Turn Signals: Description and Operation

NOTE: The Front Electronic Module (FEM), the Rear Electronic Module (REM), and the instrument cluster must all 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. 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. The headlamp and multifunction switches are hardwired to the instrument cluster. When the lamps are commanded ON or OFF, the instrument cluster sends the command for the exterior lamps through the standard corporate protocol (SCP) network to the FEM and REM. 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 DTCs are controlled by the SSP feature.

Turn Signal Lighting
The turn signals are divided into two areas. The front and the rear. The left and right front turn lamp outputs are controlled by the FEM and the left and right rear turn lamps are controlled by the REM. The multifunction switch is hardwired to the instrument cluster. When the switch is in the left or right turn position, the instrument cluster sends a command via the SCP network to the FEM and the REM. The FEM will in turn process this information and output the appropriate command to the front turn lamps. The REM will in turn process this information and output the appropriate command to the rear hazard lamps, which are the turn signal lamps. All lamps provide lamp outage indication.

Hazard Lighting
The hazard lamp switch is hardwired to the instrument cluster. When the switch is in the hazard position, the instrument cluster sends a command via the SCP network to the FEM and REM. The FEM will in turn process this information and output the appropriate command to the front hazard lamps. which are the turn signal lamps. The REM will in turn process this information and output the appropriate command to the rear hazard lamps, which are the turn signal lamps.

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. If a state change does occur, the 30 minute timer will reset and begin again. 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. When diagnosing multiple symptoms and/or DTCs it is essential to determine if all are related to a single SSP or multiple SSP relay powered functions.