2001 S-10 Pickup switches into 4WD on its own

[oldebondo]

4.3L automatic LS, 42,000 miles: Just driving down the road, the 4WD Lo button starts blinking waiting for right conditions to switch into 4WD. If I hit the 2WD Hi button twice, it cancels until the next time. Seems to do this twice a mile or so. Is it the button giving a spurious signal or did a mouse chew through some wires? I appreciate any ideas on where to look. Thanks in advance for your kind and informative replies.

[MT-2500]

If a 233 transfer case check for codes.
Ground pin 13 diagnostic connector and count light blinks and post back.
MT

[oldebondo]

Originally Posted by MT-2500

If a 233 transfer case check for codes.
Ground pin 13 diagnostic connector and count light blinks and post back.
MT

I checked both with a code reader and as prescribed by you: No codes were set according to the code reader; when pin 13 is grounded, there were no lights on at the 4WD selector switches; no blinking no nothing. What does this mean?

I ordered a cheapy switch off Ebay just to try. My gut feel is that it is the switch but you never know what you don't know until you find out that what you do know is not enough.

Thanks in advance for your informative reply!

[MT-2500]

Does the lights come on for a bulb check with key on?
Check all fuses and plugins and wiring.
Also check plugins and wiring on transfer case module.
Let us know what the switch does.
Good luck.
MT

[oldebondo]

Originally Posted by MT-2500

Does the lights come on for a bulb check with key on?
Check all fuses and plugins and wiring.
Also check plugins and wiring on transfer case module.
Let us know what the switch does.
Good luck.
MT

Yes, without pin 13 grounded, the lights do come ON for a bulb check when the key is turned ON.

Will the TCCM default to 2WD if the switch module is unplugged? (Assuming the TCCM was last in 2WD.)

[MT-2500]

If you get it into 2W and unplug everything it should stay there.
MT

[oldebondo]

Originally Posted by MT-2500

Does the lights come on for a bulb check with key on?
Check all fuses and plugins and wiring.
Also check plugins and wiring on transfer case module.
Let us know what the switch does.
Good luck.
MT

Yes, without pin 13 grounded, the lights do come ON for a bulb check when the key is turned ON.

Will the TCCM default to 2WD if the switch module is unplugged? (Assuming the TCCM was last in 2WD.)

[MT-2500]

Not sure about the defalt But.
If you get it into 2W and unplug it it should stays there,

[oldebondo]

I just wanted to get back and post what my final solution was:

I purchased a replacement switch assy on eBay and the problem went away. I disassembled the original switch and cleaned some "black stuff" from the space between the contacts using IPA and a Q-Tip.

[MT-2500]

Thanks for posting back how it went and the fix.
Glad you found the problem and got it fixed.
Good luck
MT