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2004 chevy trailblazer_lt
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Discussion Starter · #1 ·
Huh... the "similar threads" popup is kinda neat - didn't find my issue though.

Anyway, I replaced my encoder motor back in February, which solved my problems at the time. I had been stuck in 4WD, after the replacement all trans modes were available once more.

Changed the oil this weekend and decided to exercise the system once more. Wifey has been running in A4WD, no biggy - but I can't get a solid lock into any other modes now.

What I mean is this: Ignition off, switching from A4WD to 2HI results in the light flashing and the encoder motor whining away... it sounds like it cycles 4 times trying to do it's thing before stopping. The A4WD light remains lit, no other changes noted. Same thing happens if I switch from A4WD to 4HI (flashing light, encoder motor chugging away for 4 cycles, then nothing with the A4WD remaining lit). At least the TB drives like it's locked in 2WD this time.

I've pulled #8 and #48 fuses, which didn't do anything (I didn't expect it to). I got underneath and didn't find any evidence of leaks at the transfer case. The input shaft to the rear diff DOES show a leak though, which I expected to see somthing because of the few drips I've found in the garage lately - a spot that amounted to about 1" diameter on the floor.

Sorry for the long initial post, I've searched around again and didn't see anything that appeared related. I don't think it's the switch itself, nor do I think it's the encoder motor. Maybe the encoder sensor - is there a way to test that?

Here's my guilty admission... the TB has about 110k miles on it and I've never serviced the diffs or the transfer case. Yes that's on my list of important things to do, just mentioning it in the interest of full disclosure.

Ideas? Some things to look for?
Thanks,
-Andy
 

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2004 chevy trailblazer_lt
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Search for front axle actuator.

Your truck has both an encoder motor under the left side of the dash and a front axle actuator on the side of the transfer case. They make two different sounds when engaging (or attempting to engage.)

Front axle actuators lead a hard, dirty, hot and tough life attached to the transfer case, and is the first suspect in any engagement problem.

Try 'exercising' the switch through all modes 40 or 50 times, and listen for the two distinct noises.

There are great threads in here and what to listen for.

Actuators seem to need 'exercising' on a regular basis or it gets slow from stiff grease or corrosion on the printed circuit electrical contacts on the inside.
 

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Discussion Starter · #3 ·
Thanks for the advise. While I can't write off the actuator as the problem (or even as A problem), I think this may have more to do with the transfer case. I'm a little concerned that it's internal there, maybe something binding - although it's never been open and there is no evidence of fluid leaking. When I operate the switch I have time to jump underneath and I can feel the encoder motor vibrating slightly with its efforts. That's how I know it's the encoder motor cycling though.

Now why it's cycling and not completing the mode change - I don't know. I don't have enough experience to speculate. I've read through a ton of posts though, which has me to the point that I don't think it's the switch (since the rest of the system is trying to do something when I operate the switch).

Maybe the actuator isn't getting energized, and that somehow has something to do with the encoder cycling? I don't know.

Thanks though...
-Andy
 

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Discussion Starter · #4 ·
Here's maybe another clue, I don't hear anything from the actuator up front while the encoder motor is cycling.

What order do these things operate in? What I mean is... does the encoder motor go, then the actuator - or maybe the actuator is dead and so the encoder won't finish it's task?

Advice?
-Andy
 

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2004 gmc
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The front axle actuator and the TC encoder motor are entirely separate and success or failure of one won't affect the other one. Except if either one fails to move as commanded, the TCCM gives up and flashes the Service 4WD light.

When one of them fails, and the TCCM gives up, you usually need to pull the fuse to reset it and get it to try again.

The actuator only operates on the 2WD->A4WD mode transition and vice versa, and it's a higher pitched whine than the encoder motor. The encoder motor moves a little bit on every possible mode transition.

The actuator can get greased up on the feedback sensor side or the motor drive sliding contacts. I posted a disassembly and rebuild thread about how to fix one without buying a new one. You might remove two bolts and take the actuator out and see if it works in free air.

If you have a feedback sensor problem, and have a meter and know how to use it, I can talk you through poking at the connector on the TCCM behind the dash to troubleshoot it further.
 

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Discussion Starter · #6 ·
Thanks roadie... I don't have a "Service 4WD" light - not yet anyway. Every time I hit the switch it (the encoder) tries to do something. I'm going to try pull the actator to see if I can get it to operate off-vehicle as you suggest. I can't tell if it's trying or not right now, the encoder is making enough of a racket.

I found your actuator disassembly thread here (for others reference):
http://forums.trailvoy.com/showthread.php?t=46356

I do have a DMM, and I do know how to use it if we get to that point.

I do also need to get some fluids ordered so I can do some maintenance on this vehicle before it's too late.

-Andy
 

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Discussion Starter · #7 · (Edited)
I wimped out and took it to a dealer to diagnose my problem.

The tech go it to spit out a code pointing to failure in the transfer case itself. He pulled the encoder motor off, and showed me how the splined shaft could now easily be turned by hand (it can turn maybe 1/8 of a rotation). He said that shouldn't happen at all.

He was thinking blown clutch packs, could be other internals as well. The recommendation was replace the TC.

How hard is that, can I put the TB up on ramps in my garage and pull it off?

Also - any thoughts on where I can find one of the "updated" TC's... and is there a way I can tell that it's an updated one? I know I'm looking for a NVG-226 (RPO code NP8)... does anyone have a GM part number for that - maybe the updated version has a different number?

I went to GMPartsDirect (the catalog on there), and it spit out 4 different TC's when I called up a 2004 4WD TB.

Yes... it's been driven mostly in A4WD

THANKS!
-Andy
 

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I would get one off Ebay, or www.car-parts.com and find an acceptably nearby junkyard with one from your year or newer. Sorry to hear.

You might find more details about the part numbers by drilling down at www.compnine.com, but I haven't heard anything about an "updated" TC.

Why would you run around mostly in A4WD? Excessive and unnecessary clutch wear, combined with not changing the fluid every 50K, for very little drivability benefit?
 

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Discussion Starter · #9 · (Edited)
Thanks Bill... I'll see what I can find on ebay and in the bone yards. I read up a bit on pulling out a TC, and it doesn't look too bad. I'll know more after I get into it though.

By "updated", I was talking about the "New Improved Transfer Case" mentioned in this thread -
New Transfer Case
The part number in THAT thread is 24242561.

You know... I've come across a couple of online catalogs that list an "NVG-266C". That came up in another thread I read earlier today, the "C". You said in that one (IIRC it was you) that you hadn't heard of a "C" on these. I just wonder if that is a way to tell if it's one of the "New Improved" ones? Like I said, you look up a TC for a 2004 4WD TB and you get a list of 4 or 5... and that "C" is one of them.

I just checked on the "Comp Nine" link you gave, got down to the TC diagram and they refer to it as "2004-2008 T1 Transfer Case (NVG 226C)(NP8)". They call that PN 24228408.

I admit, I pay a lot more attention to the car than the TB - and so now I'm paying for the neglect. Wife drives it in A4WD because that's what the shop told her to do, and I didn't know any better. We won't be doing that anymore.

I've changed the fluids by now (FWIW), actually shortly after my 6/12 post. Now I need to look into some end links for the rear sway bar, getting some "thudding" back there over bumps and they seem to have more movement than I'd expect.
 
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