I'm helping my uncle with his 2000 gmc sierra 1500. The service 4wd light has been on since he got it. First thing he did was replace the dashboard switch. This didn't fix the problem. Then I helped him replace the transfer case motor. He said this solved the problem temporarily. I believe he was only driving in 2 hi. The problem came back within a few days from what I heard. He just ignored it and continued to drive in 2 hi. The other day he was stuck in the mud and tried to switch to 4 hi, it switched but then he was stuck in 4 hi. Theres also been a grinding noise when he goes in and out of park, not sure if that's related. What kind of things could I look at to fix this?

 

test the motor
if it failed again then it was a bad motor, or it's time to rebuild the transfer case

 

Ill definitely do some more testing, I’ll put a power probe to it and see what happens. he just bought another new motor and you can hear it trying to do something, I know it’s getting power. And the transfer case can be moved manually and drives fine that way, with the motor off. Very confusing that both seem to be working separately but not together. Unfortunately the motor can’t be tested unless it’s attached to the transfer case.