to find leak.
Did you get the transfer case oil from a dealer? Have you replaced the rear differential fluid? The reason I ask about the rear is you need to put an additive in or buy the expensive stuff from the dealer.
Mustang, my switch seems to work like it should. I can put it in neutral by holding 2h and 4l simultaneously for 10 seconds, it goes to neutral and the neutral light comes on, and it shifts as it should otherwise into and out of all the ranges. However, the neutral light does not illuminate when driving in 2h, rather the 2h indicator remains lit even after the truck acts as if it has gone to neutral. Chilton’s manual tells me that there is a lock in the system that is supposed to keep it in the selected gear (unless auto4wd is selected), but doesn’t tell me if the lock is part of the motor? actuator? sensor? or how to isolate or test it. Yes, I’ve been told that these cases can get holes worn in them from the inside out, I hear ya. I’m planning to sell this truck soon, but would like to fix it first…
My switch looked like it worked properly, too, but kept throwing a “service AWD” on the dash. The lights are wired directly to the switch, not to the T-case so throwing the switch lights the light but you don’t know for sure what is actually being commanded of the T-case. They are cheap and very easy to replace. The dash panel it sits in just snaps off, a couple of screws and a connector and you are there.
I’ve had my instrument panel apart in order to check connections on the switch as well as the tccm, and I know how easily the switch can be replaced at a cost of only ~$16. Unlike you, I have never had a “service AWD” light. My TC goes into 2wd as it should, but doesn’t stay there. There is a “motor lock” as part of the system, but I’ve had no luck finding out how to locate, diagnose, service, or replace the lock. Some of these tc’s have a detent pawl and spring to keep them in gear, I’m told. I’m quite hesitant to tear into the thing without knowing wtf to look for, nor do I want to pay an admittedly clueless shhmuck at the Chevy dealer $80/hr to do the same… I’m thinking that I might sell this pickup to someone who wants to leave it in Auto4wd until it goes seriously haywire. I’ve recently bought a real truck (Duramax/Allison), and this half-ton is just taking up space in my garage.
I’m back. Sold the truck to an acquaintance with full understanding and disclosure of issues. He said he could fix it and I wished him luck… Last time we visited, he had replaced the switch to no avail. I will post here if and when I learn more.
My 4WD trucks all have 2 levers sticking up through the floorboard. 4 positions…2H-N-4H-4L . The front hubs have a dial, “IN & Out”…This system never fails…
At ldl3 was the issue ever resolved my 2006 is doing same thing
Was issue ever resolved my 2006 is doing same thing
Talked with current owner today. He ultimately resolved the issue by replacing the ”module (or modulator) on the transfer case”, at a cost of $300+ for parts plus $50 for labor done by an acquaintance. He has since driven 10K+ miles w/o further issues.
