Automatic Headlamps

The optional automatic headlamp system includes the headlamp switch, the Body Control Module (BCM), the Heating, Ventilation and Air Conditioning (HVAC) module and the sun load sensor on the top of the instrument panel.

The sun load sensor provides an ambient light level input to the HVAC module whenever the ignition switch is in the ON position. The HVAC module responds to this input by sending the appropriate electronic light level  messages to the BCM over the Controller Area Network (CAN) data bus. When the AUTO  (Automatic) position is selected with the headlamp switch, the BCM receives a hard wired multiplex input from the headlamp switch. The BCM also receives electronic messages over the CAN data bus from the Powertrain Control Module (PCM) indicating the engine is running.

The BCM responds to these input conditions by automatically controlling a Pulse-Width Modulated (PWM) voltage output to the selected headlamp bulb filaments through the right and left low or high beam driver circuits to illuminate the headlamps. The BCM also remembers which beams (low or high) were selected when the headlamps were last turned OFF, and energizes those beams and lamps again the next time it turns the headlamps ON.