What does the "GEM" module do? (2001 Ford Explorer)

Yes

The GEM did body related functions like keyless entry, electric windows, auto lamps and locks, stuff like that. One some models it did Electronic Shift on the Fly 4WD functions.

No, other than the aforementioned 4WD on some models.

It might do auto lamps. It would depend on the model, year and if that was an option. Auto lamps might have been done by the HEC (Hybrid Electronics Cluster) too. I'm not entirely sure at the moment.

Not in 2001, no. At least not that I've ever heard of.

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 options.

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.

Gem module 95 ford explorer eb 4wd It all of sudden door ajar and interior lights staying on.occasionally if v ehicle cold light will go off but not after that.also the instrument panel will flash 4wd, 4wd low can amyone give me some info please and ty!? ??

As a trouble shooting aid, Duct Tape a small square of cardboard to the area on the door where the switch mounted in the door frame contacts the switch actuator. IF there is no door frame mounted switch then the switch is in the door handle mechanism and it may need a squirt of lube.