Four wheel drive does not engage. Turn switch on.. dash lights up but wheels do not engage

SOURCE: four wheel drive wont engage

If you have push button 4-Wheel Drive, it is recommended that you use it every once in a while, in order to keep gunk, rust, and corrosion to build up on moving parts. The mostly likeley (though not definite) reason would be that you let the 4-wheel drive unused for so long that corrosion has built up on the parts and the actuator that engages the 4-Wheel Drive doesn't have the power to engage it past the corrosion. You'll need to take it in to be cleaned, or to have parts replaced. In the future, every month or so, engage 4-Wheel Drive and drive around in some mud, grass, sand, or any other loose ground for a bit, just to keep the parts moving and clean.

The service Four wheel drive light is to alert the operator the system is not being read properly by the ECU.

If the ECU loses contact with or position of the Transfer case actuator motor the service light will come on. Same thing goes for the front diff actuator.

So it may be a bad switch, sensor, or an actual problem in the 4WD linkage. This is not a Oil Change light that you can ignore a few extra weeks - it indicates a problem that should be taken care of ASAP to avoid costlier problems down the road.
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SOURCE: 4x4 wont engage

There is a switch that has twwo wires going to it, it's located just above the motor on your transfer case,on the drivers side, one plug goes to the motor and the other goes to this switch, it's the motor that shifts it into low and high range, I'm not sure what the switch is called but it tells the front end when to lock and unlock.
Hope it helps

SOURCE: My 1999 chevy silverado 1500 four wheel drive

You probably have a bad encoder motor.It is located on the side of the transfer case on the drivers side.It is black.The other problem they had with these was the switch but you have already replaced this so your next thing is the encoder motor.Hope this helps.Good luck.

SOURCE: hi i got a 96 4x4 tahoe the four wheel drive is

Are they vacum operated or you have to lock it in by hand.

SOURCE: 06 F150 4 four wheel drive wont work

usually the 4wd actuator will stick had the same problem in my 92 ranger which the f150's are the same setup you might try hitting the actuatot with a hammer it fixed mine and has worker ever since.