Principles of Operation

NOTE: The Front Electronic Module (FEM), the Rear Electronic Module (REM) and the Instrument Cluster Module (ICM) must be reconfigured before installing a new module. Refer to Module Communications Network (Information Bus).

The vehicle electronic functions are divided into zones. The FEM controls the front portion of the vehicle and the REM controls the rear portion of the vehicle. These systems rely on the Standard Corporate Protocol (SCP) communication network in order to transmit and receive signals. As a technician it is very important to understand:
^ where the input (command) originates from.
^ all information (messages) necessary in order for a feature to operate.
^ which module(s) receive(s) the input or command message.
^ does the module which received the input (message) control the output of the feature, or does it output a message over the SCP communication network to another module.
^ which module controls the output of the feature.

Exterior Lighting
The exterior lighting outputs are zone controlled by the FEM and REM. The front exterior lights are controlled by the FEM and the rear exterior lights are controlled by the REM. An additional function of the lighting system is a lamp outage function which indicates to the driver if certain exterior bulbs are not functioning. With a bulb inoperative, the FEM or REM will send a message to the instrument cluster and message center (if equipped with the message center), which will indicate to the driver that the lamp is inoperative with a lamp out indicator (with the message center a message will be displayed). To provide complete input and output functionality, each exterior lamp feature will be described individually. All exterior lighting is powered by the Switched System Power (SSP) feature (refer to Switched System Power). A failure of all or any of the SSP features will cause inoperative exterior lighting. When diagnosing exterior lighting, it is essential to determine if all related symptoms and Diagnostic Trouble Codes (DTCs) are controlled by the SSP feature.

Headlamps
The headlamps are controlled by the FEM and instrument cluster module. The headlamp and multifunction switches are hardwired to the instrument cluster. When the headlamp switch is in any position, the instrument cluster module will send a command to the FEM through the SCP communication network. The FEM will process this information and output the appropriate command to the headlamps, which are hardwired to the FEM. This is the same for the low and high beams and flash-to-pass position. Daytime Running Lamps (DRL) is an additional feature which the FEM may be configured to include. Left and right low, as well as high beams will provide a lamp outage indication. Fault management of the headlamps will provide some headlamp functionality. In the event of all multifunction switch, all headlamp switch or ignition switch invalid or missing data failures, the low beams will be illuminated. There is also a headlamp battery saver feature. This feature turns off the headlamps in ten minutes after the ignition is turned off.

The vehicle electronic functions are divided into zones. The FEM controls the front portion of the vehicle and the REM controls the rear portion of the vehicle. These systems rely heavily on the SCP communication network in order to transmit and receive signals. As a technician it is very important to understand:
^ where the input (command) originates from.
^ all information (messages) necessary in order for a feature to operate.
^ which module(s) receive(s) the input or command message.
^ does the module which received the input (message) control the output of the feature, or does it output a message over the SCP communication network to another module.
^ which module controls the output of the feature.

Switched System Power (SSP)
The SSP is invoked by both the FEM and REM. This function removes power from relays that provide power to the exterior lamps, interior lamps, and power door locks. This is only accomplished when both the FEM and the REM are in sleep mode. The sleep function of the FEM and REM places the modules in sleep mode when the ignition switch is in the OFF position, and no wake up (input) signals occur for 30 minutes. The module will not sleep if the parking lamps or the hazard lamps are active. The following relays are controlled by the SSP function: SSP1, SSP2, SSP3, and SSP4. When either the FEM or REM are not in sleep mode, all SSP relays will be energized. When energized, each relay will supply power to multiple features/functions.