I am not sure if this provides more information or not:
OBD2 Non-Automatic Transfer Case Diagnostics

These codes would indicate that you have a problem with not only the encoder, but also the TCCM. Junkyard parts may help to rule some things out.

 

I have had the same issue for a while now. When I set the fan to be floor only it just hisses at me and does bi-level. Same thing when I try to set it to the middle vents only, except it comes out all 3 places it seems.

When i had the a/c on it wouldn't stay on the middle vents either, it would fluctuate between the middle vents then all to the defog vents and then switch back.

It did this often when on the highway, like going up a hill it would switch to defog, then after leveling out it would go back. Or if i am giving it a little gas to speed up. Thats when I noticed it the most.

 

i have a 98 blazer and i know my truck is in 2-hi. the switches are disconnected because i have to get another tccm according to my corny mechanic. is there a way to manually put it in 4-hi??

 

yes there is a pain in the ars though take the encoder motor use cresent wrench turn the stub shaft one click then take the battery out pull the cable on the vacume switch pull the cable put vicegrips on the cable so it wont slide back in put battery back in and you got 4x4 lots of work i would not bother with it

 

So I decided to take my car into the dealer for a full diagnostics before I bought anymore parts. They told me my 4x4 was fixed by just clearing the codes. There were error codes resulting from a bad on dash switch, which I had already replaced. My 4x4 seemed to work when shifting it in the parking lot, however I did not have a chance to see if it was actually engaging. This morning when I left for work none of the lights on the switch were on, including the 2hi light. After about 20 minutes of driving the 2hi light randomly came on. I am now back to where I was. I am bringing it back into the dealer tomorrow and I will update then. Do you still think there is a problem with the encoder and TCCM even thought it was temporarily working? The dealer did not mention anything about these!?!

 

Had the same problem. Went to the junk yard to get a transfer case and explained my problem to the guy and he told me to spray the electrical connector going into the T-case with WD-40 or some lubricant and clean it out good.
At that point I already had it out so I did what he said and connected the connector back to the t-case and still had it out of the vehicle. I then tested it with the vehicle not running and it went right in 4 hi and out of 4 hi with one push then went in 4-lo with one push when in neutral. (94 S-10 Blazer) Havent had a problem with it and it has been year and a half. Guy saved me several hundered dollars.

 

Just to update, the dealer re-ran the diagnostics and said there was a problem with the encoder. Once again, after getting it back from the dealer it worked fine until a few days ago. I looked at the plug connection like buggyblazer said, however it was clean. I hope to change the encoder motor within a few days and will update again.

 

vacuum switch stays on all the time. could it be vacuum switch no good, how do I test it....

 

So I finally changed the encoder motor today. I bought a used one from a junk yard for $50. After swapping them out I tested the new one, but continue to have the same exact problem. Either this salvaged encoder is also bad, or this is another problem. I am now going to look more into a TCCM problem, if I get enough motivation to keep trying to fix it...

Anyways, this is a useful link that describes with pictures how to remove the front drive shaft and how to remove the encoder motor. The biggest problem for me was keeping the drive shaft from turning when unbolting the U joint.

http://www.zr2usa.com/mboard/index.p...=encoder+motor

 

I tried to run my own diagnostics again by grounding pin 13 however none of the 4x4 lights lit up, not even when I first turn the ignition, before the error codes should be displayed. When I am not grounding pin 13 and turn the ignition all 4x4 lights are lit and then go out as normal. Any ideas? The link does not mention anything about them not lighting up.