Typical 4wd question

[studedude]

So here we go. 2002 Trailblazer with some 4wd problems. Would not shift into any 4wd mode. Codes were pulled, they are: C0300 C0306 C0550 B2725.
What has been done so far. Replaced fuse #8, Changed t-case fluid, this has been done fairly regularly. Used TCCM from 03 Envoy with same gear ratio.
New actuator motor, old one was bad. Known good switch was switched in. Now I have 4hi and it works well. A4WD engages but upon wheel slip all lights on switch flash
and no A4WD. When I shift to 4lo I hear the actuator working but it wont go into 4lo. Yes, it is in neutral. What do you guys think?

 

[The_Roadie]

Encoder motor immediately springs to mind. You can probably swap it with an aftermarket unit cheaper than paying a dealer to run the transfer case through its paces with their Tech II tool. Normally, road conditions are not the specific ones that A4WD will help with, so it's not worth the risk of abrupt engagement to even use that mode except for testing.

Assume you mean front axle actuator was replaced because it was bad. The actuator is on the splined disconnect, and only makes noise in 2HI->A4WD transitions and vice versa. The transfer case encoder motor is the one that makes noise in EVERY possible mode transition including 4HI->4LO.

When the transfer case fails to go into 4LO, what is the behavior of the lights on the switch? Does it blink on 4LO and go steady on 4HI, or does it go steady on 4LO but not actually give you LO range?

You had a lot of stuff replaced on that puppy.

 

[studedude]

Sorry, it was the encoder motor that I replaced not the actuator $120.00 new. I had the actuator on my mind, but since 4Hi works I think the actuator is OK.
When shifting from 4Hi to 4Lo the 4Lo light blinks and it goes back to 4hi steady. I can hear the encoder trying to shift to 4Lo but no go.
Yeah I replaced a lot of stuff but had a donor truck to use for some. I don't like A4WD much but its my wifes Trailblazer and she probably uses it.

 

[The_Roadie]

Could be a mechanical issue inside the transfer case, then.

 

[studedude]

The c0300 code is for the rear speed sensor, could a defective speed sensor prevent 4LO from engaging?

 

[The_Roadie]

Hmmmmm, I suppose it could. The interlock in the TCCM is looking for a low speed, but a dead sensor should be interpreted as zero MPH, I would have guessed. I'm on a business trip without my manuals to check for sure. Ten minutes with a competent tech with a Tech II tool could tell you for certain. You could call around and see if there are any independent mechanics with a suitable scan tool.

 

[studedude]

I know a guy that can do this. I will check with him some time this week. Thanks for the input.