I have an '03 F350 with the electronic t-case (switch on the dash) and its stuck in 4 LOW. I have tried everything, gently rocking it and coasting to a stop in neutral and nothing is working. I did some checking on wiring and there are 2 fuses relating to 4wd. They are both good. Then I went to the relays behind the left battery and there is power at the plugs for both there. Power at the switch also. Climbed under and NO power at both plugs to the t-case motor. Could this be 2 blown relays or have I got bigger problems?? Thank you in advance for any input.

 

I'm not very familiar with how these go in and out of 4LO, but I wouldn't expect there to be power at the Transfer Case until it's switching between LO and HI. It would seem stupid for it to be there to hold it in for LO. Kind of like the column shifter, you don't hold the shifter in drive once you shift it. Just a thought, that's all

 

Before you do anything else, you have to have the truck in Neutral with your foot on the brake before it will shift into and out of 4LO. Occasionally I have had to let the truck roll slightly with it in neutral and my foot just barely on the brake enough to activate the switch to get it to shift.

If neither of those work, try swapping the shift relay positions. One relay turns the motor one direction, the other relay turns it the other direction. If the "in" relay is good, and the "out" relay is bad, then switching them should let you shift out. If this works, I recommend replacing both relays. Also check the relay bases and the wiring to the relay box for corrosion.

 

P.S. In the off chance you have a manual transmission, you have to have your foot on the clutch.

 

Ohhh I should have mentioned that. It is the auto tranny and 115K miles. I did have a look at the wiring harness and it looks good, so I bought 2 new relays and I am going to replace them and see if that does it. I have done the whole foot on brake, slowly rolling and everything deal but I think its and electrical problem. So just to make sure, there are 2 boxes with relays behind the left bettery. One has 2 relays and a breaker it looks like, and the other box just has 2 relays. the one I checked was the later of the 2, this is right isnt it?

 

Yes. It's the relay box with two identical relays and nothing else. It is usually wrapped in black fabric electrical tape from the factory.

 

OK...just tried it after replacing the 2 relays with new ones. Still nothing. Power is at the plug for both relays and wiring looks good, no damage at all. There is still no power at the plugs on the t-case tho. Is there going to be any constant power there? There are 2 plugs, 1 has 2 contacts in it and the other had 6 contacts. I tried rocking the truck again and still nothing. I am kind of at a loss now. If this is the same as a manual tcase then can I maybe unbolt the motor off the side and somehow manually turn it to 2 wd?

 

The 6 pin connector is hooked to a set of switches in the shift motor that sends information back to the 4WD control module indicating the position of the motor. As near as I can tell from the diagrams there should be voltage between pins 2 and 4. But I can't say how much voltage, or if I'm even reading the diagram right. It's not very clear.

The two wire connector is the power to the transfer case motor. The relays apply power at one polarity to move the shift motor one direction, and at a different polarity to move it the other direction.

You can put a test light between the two pins of that connector and then have someone shift from 4LO to 4HI (foot on brake in neutral with key on, of course). The test light should light momentarily as the relays try to move the motor.

You can remove the motor from the transfer case and move the shaft manually if necessary.

Another test, with the shift motor removed, apply voltage to the two pin connector. Power to one pin and ground to the other. Try different polarities. Be careful with this, though. The shift motor only moves a small amount and isn't designed to have power to it for more than a moment.

Also, check fuse #111 (30 amp) in the Central Junction Box. It is the fuse for both the relay coils and the shift motor. Check it with a continuity tester and inspect the fuse base to make sure the blades are gripped securely.

 

Ohhh thats good info! Thank you, I will check that now and see what happens. If I take the motor off the side and manually shift it to 2 WD, then can I bolt the motor back on? Or is the shaft sealed in there so maybe I can just leave it off till I get it all sorted out properly?

 

I don't know a lot about the motor and shaft interface. I've never had mine off. If you turn the shaft, you'd have to get the motor to turn to the same position to put it back on, as the shaft and motor would have to be keyed together somehow.

I think that if it appears that the shaft is sealed well so that nothing can get in or out of the transfer case, it would be OK to drive without the motor in place for a limited time.