I have a 1998 blazer, 4.3 . It has a np233 transfer case I think, 2wd high, 4wd high, 4wd low. The problem is I had it offroad in 4wd hi and now it won't go 2 hi. I hit the switch and the light blinks but it goes right back to 4wd hi. I read some old posts and tryed the easy stuff, checked the fuse, disconnected the battery to reset tccm, took it to autozone and they scanned it but didn't find anything. I don't think it is the tccm because I can hear it click when I push the button. Does anyone know if a vacuum leak at the actuator under the battery could cause it to stay in 4wd? Someone else posted a problem with theirs shifting by itself into 4wd, does the vacuum keep it from going into 4wd or is it the other way around. Thanks

 

Vacuum engages the front axles.
Transfer case shifting is electric through the TCCM and the encoder motor on the transfer case.
Were you doing any crazy 4 wheeling? Have a look at the encoder motor on the left side of the transfer case for any dirt, or anything that could be jammed up by the motor, check the wiring connector is tight.

 

I have also had problems with mine coming out of 4wd...usually on the second or third try of pushing it it will go back into 2wd. Every once in a while it will go into 4wd low when i turn it on

 

I just solved a problem on my 97 by connecting the hose to the vaccum reservoir located on the underside of the hood (driver's side). don't know if your 98 has such a vacuum reservoir, but if so, make sure it's connected.

 

thanks for all the help. i will let you know what i figure out.

 

A scanner will not display TCCM codes

Check the transfer case shift control module for DTCs. The transfer case shift control module is not a class 2 device. DTCs are displayed on the transfer case shift control switch. Use the following four steps to obtain DTCs.

Turn OFF the ignition for 10 seconds.
Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side.
Turn ON the ignition, with the engine OFF.
Observe the transfer case shift control switch select buttons for flashing codes

If the transfer case shift control switch buttons all blink only once and then stop, no fault codes are stored in the transfer case shift control module.


• When one DTC is stored in memory, that code will blink that number of times followed by a 3 second pause and then repeat.

• If more than one code is stored, the first code will blink, followed by a 3 second pause and then the second code will blink.

• This sequence will continue until PIN 13 on the DLC is no longer grounded

 

I grounded out pin 13 on the dlc and the 4wd lights flashed one time then went out. Is that the code for no problems found? Thanks

 

Code one means the power source was interrupted from the ctsy light fuse. Did you blow a courtesy light fuse at some time? If not, then you may have a poor connection at the TCCM or the encoder motor connector.

 

I rechecked the connections to the tccm and also the fuses. I got it to shift from 4hi to 4lo, but it still wouldn't go into 4hi. I crawled under and lightly tapped the transfer case with a hammer, and tried to shift it again and it went right into 2hi. I then shifted from 2hi to 4hi and back into 2hi the way it normally should, it must have been bound up or something. So it is working for now, but thanks for everyones help, there is alot of knowledge on this site.

 

Ahh yes, when all else fails use the hammer! ..lol
Glad to hear ya got it working.
Have you checked the transfer case oil level? I wonder if maybe there's a lack of lubrication....