Description & Operation

Autolamp system provides light-sensitive automatic on-off control of exterior lights normally controlled by regular headlight switch. Autolamp is activated by turning headlight switch to autolamp position. Autolamp system consists of the autolamp sensor, exterior lighting system, Front Electronic Module (FEM), Rear Electronic Module (REM) and Instrument Cluster Module (ICM). Autolamp system uses the Standard Corporate Protocol (SCP) communication network to transmit and receive signals. It is very important to understand where command messages originate from, which modules can send command messages, which modules receive command messages and what control module requested command message operations. Autolamp system is powered by the Switched System Power (SSP) feature, which can disable autolamp system operation for energy conservation. The following are descriptions of autolamp system and related system features:

1. Autolamps
   
   Autolamp system is powered by the SSP feature. Autolamps are controlled by headlight switch, autolamp sensor, ICM and FEM. When headlight switch is in autolamp position, ICM sends an ON/OFF command message to FEM. Depending on signal from autolamp sensor FEM will process this information and output appropriate command message to headlights. Autolamps will remain on for approximately 20 seconds after ignition switch is turned from RUN position to ACC or OFF position. Autolamps function and Daytime Running Lights (DRL) function may be configured by FEM.
2. Exterior Lighting
   
   The front exterior lights are controlled by the FEM and the rear exterior lights are controlled by the REM. An additional function of lighting system is a light outage function which provides indication to driver if certain bulbs are not functioning. When a bulb is open or burnt out, FEM or REM will send a message to ICM and message center bulb out indicator (if equipped). All exterior lights are powered by SSP. A failure of any or all SSP features could cause exterior lighting to become inoperative. When diagnosing exterior lighting, it is essential to determine if related symptoms or Diagnostic Trouble Codes (DTC) are controlled by SSP feature, and verify SSP feature for exterior lighting is enabled.
3. Foglight
   
   Foglights are controlled by headlight switch. When foglights are activated, headlight switch sends voltage to ICM, which sends a signal to FEM which activates foglights.
4. Headlights
   
   Headlights are controlled by FEM and ICM, and operated from headlight and multifunction switches which are hard wired to instrument cluster. When headlight switch is in any position, ICM will send a command message to FEM through SCP communication network. FEM processes this information and sends appropriate command to headlights. High beams and flash-to-pass functions are also controlled by multifunction switch. Headlight low beam and high beam circuits are monitored and should provide headlight outage indication to message center (if equipped). In case of fault in multifunction switch, headlight switch or ignition switch invalid/missing data failures should occur, headlight low beams will remain illuminated and all other headlight settings will be disabled.
5. Parking, Rear Or License Plate Lights
   
   Left and right front parking lights are controlled by FEM. Left and right rear parking and license plate light are controlled by REM. When headlight switch is on or parking lights are on, headlight switch sends a signal to ICM. ICM then sends a command message through SCP to FEM or REM, which signals appropriate lights. Only left and right rear taillights will provide light outage indication. In case of certain headlight switch, ignition switch or REM failures, rear parking light operation should be provided. Parking lights are also part of DRL feature.
6. Reverse Lights
   
   Reverse lights are controlled by REM and Powertrain Control Module (PCM). When transmission is placed in Reverse, PCM sends a message through SCP to REM, which processes this information and sends a command message for reverse light illumination.
7. Brakelights
   
   Brakelights are controlled by REM and Brake Pedal Position (BPP) switch. BPP switch inputs information to REM when brake pedal is depressed. REM then processes information and output to left, right and high-mounted brakelights. Only left and right brakelights provide light outage indication.
8. Turn Signal, Cornering & Hazard Lights
   
   FEM controls front turn signals, hazard lights and cornering lights. REM controls rear turn signals and hazard lights. When multifunction switch is in either turn indicator position or hazard switch is on signals are sent to ICM. ICM then sends a command message over SCP network to either FEM or REM, which applies power to appropriate lights. When a turn signal is commanded by ICM, FEM also commands appropriate cornering light to illuminate. All turn signal lights will provide outage indication.
9. Interior Lighting
   
   FEM controls outputs to courtesy lights, dome light and map lights. Driver and passenger door ajar switches are hard wired to FEM and will illuminate appropriate lights when either door is ajar. Rear door ajar switches are hardwired to REM. When either rear door is opened, REM will send a command over SCP network to FEM. FEM will command appropriate interior lights on.
10. Switched System Power
    
    SSP is invoked by FEM and REM, and removes power from appropriate SSP relay. SSP relays can enable or disable power supply for autolamp/headlights, exterior lights, interior light operation, in addition to other vehicle electrical systems. FEM and REM are in sleep mode with ignition switch in LOCK position and no wake up (inputs) occur for about 30 minutes. Sleep mode is not entered if parking or hazard lights are active. SSP relays (SSP1, SSP2, SSP3 and SSP4) supply power to multiple features/functions. See SWITCHED SYSTEM POWER RELAY INDEX  table.