Alright, here is my story....I have a 1998 Blazer. I was having trouble with my 4WD last year. I was told to check the actuator under my battery tray. I found out that it was busted and that fixed my problem. About six months ago, I would be driving down the highway or whatever and I would hear a loud roaring noise. I was told to check the vacuum switch on my transfer case. I replaced that and it took care of that problem. Now, when I try to put my vehicle into 4HI or 4LO, I hear the noise that sounds like it is kicking in, but it doesn't because neither front tire will spin. So the front driveshaft is not turning for whatever reason. I have looked at all my vacuum lines and they seem to be in great shape. I found out that somehow my oil filter had came loose and was leaking oil, which I have fixed now. The plug that I found on my front axle that I believe is called a indicator switch had oil in it. I cleaned that plug out and plugged it back in and it still didn't work. Another thing that my uncle did for me so that I wouldn't get stranded anywhere is he took the cable out of the actuator under the battery tray and zip tied it to a place in my engine. He showed me that if i pull out the end of that cable a little ways and put the truck into 4LO inside on the dash, then I will have 4LO only. No way to get 4HI until I figure this problem out. If you have any ideas, PLEASE let me know.

I forgot to mention that the 3 button switch on the inside of my truck works fine. If there wasn't snow outside and I didn't get stuck, then I probably wouldn't have noticed it wasn't working. Everything sounds like it kicks in and the 4LO would kind of feel like it was pulling me back like I was actually in 4LO but neither front tire or the driveshaft was spinning.

HELP!

 

Do the lights on the switch light up solid indicating that the TCCM thinks the transfer case has shifted into 4HI or 4LO after pushing the respective buttons? If it does and the front driveshaft still does not spin, there is either a problem inside the encoder motor that has caused the motor to not turn the transfer case sector shaft or the transfer case itself has an internal problem.

Have you tried to pull the codes from the TCCM? OBD2 NV233 Diagnostics
Note: If you have recently disconnected the battery and/or TCCM, there will be no stored codes.

 

Yes, the lights on the inside switch light up solid as if everything is normal.

I did the data link connector test on the 13th pin and it showed no codes.

Is there any way that an encoder motor can be tested before having to buy a new one?

 

The problem with much of the testing is that you either have to back probe the pins and see if the channels are doing what they are supposed to do or you have to use a pretty sophisticated scan tool to monitor the channels during a shift request. But yes, the encoder motor can be tested.