Courtesy Lamp: Description and Operation

NOTE: The Front Electronic Module (FEM), Rear Electronic Module (REM), and the Remote Keyless Entry (RKE) Driver Door Module (DDM), RKE (DDM) must all be reconfigured before installing a new module. REFER to Module Communications Network (Information Bus).

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
^ 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

Interior lighting
The rear electronic module (REM) controls the outputs to all interior lighting with the exception of the stepwell/puddle lamps which are controlled by the front electronic module (FEM). The courtesy lamp mode switch is hardwired to the instrument cluster module. When the courtesy lamp mode switch is placed in the desired position, the instrument cluster will send a message to the FEM and the REM through the SCP connection network. The liftgate and left/right power sliding door ajar switches are hardwired to the REM. When any door is ajar, the module which the door ajar switch is hardwired to will send a message through the SCP link to the appropriate module in order to enable the courtesy lamps. The REM and FEM will command the appropriate lamps ON when an input is received from the courtesy lamp mode switch or from any door ajar switch. Demand lighting is controlled by the individual switch unless the switch is placed in the courtesy position. If a demand lamp switch is in the courtesy position, the switch will function when the courtesy lamps are commanded ON. 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, for additional information, refer to Switched System Power (SSP). A failure of all or any of the SSP features will cause inoperative interior lighting. When diagnosing interior lighting it is essential to determine if all related symptoms and DTCs are controlled by the SSP feature. The illuminated exit feature can be enabled or disabled using the scan tool, for additional information, refer to Module Communications Network (Information Bus).

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. For additional information, refer to the SSP Index for diagnosis and testing of SSP related issues.