My 'Old Faithful" 2001 LT has begun to have some aches and pains. I don't seem to be getting any control of the FWD functions, and all the fuses check out OK, so I thought I'd check out the 4 button dashboard switch.
I don't seem to be getting power to it, but since it's a mix of ignition hot, computer signals, and connection to the Auto FWD controller, I am hoping someone has a pinout of the actual switch. I have a diagram, but it isn't clear to me which pin controls what.
Does anyone have one?
Thanks.

 

Know that the transfer case control modules (TCCMs) can fail. Also vacuum leaks in the hoses in the engine compartment that supply vacuum to engage the front axle can leak.

However, attached are the schematics for a 1999 4-button transfer case select switch. They might help.

 

Do the buttons light up? That is where you need to start. All three buttons should illuminate for a few seconds when the key is turned to "on," then the currently selected mode button should stay lit.

 

Thanks, christine_208. If I read this right, the hot wire going to the 4 button switch is supposed to be brown from the Hot in Run fuse. The closest I have in my harness is a tan wire. I don't have a brown. I'll check it and see if it has any effect.
Thanks, again.
ed9213

 

Thanks, BlazermanWI. The lights do not come on, and the fuses are good. Once I isolate the hot wire, I'll be able to tell if it's just a burned out switch.
Thanks, again.
ed9213

 

Thanks, again, christine_208. The hot wire is brown and comes in through the smaller of the two connectors on the back of the switch. All seems OK there, so it must be a burned out switch. Your diagram was the key. Thanks. ed9213

 

Before tossing the switch out, try re-soldering all the pins on the connector. Have found that cracked solder joints are the cause of many problems.

 

Thanks, LannyL81. I'll give that a try later today.
ed9213

 

4WD switches don't typically give many problems. Here's some specific info for the 2001 4-button system.

Did you check the ATC fuse in the under the hold relay center? There are multiple fuses for the 4WD system. ATC is the main fuse that powers the TCCM and the encoder motor. Without it, you get nothing.

TCCM supplies an 8V reference signal to the switch. Depending on which button you push a different voltage is returned back to the TCCM and it will attempt to move the encoder motor and transfer case to the appropriate position. This is the primary 4WD control circuit. Front axle locking in is separate.

The brown wire you speak of only powers the lights in the buttons of the switch - and they will never light up or flash until the TCCM is happy decides to provide a ground for the individual circuits for the lights. TCCM no worky - then no lights in buttons.

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

A common problem is the power connection (big red wire) at the TCCM gets corroded and does not make a good connection. Sometimes cleaning this can cure 4WD issues - certainly it is one of the first things to check. Often the encoder motor burns up and blows the ATC fuse. Keep in mind that since the power for the encoder motor passes through the TCCM, it can be damaged as well. Switches are typically pretty trouble free.

If you end up needing a replacement TCCM, know that they are programmed with info specific to your vehicle. GM ones do not come pre-programmed. Cardone units do. Note this statement is apparently wrong. See next post.

good luck and best wishes for a successful repair.

 

Sorry to interject and slightly high-jack this thread but perhaps the answer to my question could be considered relevant to this discussion and would be one from which others would benefit.

Lesmeyer, I replaced my TCCM last year with a NOS GM TCCM with a part number appropriate for my year, model and type of system (4-button). Should I have done something to program it? It seems to be operating just fine for me.