I haven't posted this or seen it posted in awhile.

This is the right time of year and the right thread.

Principles of Operation — Electronic Shift on the Fly (ESOF)
Transfer Case

The four-wheel drive electronic shift on the fly feature electrically shifts the vehicle transfer case between 2WD, 4X4 HIGH, and 4X4 LOW. The system mode is selected by the operator through a three-position rotary switch on the instrument panel. The operator is informed which mode the system is in by two cluster indicator lamps, one for 4WD HIGH, and one for 4WD LOW (in 4WD LOW, both the lamps are on). Shifts into 4X4 HIGH can be made at any speed.


When shifting into or out of LOW range, the generic electronic module (GEM) requires that the vehicle speed be less than 5 km/h (3 mph), the brake applied, and the transmission in NEUTRAL (A/T) or the clutch pedal be depressed (M/T). (The digital transmission range (TR) sensor informs the GEM when the transmission is in the NEUTRAL range position.)

The electronic shift motor is mounted externally on the transfer case. It drives a rotary cam which moves the mode fork and the range fork within the transfer case between the 4X4 HIGH, 4X4 LOW, and 2WD range positions.

The 4X4 shift motor uses two relays which, under control of the GEM, shift the transfer case shift motor between 4X4 HIGH, 4X4 LOW, and 2WD modes.

The GEM accomplishes shifts system modes by interpreting inputs from:




<DIR><DIR>4X4 selector switch.
Vehicle speed signal (transmitted from the ABS system).
Transfer case.
Brake switch.
Digital transmission range (TR) sensor (automatic transmission).
Clutch pedal position switch (manual transmission).
Ignition switch.




</DIR></DIR>Based on these inputs, the GEM controls the shifts into 2WD, 4X4 HIGH, or 4X4 LOW with the following outputs:




<DIR><DIR>Low to high relay.
High to low relay.
Vacuum hub lock solenoid.
Transfer case shift motor.




</DIR></DIR>The ESOF system has a feature which allows the driver to override the vacuum operated hubs. When the front hubs are manually turned to the LOCK position, the hubs are locked at all times, overriding the vacuum operated system. If the front hubs are manually turned to the AUTO FREE position, the hubs can only be locked by turning the 4WD mode switch to one of the 4WD positions.If the front hubs are unable to be unlocked by use of the 4WD mode switch, the hubs may be unlocked by turning the manual locking hub from the AUTO FREE position to the LOCK position and back to AUTO FREE.

NOTE: GEM as referenced here is for years 1999-2001. 2002 and 2003 have a separate 4WD Module.

Here it is in PDF:

Thanks PaysonPSD. That is some good information. Below is my conclusion.

I'm afraid I'm going to have to take this problem to the dealer. The solenoid will not function no matter how I try to use the selector on the dash. Fuses are all good. I tested the wiring harness at the shift motor on the t-case and got nothing. Of course I had to have one of my kids help me so I only attempted it with the truck off. I could just see it now, "Hey what does this lever do?" I tested the shift motor by grounding my voltmeter and inserting the hot lead into one of the sockets on the harness.

I also pulled the box where the relays are and looked at the back of them for corrosion. There's some oxidation but they look like they are in good shape.

I also tried putting my voltmeter on the sockets where the relays are. Used the ground where pin 85 should go and then tired all positions while having the 4WD switch moved back and forth. I don't know for use if that was a good diagnostic effort but regardless I got no change in reading when the switch was moved.

I'm inclined to believe it's the GEM. Just my luck the most expensive part and I have to have the dealer (or other repair facility) install and program it. :-banghead

If anybody has some any other ideas to try I'm willing to listen. All tests were done with the hubs locked manually.

If I were you I would spend 15 bucks and replace both relays. I had a similar issue and I put two new relays in. Cleaned every electrical connection. And now my 4wd works mint. I don't think it is your motor because it has worked. But maybe your motor is the one making squealing noises. When I say motor im talking the electric motor for the t-case. And if the motor is bad my parts store had one for 81 bucks.

Just what im thinking, bringing anything to the stealership is gonna be painful to your wallet

Do most suggest buying the relays from the dealer or is NAPA a okay alternative?

Where are the 2 transfer case relays on my april 98 built 99 sd7.3? is the pn of the relays F0AB-14B192-AA? I am currently using a 14mm wrench on the selection shaft of xfer case, its getting kind of rough in -10C.

In this 2 relay box. You may have another two relay box closer to the firewall. They are the tow package relays for trailer battery charge abd trailer back up lights. If they are 4 spade relays they are not interchangeable with the 5 spade ESOF relays. If they are 5 spade then you can swap them.

https://www.ford-trucks.com/forums/a...9&d=1255902728

Well I replaced those two relays and installed my actuator motor and still no joy. I'm looking at the GEM now as the dash sw has been checked and it changes resistance like it should. Everything checks OK other than the GEM and from the schematic, it looks like it is a key player....thanks for the location help Robin

That's what mine is pointing to also. Just waiting for a check to arrive and ill be taking it in. I will post the end diagnosis once it's figured out.

:-bangheadWell my trucks 4WD hasn't worked for almost 10 months now. I tried all summer long to get it to work. I spent a whole Saturday, a couple of weeks ago, trying to get it working. I cleaned connections, polished relay posts, and attempted to engage it probably 30 different times (moving, sitting still, hubs locked in/out, in neutral, park, reverse, brake on, e-brake on, etc.) and nothing worked. So I decide to take it to a shop. Would you believe that they put it up on the rack and it turned the switch and it locked in first time!! WTH! It was dead. I was getting nothing and the day I take it into the shop it works. They pulled the GEM and it was "clean and like new." They checked the relays, and transfer motor and all the other stuff. The tech said he's miffed. He suggested I NOT replace the GEM. Not sure where to go from here. I'm confident it's going to happen again, when I need it most. Story of my life. The shop I took it to is a reputable one that specializes in Diesel especially, Fords. Oh, they also said there were no codes stored. :-banghead

one question if I put my locking hubs in manually then what do I set the 4 wheel drive mode switch too?I just done the guzzle Locking hub maintenance on them.thanks george

The ESOF switch needs to be used to shift the Transfer Case to either 4X4 High or 4X4 Low.

If the auto hubs are woorking correctly they should lock in the Auto position. The Lock position is for when the auto hubs do not lock automatically.

Here is some Ford Service Manual info:


Principles of Operation — Electronic Shift on the Fly (ESOF)
Transfer Case


The four-wheel drive electronic shift on the fly feature electrically shifts the vehicle transfer case between 2WD, 4X4 HIGH, and 4X4 LOW.

The system mode is selected by the operator through a three-position rotary switch on the instrument panel. The operator is informed which mode the system is in by two cluster indicator lamps, one for 4WD HIGH, and one for 4WD LOW (in 4WD LOW, both the lamps are on). Shifts into 4X4 HIGH can be made at any speed.


When shifting into or out of LOW range, the generic electronic module (GEM) requires that the vehicle speed be less than 5 km/h (3 mph), the brake applied, and the transmission in NEUTRAL (A/T) or the clutch pedal be depressed (M/T). (The digital transmission range (TR) sensor informs the GEM when the transmission is in the NEUTRAL range position.)


The electronic shift motor is mounted externally on the transfer case. It drives a rotary cam which moves the mode fork and the range fork within the transfer case between the 4X4 HIGH, 4X4 LOW, and 2WD range positions.


The 4X4 shift motor uses two relays which, under control of the GEM, shift the transfer case shift motor between 4X4 HIGH, 4X4 LOW, and 2WD modes.





The GEM accomplishes shifts system modes by interpreting inputs from:

1. 4X4 selector switch.
2. Vehicle speed signal (transmitted from the ABS system).
3. Transfer case.
4. Brake switch.
5. Digital transmission range (TR) sensor (automatic transmission).
6. Clutch pedal position switch (manual transmission).
7. Ignition switch.

Based on these inputs, the GEM controls the shifts into 2WD, 4X4 HIGH, or 4X4 LOW with the following outputs:

1. Low to high relay.
2. High to low relay.
3. Vacuum hub lock solenoid.
4. Transfer case shift motor.

The ESOF system has a feature which allows the driver to override the vacuum operated hubs. When the front hubs are manually turned to the LOCK position, the hubs are locked at all times, overriding the vacuum operated system. If the front hubs are manually turned to the AUTO FREE position, the hubs can only be locked by turning the 4WD mode switch to one of the 4WD positions.If the front hubs are unable to be unlocked by use of the 4WD mode switch, the hubs may be unlocked by turning the manual locking hub from the AUTO FREE position to the LOCK position and back to AUTO FREE.

Thanks for the information

More info. 1999 covers up to 2001 and 2002 also covers 2003.

Payson, now I think I understand the basic of the system. Seems like my 2000 works very well. I always heared people talk about ( true 4 wheel drive with the manual locking hubs ) so I just assume that they excursion worked that way. But with the information you gave me I now know it isn't. Thank you and merry Christmas George

Thanks everyone! This thread helped me finally figure mine out.

7 years ago, after the twins were born, I got a nearly-new '04 Excursion for my wife. We live in the mountains - steep grades and lots of snow. 2WD worked. 4H also worked, but only with hubs on manual. What "Auto" meant on those hubs was beyond me. In winter, we just kept it on "Lock". I never could convince myself it would go into low range. I joked with friends that Ford put the knob on the dash for "sales purposes only", and there really was no low range, since Ford designed the Excursion only for trips to the grocery store and soccer practice.

I once got a little "stopped" when I couldn't back up a steep grade to turn around in high range, and (as far as I knew), didn't have a low range on the thing (or a clutch).

Then somehow it once got into 4Low, and I couldn't get it out. This was 1.5 years ago. Tried rolling, stopping, backing-up, re-starting, pulling the "smart-key" in and out, etc. We were hitting the highway for vacation, and we were locked in 4Low. I was at an off ramp on the interstate, crawling around under the thing, wiggling wire connections and banging on the electrical shift motor on the transfer case with a big rock to try to loosen whatever was jammed. Whole family on-board. I was in a frenzy. Not sure what happened, but suddenly it was in 2WD again, and we were on vacation.

Then, earlier this week, I got my '73 dump truck stuck in the snow and needed to pull it out. The heaviest 4WD with good tires we have is the Excursion, so I grabbed that. Without knowing what I did, I somehow got it (for the second time in 7 years) into 4Low and pulled out my dump truck. I was briefly happy, but then I couldn't get the Excursion out of 4Low again. I shut it off hoping "time would heal". Today, my wife needed to take the Excursion to town for groceries, and had to do the 25 mile round-trip in 4Low. I again tried everything I could think of (except the big rock, which I never really thought was what made it work the previous time) and could not get it to disengage from 4Low.

I spent 3 hours ripping apart my dash-board and crawling on the ice under the rig this evening trying to diagnose it. Got the dash switch figured out and it seemed to work, but even hot-wiring the leads wouldn't budge anything at the T-case. I kept thinking to myself that if I cross the wrong leads, I'll fry the brain of the truck and have nothing left (as I did once on my 1990 F150), but by carefully checking resistance and voltages before making connections, I avoided this disaster. Fingers numb underneath the thing in 10-degree weather and the dark of night, and I could not get any indication that the T-case switch motor worked. With a 2-wire plug at the bottom of the motor unit and a 4- or 5-wire plug at the top, there was nothing obvious about how this thing worked. I came in the house half-frozen and resolved to go online, buy an electronic switch motor, and hope installing that would solve the problem.

Once online, though, I checked here and found this thread. Viola!

Motor running, in "neutral", foot on brake, and it switches between 2WD, 4H, and 4L fine. Just fine.

I'm sure it says to do this somewhere in the owner's manual, but I never found it. 7 years and finally it works for me. I'm feeling a little stupid...in a way.

I'm 49 years old and have owned 4wd trucks all my life. I currently have 9 of them and I've had at least 6 others in the past. From my experience, I am convinced there are 4 things all 4wd trucks should have:

1) Stick shift/clutch
2) Manual hubs
3) Lever-action T-case (my '56 Willys has 2 levers - I prefer having only 1)
4) Crank-windows

Today's "learning experience" has not changed my mind on any of these. Sadly, today's "truck" manufacturers don't agree with my 4 items of necessity.