Courtesy Lamp: Description and Operation

NOTE: The Front Electronic Module (FEM), Rear Electronic Module (REM), and Driver Door Module (DDM) must all be reconfigured before installing a new module.

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 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.
^ whether the 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.

FEM Operation
This system is unique in that many of the inputs the FEM receives are delivered via the SCP communication network. These input messages come from other modules connected to the network, such as the REM, DDM, and instrument cluster. The FEM will interpret the inputs and, in turn, command the correct out put. The FEM also receives inputs which come directly from components which are hardwired to the module, such as the passenger door ajar switch.

Interior Lighting
The FEM controls the outputs to all interior lighting. The interior lamps include: courtesy lamps, dome lamps, and map lamps. The lamps will be illuminated if the driver or front passenger door is ajar. The switches are hardwired to the FEM. When any of the two doors are opened, the FEM will command the interior lamps through the SCP network to the FEM. The right and left rear ajar switches are hardwired to the REM. When any of these doors are ajar, the REM will send a command through the SCP network, to the FEM. The FEM will command the appropriate interior lamps on.

The FEM also handles the grounds for the glove box and the visor lamps. Fault management of the interior lamps will provide limited functionality in the event of certain dome or lighting mode inputs, vehicle speed or ignition switch failures. All interior lighting is powered by the Switched System Power (SSP) feature (refer to Switched System Power). A failure of any or all of the SSP feature(s) could cause inoperative interior lighting. When diagnosing the interior lighting, it is essential to determine if all relative symptoms and Diagnostic Trouble Codes (DTCs) are controlled by the SSP 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 (inputs) 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. Each relay, when energized, will supply power to multiple features/functions.