Courtesy Lamp: Description and Operation

PRINCIPLES OF OPERATION

NOTE: A new front electronic module (FEM) or rear electronic module (REM) must be reconfigured before installing. REFER to Module Communications Network (Information Bus).

The 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.
- 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 rear electronics module (REM), driver door module (DDM), and instrument cluster. The FEM interprets the inputs and, in turn, commands the correct output. The FEM also receives inputs which come directly from components hardwired to the module, such as the front door ajar switches.

Interior Lighting
The FEM controls the outputs to all interior lighting. The lamps are illuminated if any door is ajar. The front door switches are hardwired to the FEM. When either of the two doors is opened, the FEM commands the interior lamps on by supplying the ground circuit. The rear door ajar switches are hardwired to the REM. When any of these doors are ajar, the REM sends a command through the SCP network to the FEM. The FEM then commands the appropriate interior lamps on.

Fault management of the interior lamps provides 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. 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 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 the 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. Refer to the SSP Relay Index for diagnosis and testing of SSP-related issues. SSP Relay Index