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Steve Jensen
Steve Jensen, Ford Technician
Category: Ford
Satisfied Customers: 394
Experience:  Ford Senior Master Technician, ASE Master Technician 33 years experience
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2000 f250 super duty: selector switch..electric shift motor..engage

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2000 f250 super duty diesel automatic, and four wheel drive. How do I know if the transfer case selector switch is bad or if it is the electric shift motor on the transfer case.
Nothing happens when I try to engage four wheel drive. I checked all the fuses and they are good.

Roger, 1st, check fuse #17 in the engine compartment fuse box (30 amp) and fuse #19 in the underdash fuse box (I see you checked the fuses, but just want to be sure). Beyond the fuses, the best way to diagnose it is to use a scan tool that is capable of reading the data from the GEM module. This module controls the transfer case shifting along with several other things. With a proper scan tool, you can read the switch positions and the shift encoder on the shift motor. This is a difficult system to test without the use of a proper scan tool. Feel free to question me further if you need to. Steve
Customer: replied 8 years ago.

Are you telling me I cannot check the dash switch without the use of a scanner.

I have no power to the switch. I have pulled it out of the dash and have checked it for power and there is no power to it. I guess I could check the switch with a ohm meter, but I still need to know why there is no power to the switch.

Any more thoughts?



The four wheel drive mode switch provides a change in resistance across terminal #'s 3 & 4 at the Gem module, the only voltage you will read across the switch will be reference voltage from the gem module, which must be read with a digital voltmeter (5 volts). The gem module is capable of shutting this voltage off if it sees a problem in the system. If you check across the two center terminals of the mode selector switch connector, 2wd should read 3700 to 4100 ohms. 4wd high should read 1050 to 1150 ohms. 4wd low should read 340 to 380 ohms. The problem with trying to diag this system without a scan tool is that the GEM module will not activate the 4x4 shift solenoids to rotate the shift motor without seeing the correct inputs, including the shift encoder (located on the shift motor). The encoder has to show several contact positions at once to tell the GEM module what position the motor is in. If the reading is incoherent then the module will just refuse to activate the system. The most common cause of the symptom you have is a failure in the shift motor encoder... Hope this is of help to you ...Steve
Customer: replied 8 years ago.

You have been very helpfull. One last thing I need to undestand, is the shift motor encoder located in the transfer case shift motor?



Yes, the encoder is part of the shift motor. I contains 4 pairs of contacts that show on or off sequences based on the position of the motor. Good luck. Steve
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