06 Screw, ESOF. Tried to use 4x4 high the other day and all I got was a quick flash of the light, then nothing. No sounds from tc motor, nothing. left it in 2wd instead and drove to work. Came out of work and 4X4 high light is stuck on (even when switch is in 2wd), and only rear tires powered. Didn't have time to look at it, drove it for the last few days with light on, but no 4wd. Tonight, I tried low range and sure enough, heard a clunk and low range works, but only 2wd. Goes in and out of high and low 4X4, but no power to the front wheels. Where do I start? I put in 2 new IWE's and the updated IWE solenoid last winter to fix a problem, worked great til this. Is there a write up on how to test the switch and connection at TCM?

 

Did some troubleshooting:



Drivers side - Key off, half shaft spins with wheel.

- Key on engine on, half shaft spins with wheel

- engine running 0 vacuum

Passenger side - key off, half shaft spins with wheel

- key on engine running, half shaft spins with wheel

engine running 0 vacuum

17lbs of vacuum right off throttle body

17lbs of vacuum at line going into IWE solenoid

17 lbs of vacuum going into vacuum reservoir

0 lbs coming out of IWE solenoid.



IWE solenoid pink w/blue stripe has constant 12V

IWE solenoid red has no ground in any position of 4x4 selector switch (keeping vacuum from going to front end, or opening solenoid like it should in 2wd).



Now, I assume all of the above is due to the 4x4 high light on constantly. Truck will shift into 4x4 low range (does not show on display, still says 4x4 high), then 4X4 high range, and back to 2wd, but not every time. to get the front shaft to lock, you have to go to 4x4 low first, then back to 4x4 high. It will not shift to 4x4 high from 2wd.



So, I'm guessing it's either the TCM, or switch on the dash. How do I test those 2 items?