1999 Ford F250 No 4 wheel Drive

30

Asked by Oct 31, 2014 at 12:57 PM about the 1999 Ford F-250 Super Duty Lariat 4WD Extended Cab LB

Question type: Maintenance & Repair

I have power to switch, replaced switch, turn to 4 hi, no light, removed transfer case motor, verified that it was still in 2 hi, installed new motor (motor was in 4 hi) manually shifted transfer case to 4 hi, 4 hi light came on on dash, would not shift out of 4 hi, replaced both relays, still would not shift.  I believe there is no power going to shift motor.  What else can I do?

11 Answers

78,535

You need to listen for the relays switching when you change modes on the 4X4 switches, they are hard to hear so everything needs to be shut off and quiet as possible, make sure doors closed, engine not running, key on, then try switching modes and listen for the relays cycling, if you don't here the relays then you need to do a circuit trace on the 4X4 electronic shift controls and module assembly, you will need a shop manual with a wiring schematic for this system to do that.

1 out of 1 people think this is helpful.
30

Thanks for your response. Turned on ignition to run, turned switch, no sound from relays. Got helper, turned on ignition, put my fingers on top of relays by fire wall, had him turn the switch, nothing. Replaced both relays, no difference. Removed relays and checked for power where they plug in. 12V under both relays.

78,535

Ok so you have relay power but the control unit is not sending the signals to relays for the modes, could be the control box, could be a wiring problem. Do you have the schematic for the system? If not I suggest you get one, you are going to need it if you are going to track this down yourself. Or you could try your local library's reference section for the shop manual.

30

I have a wiring diagram. All roads lead to GEM. Any other options?

2 out of 2 people think this is helpful.
78,535

If your switch commands are there to the GEM, and the GEM is powered up and grounded properly but nothing is coming out for the transfer case motor then it is most likely the GEM. They do fail.

30

Thanks again. To summarize, when you put the 4x4 switch in 4Hi, it goes through the GEM, activates the relays to energize the TC motor to move TC lever. When you move the switch back to 2Hi, the relays are activated to reverse the motor to move the TC lever back to neutral. Position switches on the motor assembly stop the drive motor. Am I missing anything?

78,535

You got it all right except the position points on the transfer case motor, they tell the GEM what position the motor is in so it can shut it off at the desired mode.

30

I ordered the GEM. Should be in next weeks sometime. I'll le you know how things go.

30

OK, installed new GEM. I've got more bells and dingers I didn't know I had. Turned on the ignition, turned switch to 4wd, it went to 4wd and 4wd light came on and I was feeling pretty happy. Until I tried to switch it back to 2wd. No luck. Now it's stuck in 2wd. Unplugged power wire to TC motor, checked wires. Both go to ground. Turned on ignition, turned 4wd switch, no power. Power to switch, all fuses good. Took to shop. They spent 3 days on it and gave up.

30

If anyone is interested, it's fixed. Took it to the Ford dealer and they tore into it. They came to the conclusion that a wire was bad. They unplugged the looms and stripped off the coverings. They found 4 broken wires and fixed them and put everything back together. About a 7 hour job. No explanation as to why the wires broke.

1 out of 1 people think this is helpful.
78,535

I thought you checked your wiring, it was most likely the loom that goes to the transfer case motor, but it should not have taken that long to find it especially at a dealer with access to all of the Fords TSB on this system. I would look underneath and make sure they recovered the loom properly, you don't want water getting in there causing more problems. Thanks for letting us know, every bit of information has value, maybe someone is having the same problem.

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