Hi all, long time lurker. I’m usually able to search for an issue and find the solution here, but this one has me stumped. I’ve found a lot of useful information and hopefully eliminated some potential causes.
Earlier this week. I backed my truck out of my garage, put the truck in park for about 60 seconds, and when I came back the truck was in 4 low. The 4wd dash switch doesn’t seem to do anything, and the truck would switch between 2h, 4h, and 4L on its own. The dash lights would indicate whether the truck was in 4wd. I tested the switch with an ohm meter, and it came back with the expected resistances in all 3 positions. I felt vacuum at the actuator, but since I’m not able to take the truck out of 4wd, I was not able to test both lines.
It seemed like the most likely culprit was the transfer case motor, so I replaced it. The transfer case was in 4 low, so I manually moved it into 2high so I could install the actuator. It was somewhat difficult to move it to 4 low, and it made a ping noise when I got it from 4 low to 4 high. It was easy to get from 4 high to 2 high.
I started the truck and tried the switch. I did hear relays clicking which is more than it was doing before. When I tried to put the truck in gear I could hear some banging noises, so I put it back in park and decided to ask for help.
Is it because the truck was in park when I moved the transfer case? Should I put it back in 4 low and try again? Any other ideas? Thanks!!

 

Have you seen this?

https://www.f150online.com/forums/vi...diagnosis.html

 

I just watched it. I hadn’t seen it before. This reinforces my belief that the vacuum system is not the culprit. Thanks for posting that.