I have a 03' silverado and I have issues with my 4wd. Periodically it will start up in 4lo and I go to hit 2hi and it just flashes then service 4wd flashes on dash. I have to turn truck off to get it to normal most of the time. Does this mean a bad switch in dash or something in front end? Please help!!!
Also, how do you test if your switch is bad??

Thanks