Low Beams - High Intensity Discharge (HID)

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2008 GMC Yukon XL, 2008 GMC Yukon, 2008 Chevrolet Tahoe, 2008 Chevrolet Suburban, and 2008 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

Normal operation of the HID system starts at the ballast. The headlamp ballast input connector receives battery positive voltage from fuses in the underhood fuse block. When the low beam headlamps are requested the low beam relay supplies voltage to the ballast on the right headlamp low beam supply voltage circuit and the left headlamp low beam supply voltage circuit, which in turn begins the low beam operation as follows. As soon as the input power is applied, the ballast draws 20 amps from the battery for 5-10 seconds, depending on the input voltage level. The ballast is then able to charge the 2 outputs leading to the start to -360 volts and +800 volts. Negative 360 volts and +800 volts are the voltages needed by the starter to strike or start the lamp. HID headlamps do not have filaments like traditional bulbs, instead, the starter uses a high voltage transformer to convert the +800 volts input power into 25,000 volts. The increased voltage is used in order to create an arc between the electrodes in the bulb. The creation of this arc begins the start up process.