I have this issue with my 4wd I can't figure it out it's the 4 butten switch. Whenever it rains out for a while with the truck sitting it will automatically go into 4wd even though the selector switch still says 2wd I have checked the tccm everything looks good no corrosion nothings wet vacume hoses look good I don't know what else it could be once it stops raining maybe 8hours after everything is back to normal no issues everything works fine any help figuring this issue out would be appreciated thanks

 

Just to be clear, is it that your truck is actually going into 4wd with the transfer case and front axle engaged or is it only that the indicator light on the 4wd selector switch is illuminating the 4-hi light?

 

its actually going into 4wd but the indicator light still says 2wd or will be not lit at all its been dry here for a few days everything is perfect it goes into 4wd perfectly and 2wd perfectly just when it rains alot it acts up im wondering if the vacume switch on the firewall is shorting out or something and causeing the issue