Running a 2000 Jimmy with Auto 4wd, 2hi, 4hi, and 4lw selectors. All winter long I have used 4wd hi and low also have used 4wd hi in the past week. Today I Tried 4low and I got a click bang bump! It was a no go many of times. The truck moved as nowmal engagement but then backed out. Any ideas
Grillzy

 

Could be a number of things. Will it react the same way if you are slightly moving with the transmission in neutral when you hit the 4LO button?

 

This morning I hit the 4hi and it worked then back to 2hi, too 4auto then 4hi and back no problems. Hit the 4l no go just noise try again and it worked. hit 2hi to go back- no go - could hear the motor making a noise. tried a couple more times- stuck in 4low! Then hit the 2hi button and shifted into reverse bad grinding noise and quickly shifted back into nutral but it moved into 2hi Does this mean the little black motor on the side of the transfercase is shot?
Grillzy

 

If you haven't already done so, check the wiring connections at the TCCM, switch, and encoder motor for signs of corrosion. Clean as necessary with electrical contact cleaner and a brush.

If that does not cure your problems, the next step really should be a proper diagnosis with a Tech2 or equivalent scan tool. The NV236 transfer case cannot be properly diagnosed without it.

 

The motor at the transfer case- does it move to engage 4hi/ 4auto or just for 4 low or all? Are the 4hi and auto not vaccume. I have replaced the 4wd module (TCCM) 2 years ago acted completely different. All indicator lights etc are working as normal so are transfers from 4hi/ auto and 2hi.
Grillzy

 

The only thing that is vacuum controlled is the front axle engagement. The encoder motor on the transfer case controls all shifting of the transfer case.