20-30 car accident on the highway, took the side roads and freaked out when the 4WD didn't engage. 2000 F150 5.4 with shift on the fly. Never had any problems like this before. Tried brakes on, off, neutral, restarting, and turning the switch back and forth. I also quickly checked fuses 3 and 23. Last week I did pull the alternator to get checked, had some electrical issues, not sure if something blew or shorted out? Also while I was underneath I did notice a leak from a pressure line on the drivers side, almost behind the headlights. What is this? The fluid was red and the unit it was going into is really rusted on the bottom. I saw a link that people were directed to with this issue, but that person had a dash light and clunking, which I don't have either. Haven't had any other tranny issues. Where should I start until I can get a manual?

 

Check maxi fuse #104 for transfer case motor.
If ok then you need some help looking at the operation of the case motor.
If it operates then look at the firewall solenoid, vacuum lines to the front actuator and actuator for operation.
If nothing works it's back to the GEM module where you give it the signal from the dash switch.
Until you get a lead on it it's just guessing.
Good luck.

 

#104 was ok, any other ones besides 3 and 23? Too cold to get at it yet. I do hear like 4 clicking sounds from the switch, the first time I turn it on. Does that help? Otherwise, I'll post after checking a few things

 

If you dont use your 4x4 for 8 months or so they can stick rap the motor with a hammer. It helped several times in our shop already this winter.

 

When I finished building my truck my 4x4 didn't work the first time I tried using it. After crawling under the truck I found that the vacuum line had popped off of the solenoid as Bluegrass mentioned above. However, I think my light on the dash still lit but it just wouldn't engage the front dif because of the vacuum line.

 

Rapping on the motor didn't help. Are there any fuses besides 3 and 23 and the big 104? I was hoping for an easy fix. So I have to start digging deeper. I see the solenoids on the firewall where the pink and blue vacuum lines come out. How do I check the voltage to them, when someone turns the switch? If I disconnect the connection, the holes in the connecters are too small to put my meter probes in.