Hi all i have abit of as strange fault on my 2003 f150 5.4 4x4. I've had the truck about 2 years and the entire time the 4x4 has acted weird. Shortly after getting the truck the 4x4 stopped working completely the dash light wouldn't come on and i couldn't hear any relays click. Then a few months ago it seemed to start working as the lights would come on and i could here it engage and the relays click but the the back wheels would still just spin when trying to use it. Fast Forward to yesterday into this morning we got over a foot of snow and i tried the 4x4 again and it worked great driving through 6+ inches of slush/snow from a dead stop no problem i could also feel the front wheels binding when turning so i know it was engaging. Now tonight i try to pull up my snowy driveway and the back wheels just spin again with the front doing nothing. Anyone have any suggestions on what could be causing this intermittent fault? Thanks in advance for any help.

 

The usual culprits are bad shift motor.....if there's no lights or clicky clicky, or it works intermittently.

or
Bad front shift fork or vacuum tubing..... If it seems to shift and you have lights but there's no front wheel drive.

Other issues are less common. But can include relays, gem, solenoids, grounds, bad wire someplace.

If there's a problem with the four wheel drive shift motor... The system is disabled after a self test that occurs when the vehicle is started and it doesn't do anything. Of course if other parts of the system fail the same thing happens. There are actually codes that will store in the PCM . I think you may be able to read these with forscan. These may act erratic before they quit working altogether. I found out mine no longer worked when I was stuck on the side of a road that I pulled off of to park at a kids sporting event.