Service Information

Having a firm grasp on the design and normal operation of the electrical system will aid in properly diagnosing and repairing any faults with electrical components and/or circuitry.

When the vehicle is at rest (ignition key turned off and removed), some amounts of battery current drain will be present since many of the modules and electronic components in the vehicle require this to sustain memory and system monitoring. The Powertrain Control Module (PCM), Anti-lock Brake Module (ABS), Electronic Automatic Temperature Control Module (EATC), Front Electronics Module (FEM), Rear Electronics Module (REM), Driver Door Module (DDM), Instrument Cluster Module (1CM), Roof Opening Panel Module, Heated Seat Module, Driver Seat Module, Cell Phone Module and Vehicle Emergency Message System Module all have power supplied at all times for this purpose. Many of these modules monitor activity and communicate with each other through the Standard Corporate Protocol (SCP) Link.

When the ignition key is first shut off and removed, the vehicle is exited and the doors are closed, the electrical system goes into "stand-by" mode, where the REM and the FEM keep the System Switched Power (SSP) relays activated. After a minimum of 45 minutes, the REM and FEM will power down to prevent battery discharge. Power down mode occurs when the REM and FEM "time out" and release the ground on all four (4) of the SSP relays. The SSP relays are wired in a fashion in which they are either all on or all off. In other words, the SSP relays cannot be operated independent of each other. If power down does not occur, because of a system fault or errant SCP Link activity, the REM and FEM will remain energized along with the SSP relays and the other electrical devices that they provide power. The REM and FEM provide power and ground to devices such as exterior/interior lighting and many of the body modules in the vehicle. The Wiring Diagrams Manual may be referenced for additional information on the SSP relays, the REM and FEM, in Sections 13 and 59.

Once the REM and FEM enter power down mode they will not energize the SSP relays until they are commanded to "wake up" by one (1) or more of the following commands:

^ Key Fob Activity (Any Command)

^ Door Ajar (Any Door)

^ Luggage Compartment Ajar Switch

^ Drivers Power Seat Switch

^ Power Tilt/Telescopic Steering Column

^ Headlamps/Park Lamps On

^ Key In Ignition

^ Key On Ignition

^ Anti-Theft Hood Switch

^ Brake Pedal Position Switch Memory Seat Switch