General Module: Description and Operation

The generic electronic module (GEM) controls several vehicle systems. The rear air suspension is controlled by the GEM. The GEM is located under the center of the instrument panel.
^ The wiring harness connects to the GEM using three separate push button release connectors.
^ The connectors are keyed so that they cannot be installed incorrectly.

The GEM operates as follows:
^ In general the GEM uses a 40.5-second averaging interval to determine when compress and vent operations are needed.
^ However, door open warning lamp switch inputs can override the 40.5-second averaging interval so compress and vent operations can begin immediately, if needed.
^ The 40.5-second averaging interval is used to keep the GEM from making unneeded corrections.
^ When a vehicle at the correct rear trim height hits a bump, the air suspension height sensor (5359) output will read low and high in addition to trim until the oscillations die out.
^ If the GEM were to correct for these "bump induced readings," system duty cycle would increase unnecessarily.
^ The 40.5-second averaging interval not only eliminates corrections due to bumps, but also eliminates unneeded corrections resulting from braking, accelerating, and turning. The GEM tabulates the air suspension height sensor readings, and does not begin a compress or vent operation until the air suspension height sensor reads low or high for 40.5 seconds consistently.
^ There are more restrictions on vent operations than there are on compress operations.
^ To eliminate the chance of catching a door on a curb as the vehicle vents down, the GEM will not allow any venting to occur when a door is open.
^ The GEM does not allow any vent operations for the first 40.5 seconds after the ignition switch has been turned to RUN without a door open and closed.
^ Even if a vehicle is extremely high in the rear DO NOT expect it to vent until the ignition switch has been turned to RUN for 40.5 seconds.

CONTROL MODULE POWER AND GROUND
The generic electronic module (GEM) has the following features:
^ B+ is provided by Circuit 785 (BK/LG), which is powered through fuse junction panel Fuse 19 (10A).
^ GEM ground is provided through Circuit 397 (BK/W).
^ The Air Suspension service switch grounds Circuit 635 (Y) in the ON position.

IGNITION SWITCH INPUT
System responds to ignition switch input as follows:
^ The GEM stays powered for one hour after the ignition switch is turned to the OFF position, in order to perform leveling corrections after occupants and luggage are removed from the vehicle. The rear air suspension service switch must be ON and all doors (including liftgate) must be closed completely.
^ When the ignition switch is turned to RUN, Circuit 137 (Y/BK) and 489 (PK/BK) are supplied B+ voltage.
^ If there is an open in Circuit 137 (Y/BK) or 489 (PK/BK) or their feed circuits, the GEM will be inoperative and diagnostics cannot be entered.

DOOR COURTESY LAMP SWITCH INPUT
System responds to door ajar switch as follows:
^ The GEM uses the door ajar switch input for two different rear air suspension system functions:
^ Preventing vents when a door is open to avoid the possibility of the vehicle lowering and the door catching on an obstruction.
^ Servicing a correction immediately, if needed.
^ The liftgate, LH front, and RH front door switches close to ground when opened, while the sliding door switch provides ground when closed and opening the door provides an Open in the circuit.
^ The GEM can sense each door (open or closed) independently.
^ If a damaged door ajar switch (door always open) exists, the GEM will interpret that a door is open and not vent unless vehicle speed is above 24 km/h (15 mph).
^ Above 24 km/h (15 mph) the GEM disregards all door signals.