Ok, In another thread I posted that my sons ZR2 was having problems with his 4x4, the Encoder Motor was making a weird noise, or no noise, I tried another Encoder Motor And had the same issue, after some searching on the internet I found that the transfer case control module sometimes gets corroded, this was the case with my sons, not only was it corroded one of the pins had corroded to the point where it had broken off, I took a look at the prices of the box $200+ for a new one , I took apart the module, soldered a wire to the leg with the broken pin, ran the soldered wire out of the control module box and soldered it to the corresponding wire in the vehicle harness, 4x4 works great.

Hope that this helps someone else out..

 

Good to know...i was lucky...mine only needed a good cleaning.
Harness looks like future suspect though...this will be something for me to try when the time comes.

 

1999 blazer Lt 4x4 with automatic trans and auto 4x4 ..... upon start up wants it automatically goes into 4x4 auto and will not shift out of. cleaned up eccm connectors like was recommended in here but issue stil remains service 4x4 light is on and only way to get it into 2 whell drive is disconnect front dif wires for 4x4 ..... need help is there something i am missing a step i have over looked