so Im a little puzzled with my 4x4 at the moment, at 1st my 4wd hi and low worked fine then all the sudden 4hi quit, but 4lo continued to work. Expecting large amounts of snow I decided I better get my 4hi working, well I’ve tried everything I know to do and still no success. WHAT I HAVE TRIED~ replaced actuator under batter, replaced the cable that attaches to the actuator and differential, replaced the vacuum switch on top of transfer case, I put a TCCM from another s10 with working 4x4 in it and still nothing. I haven’t tried swapping push buttons, but I think they’re working because when I click the buttons I hear the encoder motor shift into 4wd and then back out quickly. (To simply explain). It seems to be that the TCCM is telling the transfer case to shift into 4wd, then the vacuum switch engages the actuator(I watched it move) but for some reason somthing tells the transfer case to shift back to 2hi. My big question is, could the indicator sensor on the front differential( right where the 4x4 cable attaches) be bad? If that sensor is bad possibly the TCCM thinks the diff is not engaging and returns the TCase to 2hi? I’m not sure what else could be wrong since I have good vacuum, must be electrical?
Any help is greatly appreciated!
2000 blazer
3 button 4x4

 

Does that other S10 have the same transfer case? If so , yank the encoder motor out and try it in your Blazer..

Heard somewhere before (Blazer Forums, uhem..) that if it only goes into 2 Hi and 4 Lo , then the Encoder motor is probably failing as it will only go from one extreme to the next..

Just a thought based on what I have seen and read..

 

Mine was doing the EXACT same thing. I replaced the switch and cleaned the connections. Hold it in 4 HI and if you're lucky, it'll stay.

 

 

I have not read anything about there being a sensor on the front diff, nor do I remember seeing anything when I have worked on it.
The only sensor I know of is within the encoder motor.
I have had success with removing the 4x4 switch from dash, CAREFULLY separating the two halves of it and re-soldering all of the connections.
As suggested above, could be the encoder motor as it could not be telling the TCCM that it is in the 4HI position so the TCCM commands it back to 2HI after a time-out.
Again suggest working on the switch as it is an easy, quick, no cost attempt.

Snow?...what is that?....going to be 75 here today.