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No 4WD and no dash light

38K views 48 replies 4 participants last post by  tykesplace 
#1 ·
I'm sure this is related to the issue I had this summer when my trans/transfer case wiring harness dropped onto the front drive line while my hubs were stuck and the harness got torn up. Yeah it was a ****ty day. Anyway I cleaned it up, soldered in, and shrink tubed the wiring repairs. I'm feeling confident that the wiring repairs are good. It was summer and I didn't think about checking the 4wd.

Well now it's snowing and I find that I have no 4wd. No light on the dash even. I understand about checking the t-case motor for voltage, but if that's the problem should the dash light still work? I replaced the two under-hood relays in July, and the fuse is good. But some of the wires did short out to the truck. Maybe the wires shorting out fried a relay, the motor, or the GEM? Just wondering before I start replacing stuff, what component could have gone bad that would make the dash light not work?

Was going to go hunting this weekend too. Might have to skip that.
 
#2 ·
When my GEM burnt I could smell it if I got down by the fuse panel. I isn't too bad to get to but usually other options like power door locks are effected at the same time. I soldered it and put superglue over that and it held. Not saying that's the problem, but it's a possibility.
 
#3 ·
The position switch on the t-case motor reports back to the GEM and it turns on the light on the dash. So the issue could be at the t-case or at the GEM. My guess would be at the t-case. It could be that the motor is fried and can't shift the t-case (and turn the position switch).
 
#4 ·
I didn't and don't smell anything. The windows and door locks work.

That makes sense about the light. It's not connected to the switch directly, it's responding to the t-case engaging. That's why the light doesn't come on right way going to 4LOW, because that takes longer to engage.
 
#5 ·
I just checked the two-pin connector to the t-case and get no voltage when moving the dash switch. Tonight I swapped the t-case relays with the other two right next to them but still no voltage with the switch.

Then I applied battery voltage to the motor's pins and I can hear the motor moving. Switch polarity and I hear it move again (back?). I don't know if it's putting the t-case in 4wd. However I get no dash light in either case.

Not sure what to check next.
 
#6 ·
I just checked the two-pin connector to the t-case and get no voltage when moving the dash switch. Tonight I swapped the t-case relays with the other two right next to them but still no voltage with the switch.

Then I applied battery voltage to the motor's pins and I can hear the motor moving. Switch polarity and I hear it move again (back?). I don't know if it's putting the t-case in 4wd. However I get no dash light in either case.

Not sure what to check next.
When you put battery power it is probably switching the motor, but no signal is going back to tell it to turn on the dash light. Did you have power to the switch? Is there power to the relays?
 
#8 ·
What year is your truck?

Post that and I'll dig up a wiring diagram for the ESOF to help you troubleshoot.
 
#10 ·
I just had a thought. The voltage at the two-wire connector. Are both hot, just at different times depending on which way the motor being turned? When I checked voltage it was across those pins. If both are positive but only hot one at a time, I don't think I would read volts, correct? Should I instead test positive with the multimeter on each pin separately with negative to a ground?
 
#11 ·
The two relays work together to switch polarity of the two wires powering the shift motor. One connects to ground, and the other connects to 12V. They may just both be grounded normally, and the one or the other pulls in to supply 12V to the motor to run it in either direction. So putting your meter probes in both wires should work, or you could put the black probe on a ground point.

I'll get that wiring diagram to you a bit later tonight after I get home.
 
#12 ·
#13 ·
Thanks for the diagram. Very helpful. It's looks like the GEM is right in the middle of everything.

Here's what I see with the t-case shift relays on Page 1. The diagram says "the t-case shift relay controls the operation of the t-case from L2H and H2L through inputs from the GEM". Both the Low/High and High/Low relays have 5 pins each.
  • Pins 85 and 87 are DG/LG from the dist box, fuse 17, and should be hot. So I'll check those to make sure power is coming in.
  • 87A should be to a good ground.
  • Pins 30 are O and Y wires to the t-case motor, but only look to be hot if activated at the relay. Otherwise they're ground. If I test continuity from those wires to ground that means the relays are in the position as shown in the diagram. I think these wires could have been damaged in my harness incident so I'll also check their integrity between the relays and the t-case motor.
  • Pins 86 are BR/W and O/LB coming from the GEM relay controls. I'm thinking these control the t-case relays and would only be hot if triggered by the GEM.
So do these relays only control L2H and H2L? Meaning the t-case motor doesn't move the t-case from 2WD to 4WD? Just between 4H and 4L when triggered by the GEM which responds to the 4WD mode switch? When I was stuck in 4L this summer I replaced these relays and could then get out of 4L, so that seems to be true.

Here's what I see with the 4WD mode switch on page 3. It is connected directly to the GEM and has Off/High/Low positions. I don't see how the GEM knows what position the switch is in though. Varying resistance in the switch position maybe? Also the GEM is connected to the t-case through the 7 pin connector. Is that how the t-case is moved between 2WD and 4WD? Again this is the harness that was damaged. And finally the dash indicator lights are hot from the dist box fuse 19 and are are triggered by the GEM.

So, even if I can confirm the integrity of all the t-case shift relay wires, the t-case motor, fuses 17 and 19, and the t-case relays, I think that only tells me about the mechanical functionality of L2H and H2L. Not 2WD to 4WD. Is 2WD to 4WD internal through the t-case contact plates as shown on page 3? Again these are connected to the GEM.
 
#14 ·
More info. I'm shopping around for a GEM just in case that's the issue and found this one at AutoPartsCheaper.com. I called a tech to make sure I was looking at the right one. I also asked about the 4WD functions. He confirmed that the t-case motor only engages/disengages 4L. Moving between 2WD and 4WD is engaged inside the t-case and is controlled directly by the GEM. He said this is why you don't feel anything when engaging 4H. Almost like a clutch. However 4L is a mechanical engagement triggered by the motor and therefore the clunk when going to 4L.
They're on back order for that part until March or so. I hope that I can find it somewhere else.
 
#16 · (Edited)
I called a tech to make sure I was looking at the right one. I also asked about the 4WD functions. He confirmed that the t-case motor only engages/disengages 4L. Moving between 2WD and 4WD is engaged inside the t-case and is controlled directly by the GEM. He said this is why you don't feel anything when engaging 4H. Almost like a clutch. However 4L is a mechanical engagement triggered by the motor and therefore the clunk when going to 4L.
That guy is WRONG. The motor (or single shift lever on the manual t-case) controls all the functions. The manual shifter is all the way forward for 2L, middle is 4H, and all the way back is 4L, (with neutral in between 4H and 4L), all done with the same lever. The motor works the same way.

The position switch controls the motor operation thru the GEM, by activating or de-activating the relays. The switch tells the GEM to engage the relay to start the motor and the switch tells the GEM when it's in the position selected and opens the relay to stop the motor.

And the switch does use different resistances to talk to the GEM.

I wouldn't change out the GEM till you confirm that all your wiring matches the diagram. It's possible that you didn't get everything reconnected right, or still have an open circuit somewhere.
 
#17 ·
So the shift motor has three positions? Looking at the diagram I don't see how that happens. On page 1 I see the L2H Relay and the H2L Relay both go to the transfer case shift motor. I don't see the t-case shift motor anywhere else on the diagram. The only wires going to the shift motor are the Orange and Yellow and they come from the L2H and H2L relays. Is there more inside that I can't see or that aren't on the diagram?

On page 3 it shows the switch going to the GEM, which in turn goes to the t-case contact plates A, B, C, D, and VCC. I don't know what those are. It also has leads to the brake pedal position and trans range sensor so you can only go in 4L with the brake depressed and trans in neutral.

Am I missing something? I will be testing wires tonight after work. Not sure I can get a GEM right now anyway. Every place I looked is out of stock.
 
#19 ·
So the shift motor has three positions?
The shift motor doesn't really have "positions". It just runs forward or backward. The position switch tells the GEM when to turn the motor off. Say you're in 2H, and flip the switch to 4H - The GEM starts the motor going toward LOW position, and the position switch tells the GEM to stop the motor as it gets to 4H. Same thing going in the opposite direction.

A, B, C, & D are the position switch outputs to the GEM, The VSS (Vehicle Speed Sensor) input is for going to 4L, telling the GEM that the vehicle is stopped, and it's OK to move to/from 4L. Similarly, the brake and tranny shift on position inputs restrict the motor from moving unless in neutral and brake is on, as you already figured out.
 
#20 ·
So the relays aren't just for H2L and L2H. They move the motor along all three positions. One relay moves the motor one direction, the other relay moves the motor in the other direction. The GEM reads the outputs from the transfer case and stops the motor in the correct position based on the switch position.
So I'm still left with confirming integrity of the wires, relays, and fuses. If those are good then the GEM is the only thing left. Correct? If so I might be up a creek. The factory is out on those until March and all of the places online are saying out of stock until then. Not really keen on getting one from a junkyard.
 
#21 ·
Yes, if you can confirm that everything is wired correctly and you check the actual function of the position switch (they can go bad also), then that pretty much narrows it down to the GEM.

I don't think that a wrecking yard GEM would be a giant risk, but that's up to you. You do have to get one that matches your year and trim level, and they need to be programmed to exactly match your truck. So I'd exahust all other possibilities first.
 
#23 ·
Well I've tested as best I could. The wires I tested have continuity. I hope I tested all the necessary ones. So I searched again for a GEM. The Ford factory parts are non-existant until March. I ended up ordering an A1Cardone unit. 30 day money back guarantee so I can return it if it's not the problem. If that doesn't do it I guess I have some more diagnostics, though I don't know what else I can check.

As an aside, while pulling the 7 pin connector from the t-case I broke the retaining clip. So I have the plug held tight with wire. Anyone know of source where I can purchase those types of plugs to patch in?

Also, the GEM matches my trim. ESOF, power windows, no keyless. Am I going to need it programmed by the dealer anyway?
 
#24 ·
I believe it's the GEM that takes care of speedo calibration, but I'll check that for sure later. You'll at least need to get that checked. Were you able to check the condition of the position switch? To do that, you'd have to remove it from the t-case and run it thru all positions while checking continuity thru the switch contacts at the terminals.

On the wiring connector, you can check with Ford for a matching pigtail. Here's the catalog:
http://www.fordtechservice.dealerconnection.com/Renderers/ie/wiring/svg/images/connectorcatalog.pdf
 
#26 ·
Here's the stuff the GEM needs to be programmed for (from the Ford service manual):
4WD ESOF
Overspeed Warning
Beltminder
Remote Keyless Entry (RKE)
Transmission Type
One Touch Down
Delayed Accessory
Brake System Configuration
 
#28 ·
The position switch has the 6-pin connector. You shouldn't have to remove the switch to test it if you can get your meter into the connector to probe individual terminals.
 
#30 ·
Continuity between pins as you move the switch. I think pin 4 ground on the diagram I posted would be common for your meter, and the other lead to each of the lettered terminals (1-D, 3-B, 6-C, and 5-A). Not sure about the VCC contact. I thought that was VSS (Vehicle speed sensor) previously. I'll have to dig a bit deeper and will post what I find out.
 
#31 ·
Took the truck and GEM out to the dealer this morning. $102 later and I get "Could not program GEM" with no error code. He said they could communicate with the original GEM to download its data, and with the new GEM, but just couldn't program it. They offered to do diagnostics for "maybe an hour, could be more" to determine what the problem is.
I'm going to give it another shot checking wire continuity, but I'm almost at a loss. Might have to have them handle it.
 
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