Ok so several weeks ago I replaced the shift motor for the second time. Mechanic said it was defective and I figured the same. So just to recap.

Rebuilt front drive shaft
new vac hoses
new cable
new actuator
new switch

Since then I have only used 4Lo once and 4i twice. for the past week everyday I have played with the buttons in the driveway (not moving) switching between 4Lo, 4Hi, 2Hi, Auto. Yesterday I decided to try it in the backyard in the field. Out to the field 4Hi works back into 2Hi works flip back to 4Hi no problem. I put into 4Lo now won't come out. I put into drive move a few feet straighten tires try again, still won't come out. Drive back to my driveway stop again push 2Hi it switches. Back out to field try again once in 4Lo it won't come out. Back in driveway switches no problem.

Why? What is it sensing??? Why won't it come out of 4Lo when in a field (I have tried this on perfect flat and on slight incline and slight hill.

 

Something new. Now it will not go into 4Lo at all. It makes the clunk sound then comes back out. Another thing I noticed is the cruise control does not work, could this be related? I have no 4x4 codes, but could this all be cause by the transfer case output shaft sensor?

Hope someone else has some knowledge of this. After trying 2 new shift motors and replacing most everything it still not working. Myself trouble shooting it and 2 30 year mechanics.

Anyone have any ideas This is the NP8 transfer case 2001 4 dr Jimmy.

 

New dash switch or vac switch?
You could take a look at 4x4 module over behind the kick panel on the pass side and spray some QD electronics cleaner on the connections. I have heard of that helping.

 

Vac switch is new. Dash switch is original. TCCM is new. I'm thinking speed sensor. because of the symptons I described after replacing the first Shift Motor it worked for about a week then went again with same codes so my mechanic figure it must defective. This time it is doing almost the same as I described above, except I may have blown the other one because I sat there for a very extended period of time pressing the 4 LO possibly damaging the shift motor. For a while it would shift into 4Lo when on the lawn but only shift out when on something good and solid like the road. Were the sensors sensing something because they are defective and telling the computer it cannot shift into 4Lo. I can still get into 4Hi. 4 Lo requires the truck to be in Neutral and moving less then 3 km/hr

 

Why don't you look at what some other speed sensor symptoms are, I don't know but would think the tranny would be shifting funny through its normal range.

I can tell you I have gone through three dash switches. The aftermarkets are real crap and I don't know if springing for GM is any better. When they go you get all kinds of wacky symptoms.

 

I just tested the resistance of the rear prop sensor and it's perfectly in the range. My mechanic as you also suggests the dash switch. But what doesn't make sense is it will go into 4Hi and Auto, it will attempt 4Lo but then go back into where it was previously. I think I have a buddy who told me he has a brand new switch I will try that.

I wonder are there tests that my mechanics and I are missing that GM would do?