A relative of mine had a problem with their 2001 Ford Explorer that was
traced to something called the "GEM" module.
Some web-searching indicates that GEM stands for "Generic" or "General"
Electronic Module - yes?
Would there be any drive-ability or operational problems for the vehicle
if this module was dead or faulty?
Does it control any aspect of engine or drive-train operation?
Head or signal lights?
They had this fixed (I think the total cost was around $600 - parts and
One thing they mentioned is that a "satellite" was somehow involved with
the repair (not sure if they heard that right with the repair shop). Is
there any sort of remote telemetric configuration of the new module that
would involve a "satellite" connection? Does the 2001 ford explorer
have any sort of satellite receiver built into the vehicles electronic
This was a 4wd vehicle - don't know exactly what "version" of 4wd (if
there are more than 1, that is).
What about instrument cluster? Speedometer? Radio?
But they would still have manual control of headlights?
Can a GEM module be purchased and installed by a backyard mechanic - ie
without needing to program the new module?
Did 2001 ford explorers come with any chip or RFID-enabled key fobs?
Sentry Key, ignition module electronic theft prevention, etc, that would
require that the GEM module "learn" the owner's key-fob codes?
I'm not terribly familiar with the Explorer 4WD. I know my Dad's '98 had
some kind of automatic version that acted almost like it was full time,
but I'm not sure it was. There was a switch on the dash that selected
Auto, 4WD and 4WD low. The GEM module may very well have had a hand in
that operation in 2001.
I'm more familiar with F150 and F250 trucks, where the transfer case was
either engaged or it wasn't. The GEM in those with Electronic shift 4WD
took speed sensor data, clutch and brake position data, and the 4WD
switch input and controlled the transfer case shift motor and auto
locking hub solenoid.
The instrument cluster received information, either through one of the
data busses, or direct wires, and displayed that information. For
example, in an F250, the ABS module received a speed signal from a
sensor on the rear differential and repeated it onto a wire going to the
cluster. The cluster took that speed signal (a series of pulses,
essentially), determined the speed and distance traveled, and moved the
speedometer needle and odometer. I'm sure an Explorer worked the same way.
The GEM would have wires going to the cluster to turn on 4x4 and Low
lights, but right off hand those are the only things I can think of.
I don't think the GEM had any hand in the radio. I'm pretty sure the
radio's were standalone units, with there own direct wiring for rear
seat controls, etc.
Yes. The headlight switch had an Off, Park and Headlight position that
directly powered the right relays to turn on the right lights. The
switch also had an autolamp position that handed control over to the
GEM. The GEM had a sun load sensor and relays that could turn on the
head and park lights. It could also flash the park lights when remotes
locked the doors or an alarm was triggered. All of those may or may not
have been part of a particular model, or package. It would depend on the
This I'm not entirely sure about. I know in earlier years there were
feature specific GEM's. Those, once you identified the right one, were
pretty easy to put in. Later years I think things got more programmable
and you would need to be able to program the features of the GEM for the
options of a particular vehicle. I'm not familiar enough with models
older than about 2004 to know for sure.
I know by 2004, at least in the trucks, the GEM had been eliminated
altogether and was replaced by things like the Vehicle Security Module,
the 4WD Control Module and others.
I'm sure they did. My Dad's '98 had PATS (Passive Anti-Theft System),
which was an RFID chip in the key. And it had both Remote Keyless Entry
and a keypad on the door. Keyless entry and the keypad were controlled
by the GEM. The GEM learned the key-fob codes and responded to them by
controlling relays that activated the door locks, flashed the lights and
beeped the horn.
But I think PATS was more complicated as it was either part of the
engine computer itself, or a separate module that spoke directly to the
engine computer. I know that if the correct PATS key wasn't in the
ignition, the engine computer simply wouldn't let the engine start. And
as the engine computer controlled both fuel delivery and ignition, it
was pretty effective.
As an aside, it also just occurs to me that the GEM probably controlled
the interior lights, exterior courtesy lights and accessory power as
well. Interior lights came on when a door was unlocked with a key fob,
and stayed on for a set time after the door was locked. On higher level
packages there were exterior courtesy lights that lit the running boards
and the ground below the door that came on and went off in a similar
fashion. And by 2001 the Accessory Delay feature was pretty common,
where the radio, power windows and other accessories stayed on after the
key was turned off, until a set amount of time had passed or a door was
opened. All of those features would have been controlled by the GEM.
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