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Replacement GEM module 1997 AWD 4.0L SOHC?

pcrussell50

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socal
Year, Model & Trim Level
1997 expolrer xlt
Had this car since my parents bought it new in 1997. They are old now and don't drive anymore so the wife and kids and I have it as a spare car that we use only every so often. Well the a few days ago, the transfer case went out (it went out once before, 12 years ago), and in this AWD version, when the t-case goes, all drive goes, not just the front.

The transmission and gear shop just called. The fixed or replaced the t-case, but told me the GEM (transfer case control module) is faulty and they can't get one from Ford or their usual sources. They tested the AWD actuator motor and it was good. And they said it's throwing a code pointing to the GEM. They said I could almost certainly get one from ebay but they don't deal with ebay themselves, so I will.

What I want to know is two things:

1) how much do I have to tear apart the dash to r and r the GEM?
2) if i do, do i have to reflash it or will the PCM see the GEM without a flash?

-Peter
 



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Gem is right behind the radio, 10 minute job.
I'm pretty sure it's plug and play but maybe someone more knowledgeable here can clarify.
 






Thanks friend. The tranny shop thought it was plug and play too, but they weren't sure. So that's two votes of confidence on this. Good news about the easy r and r job.

-Peter
 






Seems fishy, too coincidental to me. Transfer case goes out and GEM goes out right when they're working on it? I mean if ONLY the GEM went out, that I could see causing a different problem of not shifting into 4Low, 4High, or engaging front in A4wd, WITH a transfer case that's fine still, but not needing to "fix" the transfer case and need the GEM too.

I know less about the AWD setup, but from your other topic posts it looks like you have the 4.0L SOHC engine which means you don't have AWD, instead 4WD with an electronic clutch.

What trouble code is showing up? Is it possible that this was only due to the transfer case failing and it merely needs the code reset? Mechanically, operationally driving it, what isn't working? Originally when you took the vehicle to them it wouldn't move, but now what state is it in?

AFAIK, the Shift Control Module, which I assume is what is meant by "transfer case control module", is not the GEM, rather a couple relays so two separate things. I suppose it could be that this shop is honest and knows what they are doing, but something got lost in communication about the situation.
 

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  • transmissions-4wd-circuit-1-of-1.pdf
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Well, it's for sure the transfer case went out. When it goes out on this system, you get no drive at all, front or rear. As opposed to a more traditional 4wd system where if the tc goes out, the rear still drives but you lose the ability to drive the front. The same thing happened 12 years ago. New tc fixed it.

The system switch on our XLT has "auto" "4wd hi" and "4wd lo". In "auto" if the wheel speed sensors detect rear axle wheel spin, the actuator motor on the tc engages the front wheels automatically. The other two settings lock it into 4wd all the time.

I'm picking up the car today. I will find out from them, the code that was pointing to the GEM. They told it to me, but I didn't write it down. They did read me the part number of the module that they say is bad, and when you look up the number, it is a GEM. I'll get the code and report back.

-Peter
 






Had this car since my parents bought it new in 1997. They are old now and don't drive anymore so the wife and kids and I have it as a spare car that we use only every so often. Well the a few days ago, the transfer case went out (it went out once before, 12 years ago), and in this AWD version, when the t-case goes, all drive goes, not just the front.

The transmission and gear shop just called. The fixed or replaced the t-case, but told me the GEM (transfer case control module) is faulty and they can't get one from Ford or their usual sources. They tested the AWD actuator motor and it was good. And they said it's throwing a code pointing to the GEM. They said I could almost certainly get one from ebay but they don't deal with ebay themselves, so I will.

What I want to know is two things:

1) how much do I have to tear apart the dash to r and r the GEM?
2) if i do, do i have to reflash it or will the PCM see the GEM without a flash?

-Peter

Probably just miscommunication, but there is no electronics associated with the AWD transfer case - it's purely hydraulic. If your Ex is 4.0L, it's 4WD, not AWD. And in that case, the transfer case is electronically controlled, but not by the GEM; at least not directly.
 






Well both of you seem to have corrected me that I don't actually have AWD, but rather automatic 4WD. I wasn't aware of the difference. I assumed "automatic 4wd" was the same as AWD. Thanks, guys.

I also read back to one of my old threads... The motor actuator on the tc apparently is only for engaging low range, NOT for engaging 4wd. And the GEM reads the front and rear output shaft speed sensors and sends torque to the front when it detects excess rear axle speed compared to the front. Sound right?

Here is the description of how the system works from another member here:
If you've got a switch knob on the dash you have Automatic 4WD.

There are two Hall effect speed sensors on the transfer case. 1 each on the front and rear output shafts.

The flashing 4Hi/4Lo lights is the system telling you it's not getting a signal from the sensors which it wouldn't with the connector unplugged. That's because the speed sensor wires are in the connector to the shift motor.

This part gets confusing.

The shift motor doesn't actually put the case into 4WD, that's accomplished by an electromechanicall ball ramp clutch in the case controlled by the GEM (Generic Electronic Module)

In Auto mode the speed sensors detect a speed difference, send the difference signal to the GEM, and the GEM engages the clutch.

in 4Hi the switch sends a signal to the GEM you want 4Hi to stay on and the GEM sends a signal to the clutch regardless what the speed sensors on the output shaft are telling it about axle speeds.

In 4WD Low Range, the transfer case electromechanical clutch locks the front and rear driveshafts for maximum 4WD traction. The transfer case motor also rotates the shift cam to move the reduction fork to the 4WD low range position. This low range shift is accomplished through a planetary gear set which changes torque to the driveshaft from 1:1 to 2.48:1 ratio.

Clear as mud isn't it. It took me a while to wrap my head around this when I went looking for the cure to my problem.

My thought is you've likely got a bad front output speed sensor. Either completely dead or not accurate. The GEM thinks the rear wheels are turning faster than the front and engages the ball clutch. Or you've got a wiring problem.

-Peter
 






Yes a difference in shaft speed sensor output will engage front wheels progressively more and more until the speed sensors are the same, when in Auto, A4WD mode. If one of the sensors isn't working that will trigger a trouble code, not engage the front shaft. With the dash switched to 4WD Hi, the same electronic clutch just stays 100% engaged.

IF that is what isn't happening then you can measure for 12V on the brown wire going to the transfer case, should be constant 12V (or nearer 14.4V engine running) with it in 4WD Hi. If no voltage on the brown wire then something upstream isn't working.

If voltage on the brown wire but it's not engaging the front wheels then something is still wrong in the transfer case. Error codes, I would clear them and see what returns.

You don't necessarily need a code to figure out a problem with this though if it's the shift motor for 4Low instead, a code might narrow things down faster.

I am skeptical that the shop damaged something while working on it, or didn't get the transfer case completely fixed... one or the other, unless the only thing left to do is clear the code and it's all 100% now.

It would be good to get a complete description from the shop, exactly what they did, and if they just swapped in a different used transfer case, it could have a problem.
 






Just a heads up...

Finding a GEM with matching part numbers to your might be difficult in the junkyard. When I thought I was having a GEM problem, I looked through a lot of 95-97s in one junkyard and only found one. If I recall correctly, it is not easy to read the part number unless you remove it, or take a pic of it with your phone. I think the first one I looked at, wrong number, I just removed it just to see how easy/difficult it was.
 






Just a heads up...

Finding a GEM with matching part numbers to your might be difficult in the junkyard. When I thought I was having a GEM problem, I looked through a lot of 95-97s in one junkyard and only found one. If I recall correctly, it is not easy to read the part number unless you remove it, or take a pic of it with your phone. I think the first one I looked at, wrong number, I just removed it just to see how easy/difficult it was.

Did replacing the GEM fix your 4wd problems? I found one on eBay with a slightly different part number and it description was a grid listing the different vehicles it's good for, and my year make model and engine was one of them.

-Peter
 






I am skeptical that the shop damaged something while working on it, or didn't get the transfer case completely fixed... one or the other, unless the only thing left to do is clear the code and it's all 100% now.

It would be good to get a complete description from the shop, exactly what they did, and if they just swapped in a different used transfer case, it could have a problem.

You read my thread from 2012 I think. That shop was a hack general repair shop that does a bangup job on brakes shocks and air conditioning and replacing sensors. I'm not at all sure they didn't mess something up, though it worked fine for the last six years (never using 4wd).

This repair shop today is the gear shop all the hot rodders go to. And all they did was rebuild the transfer case so I could drive the car home. They told me they could not get it to go into 4wd. And that the GEM is what tells it to go into 4wd (either if you select it or in auto mode).

Is the brown wire available for access near the GEM? (Behind the radio)

Also, I can hear the low range motor actuating and de-actuating when I shift into N and select and de-select 4 low.

-Peter
 






^ Yes, behind the radio. There are pictures and info in this topic:
How to: - The Comprehensive Brown Wire Mod Thread

If you look at that diagram I attached previously, the brown wire runs between the TOD (torque on demand solid state relay) and the transfer case connector for the 4WD magnetic clutch coil.

If you don't have 12V on the brown wire when switched to 4High mode, check to see whether there is voltage on the TOD yellow (or is it yellow/brown?) wire. If there is, the TOD is probably blown (assuming no wire or connector problems).

If there is not, the GEM is not outputting this control voltage to the TOD (again assuming no wire or connector problems).

What remains is to check the resistance between the GEM gray/red and the white/light-blue wires as you change the Auto/4H/4l SWITCH, at the switch or at the GEM, or ideally both to make sure that's a good connection. You can see on the diagram that it should vary from roughly 3.9K to 1.1K to 360 Ohms. If it does not, the switch (or again the wire or connector) is bad. If it does, the GEM seems bad.

You could also cut the brown wire and on the end going to the transfer case, tie it to another 12V source to see if 4High engages. I don't know how much current the coil needs but it shares a 30A fuse with windows, seats and moon roof. I'd want at least 15A available on anything you would tap into to test it, more if possible. The cigarette lighter outlet power feed is what I'd pick, since it is non-essential to anything else. I mean only for testing since IIRC it stays live when the ignition is off. I'd put a temporary switch between it and the brown wire then switch it on for testing once on the road..
 






Did replacing the GEM fix your 4wd problems? I found one on eBay with a slightly different part number and it description was a grid listing the different vehicles it's good for, and my year make model and engine was one of them.
-Peter

Whatever problems I had, which I cannot remember, the GEM was not the issue.

What is your part number that you are looking for?
 






^ Yes, behind the radio. There are pictures and info in this topic:
How to: - The Comprehensive Brown Wire Mod Thread

If you look at that diagram I attached previously, the brown wire runs between the TOD (torque on demand solid state relay) and the transfer case connector for the 4WD magnetic clutch coil.

If you don't have 12V on the brown wire when switched to 4High mode, check to see whether there is voltage on the TOD yellow (or is it yellow/brown?) wire. If there is, the TOD is probably blown (assuming no wire or connector problems).

If there is not, the GEM is not outputting this control voltage to the TOD (again assuming no wire or connector problems).

What remains is to check the resistance between the GEM gray/red and the white/light-blue wires as you change the Auto/4H/4l SWITCH, at the switch or at the GEM, or ideally both to make sure that's a good connection. You can see on the diagram that it should vary from roughly 3.9K to 1.1K to 360 Ohms. If it does not, the switch (or again the wire or connector) is bad. If it does, the GEM seems bad.

You could also cut the brown wire and on the end going to the transfer case, tie it to another 12V source to see if 4High engages. I don't know how much current the coil needs but it shares a 30A fuse with windows, seats and moon roof. I'd want at least 15A available on anything you would tap into to test it, more if possible. The cigarette lighter outlet power feed is what I'd pick, since it is non-essential to anything else. I mean only for testing since IIRC it stays live when the ignition is off. I'd put a temporary switch between it and the brown wire then switch it on for testing once on the road..

I almost forgot, the code the guys at the shop gave me was (B1867), but when I googled it, it came out as "PCM/module short to ground" the shop guys think it was the GEM. If it really was the engine control you'd think the engine would not run right. But it runs fine.

Took it for a comprehensive test drive today.
1) the rotary auto/4H/4L switch works as far as illuminating to 4H and 4L lights in the dash, (have not checked resistances). and it turns the transfer case to low range as it should, verified by hearing the low range motor turn, and test driving where it's in top gear by 15mph and doing over 3000 rpm on 25mph neighborhood streets.

2) as the shop warned, I'm pretty sure 4wd is not working because even in 4L, tight turns produce no scrubbing, like it used to when you were in 4wd on dry pavement.

So, low range will engage as it should, and 4wd does not. And the rotary switch illuminates the dash lights as as it should.

Anything we can tell from this, without checking the brown wire or the TOD wire? Before I dig up the multimeter?

-Peter
 






It doesn't give me any new ideas so I'd break out the multimeter, paying extra attention to wiring faults in case a short means a damaged wire.
 






It doesn't give me any new ideas so I'd break out the multimeter, paying extra attention to wiring faults in case a short means a damaged wire.

Ok. It is what it is then. Going away with the wife and kids for spring break, but I will get back to this then. Thanks a bunch for the guidance so far. It has been a big help. Especially the link to the brown wire mod, with it's helpful pics. :thumbsup:

-Peter
 






I almost forgot, the code the guys at the shop gave me was (B1867), but when I googled it, it came out as "PCM/module short to ground" the shop guys think it was the GEM. If it really was the engine control you'd think the engine would not run right. But it runs fine.


-Peter

I don't know how I missed this before but B1867 comes up as an airbag code not a drivetrain code. I would want to talk to the guy who wrote down the code and made the connection to the transfer case, to hear his argument for what is going on if that's the right code.

Then again... I could be wrong. Something still seems fishy but it's hard to smell fish across the internet. ;)

If this were something important like your health then I'd recommend to go to a different doc for a 2nd opinion.
 






If you don't have 12V on the brown wire when switched to 4High mode, check to see whether there is voltage on the TOD yellow (or is it yellow/brown?) wire. If there is, the TOD is probably blown (assuming no wire or connector problems).

If there is not, the GEM is not outputting this control voltage to the TOD (again assuming no wire or connector problems).

Fishy stuff abounds. Back in 2012 when the car was permanently locked in 4wd, the hack shop did all kinds of stuff to "fix" it. It is clear that they went behind the dash. screws missing. some grinding done on plastic pieces around the vent outlet. the TOD looks like the older kind in the Gen1 ControlTrac that ended in 1996. My1997 should be a Gen2 Control Trac. The GEM does not have an F7xxx... number on it, etc... Could it be an aftermarket? Or a junkyard piece that looks right, but isn't? I has grease pencil writing on it like some junkyards do to catalog parts. Eventually they "fixed" it so that it was not permanently in 4wd, no matter the switch position. That was from back in 2012.

Fast forward six years, when it lost all drive capability. The recent shop, the gear specialists, all they did was rebuild the transfer case so the car could at least drive again, and test the 4wd, and tell me it was not working. They did no fiddling behind the dash... or if they did, I did not ask them to, and they didn't charge me for it. Their first thought is that the reason the 4wd is not working is a bad module. Could always be a wire or connector, but the wires look pretty unmolested.

But back to nuts and bolts, the TOD has a nice fat yellow wire in it's pigtail, and a nice fat brown wire. Can I use those to probe for 12v? or do I have to break the brown wire out of the bundle behind the GEM to get a valid brown wire test? I'm guessing the former.

-Peter
 






The problem with people changing things from stock parts is you are left guessing what they had to do to make it work. Similarly who knows what wiring is there now...

If they didn't mess with the wires then yes you can probe for 12V on the brown wire at the TOD - with the dash switch in 4High position. That brown wire does not go to the GEM, just between the TOD and the transfer case coil. It must be plugged into the TOD to have 12V on it.

TOD_Transfer-Case.png
 



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I just checked. It doesn't look like they spliced in an older TOD. The wiring all around it looks totally unmolested. No splices of any kind. Maybe my 1997 Explorer used an older style TOD relay because maybe the older TOD relay would still work for newer ControlTrac? :shrugs:

What I can say is that the GEM looks like it might be aftermarket simply because it doesn't have an F7xxx.... number. Interestingly, the shop that did the transfer case gave me a proper number in case I could find one and wanted to replace it: F77Z14B205BD which checks as a GEM for my year Explorer.

Thanks again for bearing with me and responding to my questions. In a couple of hours I will be leaving for vacation. I might ask a question or two if I think of them. But otherwise I will be back with voltage test results in a little over a week.

-Peter
 






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