Have a 1999 Blazer (trailblazer package). It is stuck in 4 auto.

I have:
Checked/replace vacuum lines in engine bay.
Replace dash switch (4 button).
Disconnected and cleaned the connection to the TCCM behind the passenger kick panel.

What else should I look into? I have one connection on the orange connector going into the TCCM ( This is post 1 on he connector) Not sure if it's making good contact to the TCCM. Thinking of soldering a wire to the back of the plug in the TCCM and jumping this wire but can anyone tell me what the wires are for on this connector?

Anything else I can look into?

If I pull the vacuum line to the diaphragm going under the battery box, will this disengage the front axle while I try to pin point my issue? This is just a winter car and I really don't want to drive my Duramax in this thick layer of salt they have layer on the roads.

 

yep , disconnect it at the solenoid on the firewall near the distributor for troubleshooting.

got this from the manual

Do you have access to a real good scanner ? , That system may have a code stored to help you diagnose.

 

No I don't. My buddy use to work at the Chevy dealer but has since took a different job.

All I have is and Edge Insight for reading codes/gauges on my duramax.

 

Ok. Disconnect the solenoid at the firewall. Then the auto 4wd button/light started hyperflashing. Put it in gear and the 2hi light came on and the 4 auto button turned off. Plug it back in and it goes right back to 4 auto with out hitting the button.

Although the inside of the TCCM looks really clean, could it still be bad?

 

Sure, its possible. without reading codes you could just be guessing and throwing parts at it. Unfortunately....if you had spare good parts it would help , but I would recommend checking for codes as your starting point. There is a lot of good trouble shooting info on this site , just don't get the 3 and 4 button systems mixed up while trouble shooting....but you will have a bit of reading to do.

 

What do you mean by stuck? What exactly are your observations with lights in the controls, and do they flash or not when you select a different mode?

Did you find corrosion at the TCCM? which wire?

wiring schematic and much more is here

https://blazerforum.com/forum/2nd-ge...-blazer-89044/

 

It will not shift or attempt to shift at all. When you select any button, it does nothing. No flashing , no clicking from the TCCM, no noise from the motor on the t-case.

Yes, I found corrosion at both plugs. Tried to clean them the best I could using a heavy duty electrical cleaner and dielectric grease after. I'm thinking the one plug circled below might not be making contact. It looks like it might be too corroded away to contact the plug on the TCCM side.

The orange connector - corrosion at the tan wire

The black connector - corrosion at the orange wire.

I'm thinking of soldering a wire to the back of the TCCM on this tan wire and splicing it into the harness to see if it works then but I really don't like hacking up the factor harness.





Other then this transfer case issue, its been a great truck. All this electrical issues is why I made sure my Tahoe and Silverado both came with the floor shift t-case.

 

Check the fuses ATC under the hood and 4WD in the fuse block on the left side of the dash if you are getting no lights in the display. Otherwise it still may be a bad connection (or worst case a bad TCCM from the bad connection)

 

Just went out to check, both those fuses are still good. Guess ill start by trying to jump that bad pin on the TCCM and go from there. Also will start looking for a TCCM for the 4auto (seems to be hard to find used). Thanks for all the help.

 

If you are not getting any lights at all in the 4WD display when you first start the vehicle, then it is most likely because the TCCM is not returning any status lights to the controls. Probable causes are power to the TCCM, the TCCM itself, and corrosion on the TCCM connectors. I think you are on the right track, but I would repair the connectors using wires from a junk vehicle if they are too far gone. Figure out how to release the terminals from the connectors, and then you can replace the bad terminal using a section of (junkyard) wire with the terminal crimped in place. You can solder it to the old wire a few inches up the line after cutting off the offending terminal.

If you end up replacing the TCCM, I would forget the used junk. I recommend a Cardone unit drop shipped from the manufacturer by Summit Racing. They will price match to any price you can find on the Internet (you have to call them), they have fast free shipping on something this price, and a GREAT return policy. If for some reason it doesn't fix your problem, just return it. Might cost you shipping, but you get a return package label as part of your receipt..