Ok, so I have a 94 s10 with the 4.3 and the 233 transfercase. The 4wd worked fine until one day driving in the snow I was in 4hi, pushed the button to go back to 2hi and the lights flashed and then both lights stayed on. It drove like it was in 4lo but worse. Finally after pushing the buttons over and over it came out. I hadnt tried to use it again until the other day (a year later). It went into 4hi fine. Parked the car and had left it in 4hi. Next time I get in it the light was off (green 4hi), I tried pushing it to turn it on and nothing. After driving it I can tell it is still engaged but the light doesnt show it. Ive tried disconnecting the battery and pulling the TCCM fuse with no results. I did the jump on terminals A and J and all I got was a code 1. I dont get it. Help me please!

 

https://blazerforum.com/forum/tech-a...ill-help-7180/ Check this thread.

 

Thanks for the link, that was some good info. So I went out and did an inspection on the vacuum actuator and as soon as I start the truck vacuum was applied to it. I suspect the valve on the transfer case but for now I just plugged off the line at the actuator. I then noticed while driving the 4Hi green light came on. I pushed it to turn it off and this time heard the TCCM click. Hadnt come back on since. Do you think the switch has gone bad or a relay in the TCCM is sticking. When I start the truck both the 4Hi and 4Lo lights come on for a sec like they should and then go out. Switch on the dash maybe?

 

Sounds like the Vac switch is bad to me.