I see a lot of threads about this, but I don't want to spend money buying each part and not solve the problem and waste money.


So my situation is...Vehicle is stuck in 4x4, I have the Auto-Trac (4 button switch) and all the lights are lit up. So to get my vehicle out of 4x4, I've been taking out the 4x4 fuse in the drivers side dash. This is frustrating because I guess this fuse also controls the Gas gauge and some other electronics on the dash. So its always showing I have no gas and low gas light is always on. Then I put the fuse back in and im back in 4x4 and all the lights are lit up next too each button.


So if any of you have the time can you tell me what to check in which order and how to check it?


I know the causes can be:


TCCM (located behind the passenger kick panel) I've heard this can lock up, and I also read somewhere this can be reset? If so how?


The Auto-Trac 4 button switch can be bad and might need to be replaced.


The Vacuum Actuator located under the battery tray could be bad or the vacuum lines themselves could be rotted.


The Electronic vacuum solenoid located by the distributer could be bad and need to be replaced.


So where should I start and how do I check each of these items to see if there good or not? I really don't want to waste money if possible.


Thanks so much for the help. Love this forum.

 

I actually just found Hanr3 post on the sticky and it explains a lot about 4x4 problems. It seems to explain a lot so this may help

 

So after reading the sticky I guess I onley have 2 questions left.














The Electronic vacuum solenoid located by the distributer. What is the name or part number for this item? cannot find it online.


And how do I test the TCCM to see if this is bad or not?


I think his thread explains just about everything else. Thanks!

 

So far I've removed the passenger kick panel, TCCM looked fine, cleaned it up and put it back in. Removed the 4 button switch and checked it out. it looked fine and as I said above all the lights are lit up and wont go off so I don't think the switch is the problem. Next Im going to check the transfer case and see how the fluid is. Only GM carries the t-case fluid I need so will be running by there today to get it. I also forgot to mention when I do put the fuse in and im in 4wd. when I press any of the buttons (auto4, 4hi, 4 low and 2 hi) there is no response from anything. I don't hear anything at all

 

Thank you for your service!


Have you checked all 4 fuses? Check both terminals of each fuse, do not remove the fuse from the fuse panel while testing.



In the underhood fuse panel:
10amp CRANK fuse must show battery voltage in the START position of the ignition switch.
20amp ATC fuse must show battery voltage at all times.


In the instrument panel fuse panel:
4WD 10amp fuse #15 must show battery voltage with ignition in the RUN position.
GUAGES 10amp fuse #4 must show battery voltage in RUN and START positions of the ignition switch.


Post your results.

 

The fact that you can disconnect the front axle by pulling the fuse effectively tests the solenoid that you refer to.

4-button 4WD reqires a capable scan tool to communicate with the TCCM for diagnosis using factory dagnostic charts. This is the only way to avoid guesswork.

Alternatively, I posted some time ago about using an OBD2 terminal and typing in the binary to communicate with TCCM to simply retrieve codes and to reset the TCCM.

If lights are all lit but don't flash when you push a control button and nothing moves and the 20A ATC fuse doesn't blow, then I would suspect the TCCM. But other things can be bad as well (cascading problems). Mine had both a bad TCCM and a bad encoder motor $$$$$$$ (shorted encoder motor apparently took out the TCCM and was blowing the 20A fuse). Note that all current for the encoder motor goes directly through the TCCM.

Good luck, these can be difficult and quite frustrating to do without the Tech2.

Makes you wish for a 4wd lever on the floor. It's kind of like controls for modern heater air blend doors. A simple cable or lever was replaced by electronic switches, modules, programmers and motors. This is the price you pay to have anything automatically electronically controlled. Not sure if anything was actually improved - certainly not reliability.

Les

 

I did not check the fuses. Will buy A 12 volt test light when I get off work, and new fuses (there cheap so might aswell).


Thanks for reply will post results today

 

Just did the test. 20 amp ATC fuse checked out good in all positions. 10 amp crank fuse did not read start position. 4wd fuse checked out good in run position. 10 amp gauge fuse worked in RUN position but did not work in START position.

 

The CRANK fuse, did it show voltage on only one terminal of the fuse?

 

Let me check again to be 100%. Just to clarify, START is just putting the keys in the ignition and you hear the beeping sound, and RUN is the position right before you crank the car correct?