2002 Trailblazer Service 4WD light on can hear actuator but no shift into 4WD

[jbrozovich]

I had the 2002 Trailblazer TCCM problems with no light and and no shift. I replaced the TCCM with a used one and now the Service 4WD light comes on, the lights on the switch flash when I try to shift into 4wd and I can hear the actuator trying to shift but it won't shift into 4wd. What would be the logical next step?

Thanks
Jim B.

 

[The_Roadie]

There are two noises during the 2HI->A4WD transition: the front axle actuator (high pitched, 1 second) and the transfer case encoder motor (lower pitch, shorter duration).

During the A4WD->4HI transition, there is ONLY the encoder motor noise.

4LO is also the encoder motor, plus some internal gear noise from the transfer case.

Can you describe precisely what you see and hear during the 2HI->A4WD and also the A4WD->4HI mode transitions? (Don't jump two steps and do a 2HI->4HI transition yet.) Is the light steady on 2HI when you start the engine? Do all the mode lights flash during the lamp test time? How many miles do you have, and have you changed the transfer case fluid religiously every 50K?

 

[jbrozovich]

Thanks for your prompt response,

Answering your questions:
1) The TB has 135,000 miles.
2) The TCase fluid has not been replaced although Transmission and Radiator have been flushed twice.
3) The light is steady in 2HI
4) All lights on swithch flash a couple of seconds on start up then goes to steady 2HI
5) The sound I hear on 2HI to AWD is about a 1 second low pitched shhht sound.
6) I hear the same sound on 2HI to 4HI.

Thanks

Jim

 

[The_Roadie]

If you don't hear any high-pitched motor whine in the 2HI->A4WD transition, that's a dead front axle actuator. Could be electrical or mechanical. Aftermarket ones are available at parts stores or at the usual on-line places like Amazon and Rock Auto. Inspect the harness under the vehicle first. It's just in front of the passenger's side CV shaft.

You may also have congealed grease or a problem inside the splined disconnect that may show up when you get a working actuator and check functionality. Offroadtb.com Front Axle 4WD Disconnect

As to the deferred maintenance on the transfer case, I can't say much without adding a sense of urgency. The Owner's Manual is very clear about a 50K interval to replace the fluid. You must have had a good reason to put it off, but it's misplaced frugality. Use GM Auto Trac II fluid you get from the dealer. Some folks have ignored the fluid in there until 100K miles and then find they have a $2000 problem. Please hop on that issue ASAP, measure the fluid that comes out to see if it's low, and especially check its color.

 

[jbrozovich]

Thanks for the information. As far as deffered TCase oil change I must plead ignorance, the shop that does my oil changes never mentioned it and I didn't read the owners manual. I will get right on that.

Thanks

 

[The_Roadie]

Odd, but glad you found our community now. Most oil change places advice TOO MANY fluid changes rather than cluelessly staying silent. Your differentials are also overdue now. How about the other 100K maintenance, especially spark plugs?