Headlamp Mode
WARNING: This page is about a different car, the 2005 GMC Sierra and 2005 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The generator battery control module will enter the Headlamp Mode when the headlamps, low or high beams, are turned ON. The voltage will ramp up or down to 14.5 volts at a rate of 10 mV/second. The module will exit this mode once the headlamps are turned OFF and enter Charge Mode, Fuel Economy Mode, or Voltage Reduction Mode.