Headlamp: Description and Operation

The instrument cluster monitors both the multiplexed headlamp and multifunction switches. The instrument cluster transmits a J1850 bus message to the front control module (FCM) to activate the headlamps. The headlamp system will default to headlamps ON position when ignition switch is ON and when an open or short circuit failure occurs on the headlamp switch input to the instrument cluster. The system will return to normal operation when the open or short is repaired. A fault will be reported by the Instrument Cluster when a failure occurs on the dimmer or headlamp switch input.

If the exterior lamps are ON, and the headlamp switch is in any position other than OFF, with the ignition switch OFF (LOCK) after 5 minutes, the Instrument Cluster transmits a message via J1850 informing the the FCM. The FCM will then turn off the headlamps, park lamps and fog lamps. This feature (load shed) prevents the vehicle battery from being discharged when the vehicle lights have been left ON.