Blazer would not previously go into 4wd, my mechanic rebuilt the transfer case with new chain, fork, bearings, etc. Now the 4wd works but it is stuck in 4wd. Of course he is on vacation, I called him and he said that its probably a vacuum problem. I did some online research and know about the vacuum actuator under the battery, and also there is some kind of switch on top of the transfer case. Anyone's guess which part it might be, or both? Both sound simple enough for me to replace by myself, only concern would be how the cable from vacuum actuator to front differential connects to the actuator- is that an easy on/off? One piece of history- prior to him fixing it, sometimes it would go into 4wd OK, other times it would not. The truck now stays in 4wd regardless if the 3-button panel 2hi/4hi/4lo is pushed to 2hi or 4hi- pressing a button causes that buttom to stay lit. I am afraid to try 4lo right now, would rather have it stuck in 4hi right now. I did physically inspect all the vacuum lines and they appear to be connected. Ideas? I'd like to fix it before he returns from vacation in the interest of having a fully-functional vehicle.

Thank-you!

 

I'm going to assume that you think the transfer case is engaged all the time? As for the actuator, its a very easy on off, there is a spring clip that holds the wire to the actuator, you just remove the clip from the groove and it slides right out.

 

Thank-you for the info, yes the transfer case and front wheels are engaged all the time, regardless if the pushbutton is set to 2Hi of 4Hi. Xfer case is NV233. So I should perhaps start by replacing the vacuum actuator?

- Dave

 

If the transfer case will not shift out of 4HI, the problem likely isn't with either the actuator under the battery nor the vacuum switch located on top of the transfer case. The transfer case activates the vacuum switch whenever it is in 4HI or 4LO so if the front axle is engaged, the system is working properly.

Have you removed the switch in the dash and tested the continuity on the appropriate terminals for each button? Maybe the switch isn't functioning properly. This would be my first stop in terms of diagnosing the issue given that you say that the light for 2HI doesn't even blink when you press 2HI. Maybe the switch itself is bad.

Wiring diagrams for the NV233 can be found in the Tech Article (DIY) section under error_401's post. The switch layout is given which is applicable for the 2nd gens, not the two button 1st gen switch.

 

The 2Hi and 4Hi lights both do work, when I press either one that light stays lit, but the truck remains locked in 4wd regardless of whether I press 2Hi and the 2Hi light is lit, or I press 4Hi and the 4Hi light is lit. Does that help clarify?

Thank-you!

 

How are you determining that the transfer case is still in 4HI?

If the 2HI light is lit, then the TCCM is getting a signal from the encoder motor that is telling it that it has completed the shift into 2HI.

 

Maybe I am incorrect, this is where I turn into a dummy and need some help.
I can press the 2Hi button, it lights up and it appears that I am in 4wd becuase the front wheels spin on ice. I press the 4Hi button, that button then lights up, and the front wheels also spin on ice, so it seems that the truck is stuck in 4wd regardless of whether the 2hi or 4hi button is pressed. Does that help clarify?

Thank-you for your expertise.

 

If the TCCM is lighting the 2HI light and power is still being directed to the front axle, then the transfer case was not reassembled properly.

 

OK, let me throw a curveball- I read tonight about resetting the TCCM by unplugging battery, so I disconnected battery cable for about an hour and reconnected. The truck cycled into / out of 4wd OK a few times, then stuck in 4wd again, no matter if the 2hi or 4hi button was pressed and stayed litup. I did manage to get it to stay in 2hi for now, and I am taking it to a different shop in the morning. One thing that may be noteworthy here- I live in MN, and it is awfully cold here- about 0 degrees right now, and this was the first time that I started the truck today. Prior to having the transfer case rebuilt, that was the symptom why I took it to the shop to begin with- it would not go into / out of 4wd, mostly it stayed in 2wd but occasionally I could get it to engage into 4wd, mostly when the engine was cold. Sound like a vacuum issue, or ?

 

IMO, the previous mechanic likely rebuilt the transfer case unnecessarily.

If it isn't shifting properly, then the problem is likely with the encoder motor and/or TCCM. The only way to know for sure is to start probing connections and monitoring the state of the encoder during attempted shifts. If the TCCM is getting a signal from the encoder motor that it has successfully shifted the transfer case into 2HI, but power is still being sent to the front axle, then the transfer case has an internal problem.