Ok, so I read all I could about 4 x 4 problems. My 97 Jimmy with the NV233 transfer case will not shift into 4 Lo. It will shift fine in 4 Hi and 2 Hi although I found only today that in 2wd, the front dif. is still engaged but the transfer case is in 2wd mode. The vacuum actuator under the battery does not release. I grounded pin 13 of the DLC and no codes appear. I am guessing the vacuum switch on the transfer case is bad and allowing vacuum as soon as the engine is running regardless of what mode it is in. It eventually bleeds off after a while of not running because I can turn the front drive shaft by hand. I ordered a new one and should get it tomorrow. Now, from what I was reading, if the encoder motor was bad, it would shift in 4 lo but not 4 hi. Could the vacuum switch keep it from shifting in 4 lo or should I be looking for something else? I am getting awfully tired of pouring $$ into this pit.
Don

 

Please describe in detail exactly how you determined:

1. TC shifts fine between 4hi and 2Hi, but not into 4Lo. And what about neutral? What do the indicator lights do. Any noises occur?
2. In 2wd, the front dif. is still engaged but the transfer case is in 2wd mode

Just getting the background info to help you.

 

When I push the 4 lo dash button, the light goes out and the 4 hi light comes on. No noise till the 4hi light comes on. I determined everything was ok by spinning the wheels under power in gravel. The 2hi would spin all day while 4 hi would grab and go. All lights work ok except 4 lo. Neutral!!! I can put the shifter in neutral but nothing changes.


First, I tried turning the front driveshaft by hand. When it is left sitting all night in 2wd and park, I can easily turn it by hand. As soon as I start the truc, it locks.
Second, the vacuum actuator under the battery tray is completely retracted.
Don

 

Here is the 233 transfer case factory wiring diagrams and trouble code charts. You may want to go through the read codes procedure and note if all lights flash once and that you are grounding the term before turning the ignition on.

https://blazerforum.com/forum/2nd-ge...-blazer-89670/

Disconnect the connector from the TCCM and inspect wire terminals for corrosion. This is a typical problem.

If no codes and electronics seem normal the first question I have is if the TC itself will go through its different ranges and be functional. Take the encoder motor off and disconnect it and the TCCM (don't plug it in when encoder motor not on the transfer case) and see if you can switch between 2Hi/4Hi/4Lo using a wrench on the shaft. Shouldn't be too difficult to click through the positions but you might have to jack up both fronts and one rear wheel well as put trans in neutral so no bind in TC when going into/out of 4lo. You can then start the vehicle and drive in each position to see if it is fully operable (forgot 233 apparently does not have a neutral). You should not have vacuum when in 2WD. if you do, either the switch is bad or the TC is not fully going into 2WD. if the 2wd position click with the wrench is good, then I would assume TC is fully in 2WD and its a bad vacuum switch causing the front axle to stay engaged. I don't see how the vacuum switch could keep the TC from shifting fully.

If all of this check out good, then we will go from there.

 

Thanks' Les. I just finished putting in the new switch. The ball on the old one is stuck in the switch. Now the front axle disengages but, I have another problem. None of the 4X4 ranges work. When I push on the 4hi or lo, the lights flash 4 to 5 times and then it reverts to 2wd. I am wondering if I installed the vacuum lines wrong. I took out the 4wd fuse for now to try and reset the TCCM. If none of this works, I will do the above listed procedures. It's pouring like crazy and I work in my driveway so, I guess I will call it a day.
Don
PS- I reset the TCCM and now, the shift lights don't work. Maybe a blown fuse. I will check tomorrow.

 

Just an update, the fuse was installed with only 1 prong touching. So I did the procedure to clear the TCCM and went for a drive. When I went to engage 4hi, shift lights flashed 5 times then reverted to 2hi. Checked and I have a code 2. Still wondering if I could have installed the vacuum cap in the wrong place since the pin on the Dorman switch is much shorter than original and you can only put it back on by feel. It looked like it was seated and 4 hi was working before. Kind of fed up crawling under the truck outside in the cold but, I have an encoder motor code so, I guess I will have to perform Les's suggested procedures.
Don

 

Don, have you tried the code 2 factory diagnostic chart in my old post I linked to above? Some specific things to do there.

 

Not yet Les but, it's on my list of things to do for this weekend.
Don

 

The new switch might be bad so I ordered another one and should get it Monday. Will perform diagnostic procedures once the new switch is installed.
Don

 

Well, I installed another switch. The first one I got was in fact defective. Apparently, it does make a difference because 2wd,4hi & 4lo are all working fine now. Thanks' everyone.
Don