My buddy's 2005 Ford F150 is not engaging 4 wheel drive. It is an Electronic Shift on the Fly system. When he turns the dial to engage the system, nothing happens. Is this a bad fuse, module, or something worse?

Operationally vacuum holds the IWE ( Integrated Wheel Ends ) out, and once vac is removed the spring engages the IWE.

Check the fuses for the 4WD system, Fuses :F111, F11, F29, F30. Use a meter to check for power on both sides of the fuse ( the small pins on the back of the fuse ) with the key in the run position.

Lift and support the front of the truck so the front wheels are off the ground ( take safety precautions, chock wheels, jack stands, etc )
Key on, engage 4x4 and try to turn the front drive shaft.
If it turns it is a problem with the transfer case.
If it doesn't it is a front axle engagement problem.

- If the front drive shaft does not turn :
Shut of the truck ( still jacked up, and supported ) remove the vac lines from the IWE. The spring should push the gears in, without the vac line on.
Check the vent line ( tube that is routed into the engine compartment with nothing attached to it ), for blockages.
If the vent line is clear, and with the vac lines off the IWE should be engaged ( both front wheels locked ).
If they lock, the problem is with the IWE solenoid not shutting off vacuum to the IWEs. There is a TSB on the 2004-2006 IWE solenoids, a newer revision has been made, and used from 2007 and newer MYs.

If the front driver shaft does turn, use a dead blow hammer on the transfer case to try to knock the transfer case shift motor free, could be hung up.

Here is a block diagram of the IWE system


The common problem is the IWE solenoid, there is a TSB that installs a water shield over it, so water cannot get sucked into the system. This is usually the IWEs making a grinding noise while in 2WD. Hope this was not happening, and the IWE gear is rounded.