High Intensity Discharge (HID) Low Beam Headlamps

WARNING: This page is about a different car, the 2007 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.

High intensity discharge (HID) headlamps do not have filaments like the traditional headlamp bulbs. Instead a ballast and an arc tube is used.

When the headlamp switch is placed in the HEAD position, ground from G304 is applied through the headlamps ON signal circuit to the body control module (BCM). In response to this signal, the BCM applies ground to the headlamp low beam relay control circuit energizing the LO BEAM PCB Relay. With the relay energized, battery voltage is applied through the switched side of the relay, the LT and RT LO BEAM fuses, and the supply voltage circuits to a ballast located in each headlamp assembly. The ballast is used to increase the input voltage into a higher voltage in order to create an arc between the electrodes in the arc tube illuminating the headlamp. Ground for the left and right headlamps is provided at G104.