Principles of Operation

NOTE: The Front Electronic Module (FEM), the Rear Electronic Module (REM), and the Instrument Cluster Module 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 heavily 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.

Extenor 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 SSP feature (refer to [SSP]). 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 DTCs are controlled by the SSP feature.

The vehicle's 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.

Fog Lamps
The fog lamps are controlled by the headlamp switch. The switch toggles the fog lamps between on and off. When activated, the switch sends voltage to the instrument cluster. The instrument cluster sends a signal to the FEM which activates the fog lamp.

The vehicles 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.
^ whether module which received the input (message) controls the output of the feature, or whether it outputs 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. For additional information, go to the SSP Index Component Tests and General Diagnostics
for diagnosis and testing of SSP related issues. Refer to Headlamps. Headlamp