Switches from 4 auto to 4 high on key cycle

[bodabdan]

I replaced the transfer case servomotor about two years ago. It's been working great and although I rarely need 4x4, I do cycle the transfer case through 4h/4l/auto settings monthly or so.
With this recent snow I drove it in 4 auto to the tire shop for new rubber. When I got back in it, it was in 4h. I thought the tire shop guys might have done it but they didn't.
Turns out that if I shut it off in 4 auto, it's in 4h when I crank it back up. Does it every time. In every other aspect the drivetrain works fine.
Any thoughts on what might cause that? TIA

 

[Fless]

Is it actually in 4hi, or is the switch just indicating that? Could be the switch or the encoder motor. Or in rare cases the TCCM or transfer case, but those are remote.

When you start it up in 4hi, can you switch it to another mode, and can you hear it switch?

 

[Doubeleive]

the 4 wheel drive switches are historically known to either change modes with a key cycle or sometimes get stuck and only switch modes if the button is held in for the desired mode while starting.
if everything else checks out and nothing else makes sense then it could be the switch but there not cheap so best to rule anything else out first before trying a switch, unless you can return it. I think dorman is the only one that sells new ones last time I checked

 

[Fless]

You didn't list your year. The earlier GMT800 switch part numbers are different from mine, but I don't know if the button resistance values are different.

You could disassemble yours and clean the contacts. I've pulled several OE ones from UPull yards and refubished them by cleaning and fixing the backlighting.

See this post:

“Service 4WD” message

Switch measurement procedure here, starting at about 2:10 into it. Auto4WD = 61.7-68.1 ohms 4HI = 656-760 ohms 2HI = 1.50-1.53 K ohms 4LO = 2.32-2.37 K ohms Neutral = 1.015-1.035 K ohms Pics of switch internals. On the last pic, reflow the solder on the pins in the rectangles, and clean the...

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