What All Does the GEM Control?

FordandPolaris · Jan 8, 2013

Okay so we picked up a 2000 Expedition for my mom a couple weeks ago and it has many odd electrical faults. I am wondering if anyone can point me to a thread that might tell me what exactly that GEM controls. Google hasn't pointed me to anything of much help. I am confident that it is the cause of some of our various problems (some door locks do not work, some windows act funny, windshield wipers are psycho on start-up) but today she called my dad complaining the oil light was on and the gauge on L. Obviously not good, so he had her pull over and restart the truck after checking the oil. Oil is full, and gauge came back on. I realize it could be oil sending unit etc. as well as a bad solder on the back of the dash, but any additional info people have regarding the GEM would be quite helpful.

stamp11127 · Jan 8, 2013

These are a few of the inputs/outputs:
Defrost Relay Ground
Park/Headlamps On input
Interval Delay Input
Park Sense
Wiper Hi/Lo Relay
Run/Park Relay Control
Windshield Wiper Mode Select
Front Washer Pump
Door Ajar Indicator
Seat Belt Indicator
Left Front Door Ajar input
Left Rear Door Ajar input
Right Front Door Ajar input
Right Rear Door Ajar input
Lift Gate Door Ajar input
Illuminated Entry Input
Brake Pedal Position Input
Low Range output to PCM
Hall Effect Power
Rear Speed Sensor Input
4x4 Mode Switch
Torque on Demand Relay
Front Speed Sensor
AWD Engaged Output
Neutral Sense Input
ABS Active Input
Rear Washer Pump Control
Low Washer Fluid Lamp
Rear Wiper Hi/Lo/Park Sense
Rear Wiper Up Relay Control
Rear Wiper Down Control
Rear Wiper Switch Control
Washer Fluid Level Switch
Courtesy Lamps
Power Windows
Instrument Cluster
Anti-Lock Brake System
All Wheel Drive
Safety Belts
Ignition key Warning
Restraints Control Module
Rear Window Defrost

and I'm sure there are a few that I've missed.....

FordandPolaris · Jan 8, 2013

Oh that is awesome, thank you very much for posting that up. That should help out a lot. Her all wheel/A4WD has been acting really weird too, I am glad that could possibly be tied to the GEM as well.

stamp11127 · Jan 8, 2013

If you choose to replace the GEM you may also consider making a small test. Since water has been the main problem with these try placing it in your clothes drier on the shoe rack if it has one. The low heat setting will work best. Most modern electronics have a wax like coating on them for protection, all you need to do is remove the moisture from the inside. After it has "cooked" a few hours give it a shot after it has cooled off.
I've used this procedure in the past with good results, a few times the damage was more than just water and it hasn't worked fully.
If this does work for you, let us know. We have a spray for electronics at work that supposedly repels moisture. Never had to use it though, so don't know how well it works. I will give you the brand name should you want the extra protection.

FordandPolaris · Jan 8, 2013

We dont have a shoe rack in our drier, and I cant imagine it tumbling around will produce usable results haha. However I can probably achieve the same effect by putting it in the oven at low temps. We will probably replace it with a new one anyways since they are relatively cheap (ebay has them for around 90 bucks which isn't bad) but I might try and dry out the old one simply for forum use. I will update this thread when we get around to doing it.

toms89 · Jan 9, 2013

FordandPolaris said:
We dont have a shoe rack in our drier, and I cant imagine it tumbling around will produce usable results haha. However I can probably achieve the same effect by putting it in the oven at low temps. We will probably replace it with a new one anyways since they are relatively cheap (ebay has them for around 90 bucks which isn't bad) but I might try and dry out the old one simply for forum use. I will update this thread when we get around to doing it.

I had considered doing this but used my neighbors pellet stove instead. Set it along with the fuse block close to it for 24 hours. Reinstalled and have not had issue since.

Think the oven idea would work fine if you keep it on its lowest setting and closely monitor it. Actually had an "air adjuster" (electronic device for adjusting mass air signal) for my stang that recommended using the oven method to dry it if it got wet. Guess worse case you have to replace gem?!

toms89 · Jan 9, 2013

stamp11127 said:
These are a few of the inputs/outputs:
Defrost Relay Ground
Park/Headlamps On input
Interval Delay Input
Park Sense
Wiper Hi/Lo Relay
Run/Park Relay Control
Windshield Wiper Mode Select
Front Washer Pump
Door Ajar Indicator
Seat Belt Indicator
Left Front Door Ajar input
Left Rear Door Ajar input
Right Front Door Ajar input
Right Rear Door Ajar input
Lift Gate Door Ajar input
Illuminated Entry Input
Brake Pedal Position Input
Low Range output to PCM
Hall Effect Power
Rear Speed Sensor Input
4x4 Mode Switch
Torque on Demand Relay
Front Speed Sensor
AWD Engaged Output
Neutral Sense Input
ABS Active Input
Rear Washer Pump Control
Low Washer Fluid Lamp
Rear Wiper Hi/Lo/Park Sense
Rear Wiper Up Relay Control
Rear Wiper Down Control
Rear Wiper Switch Control
Washer Fluid Level Switch
Courtesy Lamps
Power Windows
Instrument Cluster
Anti-Lock Brake System
All Wheel Drive
Safety Belts
Ignition key Warning
Restraints Control Module
Rear Window Defrost

and I'm sure there are a few that I've missed.....

Damn!!

Nice list....lol.

To sum it up pretty much everything other than the engine and transmission functions which is controlled by the pcm. The main items of interest are the A4wd and interior systems. There are other modules but they are monitored and/or controlled by the gem.

FordandPolaris · Jan 12, 2013

Sorry for the late reply but this is good stuff. We will probably just go ahead and replace the GEM with a new model. Better to have the peace of mind. Is there anything I should know about installing a different GEM into the truck or is it just like anything else, plug it in and it does what it needs to do automatically?

eastmonsoon · Jan 31, 2013

With the GEM you must take it to a dealer to have it re-programmed. I have replaced one and am now going to "bake" it after I thought I had the leak fixed and it "freaked out" again. It also controls the starter motor. Mine will occasionally start itself if the key is in the on position and in park or neutral, even when running. Ouch!

stamp11127 · Jan 31, 2013

Eastmonsoon, I checked back through the wiring diagram for my 99. They do not list any GEM circuit that controls engine starting. The only thing that is close is the "ignition key warning switch". I looked at the diagrams and the connector pin outs for anything starter related.

Your intermittent starting issues are probably caused by something else.

Update:
After looking at another problem there is an input connection to the GEM prior to the Trans Range Selector - which just happens to be a branch circuit of the starter. But doesn't appear to control the starting.

toms89 · Jan 31, 2013

Edit: The following applies if you feel moisture in the gem was a possible source for your issues.

I would highly recommend if you replace the gem module you remove and make sure the fuse block in which it piggybacks is completely dry inside.

I say this because when I had issues I really did not notice much if any water in the gem module itself but a fair amount did pour out of the fuse block when removed.

I believe this is due to the design and angle. The gem will tend to drain better. The fuse block is located below and it appears to hold water well. Once you find the assembly you will understand how all the water goes right there. Its because the wiring harness is going down hill right to it. Any water behind the dash follows the wires right to it.

I assume that since the gem controls and monitors various circuits through the fuse block it could have adverse effects on it?!

So again I would recommend pulling the fuse block while your there and drying it out near a source of heat. I set mine near a pellet stove overnight as well as my gem module.

bojaz01 · Feb 25, 2013

where on ebay did you find a gem for $90.00? if you dont mind me asking....ive got the same problem on occasion....gauges acting all squirrelly and such....gonna have my windshield checked for leaks before i do anything though......

radar · Apr 18, 2013

How about the cruise control?
Have tried everything else clock-springs, buttons & servo.
Still doesn't work, press on/off & any other switch & the horn blows!

toms89 · Apr 18, 2013

radar said:
How about the cruise control?
Have tried everything else clock-springs, buttons & servo.
Still doesn't work, press on/off & any other switch & the horn blows!

That's too funny !!

Sorry.... I would probably be looking for a short in the steering column but it sounds like you have already been there.

radar · Apr 19, 2013

Yep! Sure have. Looked over wire harness for any damage but haven't any let.
I hope someone can give me a clue.

stamp11127 · Apr 19, 2013

I would pull the "speed control switch" assembly in the steering wheel and test the connections.

There are internal resistors for the different settings:
On - 1000 ohms
Resume - 2200 ohms
Set/Resume - 680 ohms
Coast - 120 ohms

Hot wire coming in to the speed control switch is the DB colored wire,

If any of them are at or close to 0, when you press the on and any of the others you have an almost direct path to ground through the speed control servo. You may hear a slight difference in the horn with On & Resume switches.
If the switch passes the test I would test the wires for a short to ground. Disconnect/remove the air bags prior to testing - the dvm will trigger them.

Does your horn work with the horn switches?

stockd15b · Sep 10, 2013

sorry for bumping an old thread. Would it be possible to drill a hole in the GEM, check for moisture and then fill with thermal conductive epoxy, to prevent any from entering?

FordandPolaris · Sep 10, 2013

stockd15b said:
sorry for bumping an old thread. Would it be possible to drill a hole in the GEM, check for moisture and then fill with thermal conductive epoxy, to prevent any from entering?

Possible sure, but no idea how it would affect it. Worst case, it does not work and you replace the unit anyways (assuming you are seeing problems). Though I would have the new one on hand and ready since no accessories will work in the truck without it.

Replace the windshield seal, or the windshield itself, and depending on how bad your problems are, they will disappear as it dries out on its own. That is how mine ended up.

handyone · Sep 26, 2013

What does "GEM" stand for & where is it located in my '04 EB?

FordandPolaris · Sep 26, 2013

General Electric Module. It piggybacks to the fuse block below the driver's side dash. Are you having electrical issues? Most GEM issues occur in the 1st gen expy's but doesn't mean it couldn't happen to the 2nd gen.

Do you get wet floors on the inside after a heavy rain?

What All Does the GEM Control?

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