I have an O2 F350 with ESOF. I is not working at all. When I turn the key to run to start the truck neither of 4x4 dash lights come on during the lamp test. Nothing happens when I turn ESOF switch to 4Hi or 4Lo. Have tried manually locking the hubs, nothing happens. Don't have any symptoms of a vacuum leak. Have crawled under the truck by the transfer case, had my wife play with ESOF switch, but no sound from the shift motor. Have not had a chance to remove the shift motor to check it if still works. Have checked all the fuses that I thought could be related to the 4x4 system.

What relays are part of this system and where are they located?

Is it a problem with the GEM module?

Thanks for whatever help anybody can offer.

 

Welcome to FTE, jheintze

Since the indicator lights on the dash are not coming on it sounds like you have a blown fuse. Have you checked all fuses including those under the hood?

Check your owners manual carefully and you can locate all the fuses.

Let us know after you've checked them.

BTW, locking the hubs will not engage the 4wd system. All that does is engage the hubs to the axles. You need to engage the transfer case. Seems like the servo motor isn't getting the signal. That's why you need to check all fuses.

 

Thanks for the response Big Orn. I do understand that locking the hubs doesn't engage 4x4 system. I was just covering all the bases on what parts work and what parts don't. From reading all the posts on this site I've got a decent understanding of how the system is supposed work.

Anyway, I will probably go through the whole fuse panel under the dash tonight to make sure I don't have any blown fuses. BTW where is the fuse panel under the hood. I have seen a couple of black boxes with relays near the master cylinder, but no fuses panels like my 95 F250 had for main power and trailer lights? Are any of these relays for the 4x4 system?

Thanks for the help I will get back to you with what I find.

 

The fuse box under the hood should be next to the fender, driver's side towards the cab. Can't miss it.

 

Okay, I visually checked every single fuse in the fuse panel under the dash, I swapped the 6 or 7 seven relays around that are on the fuse panel to make sure that it wasn't a bad relay. There 3 small black boxes with relays in the engine compartment behind the air filter box. I determined that the one cluster of 3 relays is for the daytime headlights, so I used that cluster to check all of the relays in the engine compartment, all of them work. The last thing I did was disconnect the batteries (Diesel) for half an hour to reset the computers. After all that I still do not get 4x4 lights in the instrument cluster when I turn the key to the run position. Everything else on the instrument cluster that is supposed light up did light up.

What next?

 

Sounds like you've covered the bases. The only thing left is to check continuity in the wiring - make sure there are no damaged wires, etc.

With that said, though, it could be the GEM. If you can't find damaged wiring it looks like it's time to see the dealer or your mechanic whichever you trust the most.

 

Which wiring do I need to check for continuity? To the ESOF switch, both connections to the TC Shift Motor? What else?

Thanks for your help

 

Since the lights on the dash aren't working I'd start there. You need a wiring diagram that I can't help you with.

Maybe some will come along that has one.

Do you have a voltmeter? You can check the wires to the servo motor on the transfer case.

ON EDIT: You might want to check the fuses to the GEM also, even if you have to unplug the GEM and plug it back in. Sometimes you can reset the system by removing the battery cables for a few minutes.

 

Okay, I got a wiring diagram and a test light. I checked each fuse on the wiring diagram for power to the fuse and continuity through the fuse. They all checked out ok. I checked for power at the relays under the hood, with the diagram I was able to determine which relays are for the 4x4 system. Through playing with the relays I was able to determine that the transfer case shift motor works (at least in one direction).

I also pulled the ESOF switch out of the dash and this is where I'm seeing a potential problem. There four wires in the connector to the switch, two are for the illumination led and the other two are for operation of the switch. There is power to the led and it illuminates. There is no power to the switch it self. It seems to me that there should be power to the switch when the ignition is in the run position. I even tried starting the truck and checking for power at the switch with the truck running. It still didn't work.

Also I did the instrument cluster self-diagnostic test. During the bulb test the 4x4 and 4x4Lo lights did work. I realize the only thing this shows is that there isn't a problem in the instrument cluster.

The next thing I plan to check is where the wires are connected to what my wiring diagram calls the "Four Wheel Drive Control Module". On my 02 F350 it is located behind the glove box. I wonder if this control module is the same as the GEM module?

 

Sounds like your switch isn’t getting the signals. Hard to tell…
Here’s the location of the GEM (Generic Electronic Module):
http://dieselinnovations.com/techfil...4_location.pdf

Have you checked the servomotor to make sure it’s functioning? If you remove the motor you can apply 12v to it to the pins to check the movement of the motor. With the motor off transfer case, you can crank the t-case with a socket wrench to selection of the 4x4 (2wd-4HI-4LO) and this should light the dash light (with ignition key turned part on). Be sure to mark the position of the crank nub and the motor spindle before you turn it so you can put the motor back on afterwards.

 

Well, I don't know what I did, but it works now. I drove it this morning to the bus stop and for some reason I decided to try the switch. What do ya know, it worked so when I got to the parking lot I tried the 4Lo and it worked too. I tried it again tonight in a church parking and everything worked including the hubs. So hopefully it lasts. Thanks for all your help

 

Sometimes it's as simple as un-plugging a fuse or the GEM and plugging it back in.

Glad you got it working.

 

By any chance did you unplug the connections at the shift motor on the transfercase.?
Corrosion usually hits there first.You may want to put some dilectric grease in those connectors down there because thay are exposed to the elements more often.
Rich

 

I never touched any of the connections on the shift motor. I really think that one of the contacts on one of the relays was dirty. However, that does not explain why I did not see any power at the selector switch on the dash. Anyway I hope it continues to work.
John