Random 4WD drive issues

[DocBrown]

Last winter my 4WD would not always engage. The selector light would flash and never engage then the "Service 4WD" light would come on. This was intermittent. Winter ended and I more or less forgot about. But I did change the transfer case fluid recently. I bought it with 85k and it's got 110k on now. I have no idea if the fluid was changed by previous owner. So I've been "exercising" the selector switch by putting it in 4WD and back to 2WD, then AWD and back to 2WD while parked. For the first couple of days I had the same behavior as over last winter. Then it started working normally and has for the past month as I occasionally test it.

This morning I tried it and it didn't work right away. I shut the truck off and started it again. It seemed to reset and recognize that it was still in 2WD. Or so I thought. I drove to work (23 miles) and as I pulled in the parking lot I could feel the binding, it was in 4WD. I looked at the selector and there was no lights. I parked, shut it off, started it and lights came back. Drove it around the lot and no binding. I'm worried I'm going to be going down the freeway and the 4WD just engages by itself, but what I'm beginning to think is that the 4WD was actually engaged the whole time and I never turned sharp enough to notice it. I did some searches but didn't find any info about whether or not it can change modes if the switch or something else fails. It seems to me that it would stay in 2WD if that's the mode it's in.

Could this just be a bad selector switch? It's cheap so I ordered one this morning from Rock Auto. Or should I be looking at something else?

EDIT: One additional thing, I'm going to disconnect the battery tonight as I have read in several thread that this can reset the switch.

 

[freddyboy61]

This does sound like a flaky selector switch (or an intermittent TCCM). Disconnecting the battery has no effect on "resetting" the switch, the switch is a dumb device. You're better off pulling the #8 fuse in the underhood fuse box to reset the TCCM if you need to.

 

[Mooseman]

Either the selector switch is done or the TCCM is. Although 02 was the year for bad TCCMs, Your might be an early 03 with the bad one. Maybe try to find both in a pick-a-part.

We can eliminate the disconnect and the TC/encoder motor because both would need to fail at the same time to cause the binding.

 

[DocBrown]

Thanks guys! You've given me some things to look at closer. Actually it's an '08 Sierra but the 4WD is pretty much exactly the same as the TBs, 4L60E trans, even looks to be the same transfer case, etc.

Regarding replacing the TCCM, isn't there some reprogramming that needs to be done by the dealer? I can't recall for sure...

 

[Sparky]

I do know that before I picked up my 07 Silverado the dealer had changed the switch due to an issue with it. I didn't notice it when I test drove the truck but the sales guy said it was intermittent and they were going to replace it. Could be the same problem you're having.

Just a side note though - the transfer case on these 07+ pickups do not have the same transfer case, and they do not use Autotrak II fluid. They actually use ATF, same Dex VI as the transmission. So if you put Autotrak in there, I'd get that drained and switched ASAP.

 

[DocBrown]

Thanks Sparky, nope I already knew it took DEX VI. It sure didn't look like a full 1.8 quarts drained out of it so that may have been part of the problem! Hopefully it's as simple as the selector switch.

 

[DocBrown]

Thought I'd update this in case anyone does a search in the future. It's been working fine for a while now. But the new selector switch did not fix the problem. I think 2 things happened. The previous owner likely never changed the TCF. It was low and the actuator got gummed up. So what it really took was a little time to work the actuator a bit and loosen it up. Thanks again for all the help!