That is how my 4wd works too. Try this - hit the button to engage 4Hi, then shift to park or neutral and shut the truck off. If when you restart the truck 4wd is engaged, then it is likely one of the two switches on the transfer case that read the shift position.

 

The 4lo issue is interesting, however the first part sounds like it could be the front actuator. All I do is drive in reverse long enough while trying to shift and that usually does that truck if it's actuator

 

I'm having a similar issue. If I try to engage 4HI several times it will eventually engage. How do I test the actuator to see if it is bad?

 

Ok, so I was wrong about 4-Lo. If I put the truck in 4-Lo the slow blinking light never stops, but I do get Lo-range, just not 4wd. The first time I tried that I must have gotten the fast blink, which means it isn't really trying to engage (sometimes it does that when I go 2-Hi- to 4-Low, I usually need to go to 4-Hi first and then 4-Lo).

The truck is a stick, if that matters. It won't finish engaging 4wd moving or stopped, or if I roll it forward and back. Is there a limit switch that tells the truck the t-case is finished so it can engage the front axle, or is this likely just a problem with the front axle actuator?

 

I'm still having this issue. Anyone know a way to test the front actuator? Don't want to spend the time and money if it may be something else.

 

Still trying to diagnose this issue. I've tried shifting into 4wd probably 40 times now and not once has it gone in. Moving, stopped, rolling backwards, nothing. Turning the truck on and off while shifting into 4wd, still nothing. Checked both fuses, the TCCM fuse and the FAXLE fuse, both are fine.

I found some instructions on testing the front actuator, and I don't *think* that's my issue but I could use a second opinion. I found that when I turn the truck on I get power at the pink wire at the actuator, which is correct. When I select either 4wd option I should be grounding the light blue wire, which is not happening. The light blue wire becoming grounded operates the actuator, right? Mine isn't being grounded, so more than likely the actuator is fine it just isn't being asked to engage.

So what can cause the light blue wire to not become grounded when I'm pushing the buttons for 4wd? Is this wire grounded directly by the dash buttons, or is it grounded by to TCCM? The truck windows don't leak, it's never been flooded, and the carpet is dry so I'd be surprised if the TCCM is actually bad but I guess you never know? What else can I do to diagnose or eliminate the TCCM since it's expensive?

Does anyone know if the TCCM waits until the t-case is finished shifting to actuate the front axle, or if it's done in parallel? If one of the t-case limit switches goes bad can it cause this?

 

Short of tracing down the wire's path in the schematics, I couldn't tell ya. I do believe those schematics are buried here somewhere if you want to give them a gander.

 

From those sounds of it, it shouldn't be a bad tccm, if that was the case, your 4wd would be fucked all together I'd think. Until you test with another one, I wouldn't rule it out completely. Is there anther member in your area that would allow you to plug his tccm into your truck?

Also, iirc, the tcase and actuator shift relatively simultaneously, my actuator usually takes longer to engage if it is.

 

So I found a schematic for the 4wd system wiring here:

https://www.2carpros.com/questions/...2005-chevrolet-colorado-4-wheel-drive-jumps-into-by-self-tire-noice-tires-makin

It's compressed and a bit hard to read, but since I already know what I'm looking at I can decipher it. The light-blue wire at the axle actuator goes to the TCCM. There is also a light-blue wire from the dash switch to the TCCM. What I'm not sure about is if the TCCM is actually interpreting the signal from the dash switch and internally grounding the wire to the axle actuator, or if the light-blue wire is just a pass through and the dash switch grounds the axle actuator directly.

Seems I could have a bad connection somewhere between the front axle actuator and the TCCM, the TCCM and the dash switch, or a bad TCCM?

Do I have to remove the driver's seat to access the TCCM?

 

I've set mine up where I don't have to pull the seat if I wanna finesse it a bit (I cut a hole in the carpet for easy access), but if it's your first time, you will have to. It's under the carpet and pulling the seat takes all of a couple minutes. Then a couple of the smaller plastic panels and peel the carpet back.

 

Pulled out the seat/carpet a couple days ago to get at the TCCM. No sign of water ever having been under the carpet, no apparent issues with the TCCM. I checked continuity of the light blue wire from the TCCM plug to the front axle actuator plug with a multimeter and it's good. That rules out a broken wire, so the TCCM is apparently just not commanding the front axle actuator. Could be a bad TCCM, although it is still operating the t-case properly. I'm thinking at this point it might be a bad limit switch in the t-case?

EDIT - Forgot to add that I tried leaving the truck battery disconnected, and I also left the TCCM unplugged overnight to see if I could reset any errors in the TCCM. That didn't work either, and I don't have any CEL's or service messages.

 

Turns out my issue was the switch in the t-case that reads 2wd/4wd. That's the switch that screws into the top for anyone with a similar issue.

 

Can you by any chance put up a picture of what it looks like or a diagram I think I have the same problem but do not know where to look

 

Thanks for the update. I am pretty certain that is my issue as well.