High Intensity Discharge Ballast - Operation

OPERATION

The electronic ballast module operates on battery current and ground received directly from the Body Control Module (BCM) (also known as the Common Body Controller/CBC). Each module controls operation of the High Intensity Discharge (HID) igniter and lighting element for the front lamp unit on which it is installed. The BCM monitors a hard wired input from the headlamp switch to determine the proper control outputs to the electronic ballast module, which then provides a controlled voltage to operate the HID lamp igniter as appropriate.

The BCM also monitors electronic message inputs received from the Steering Control Module (SCM) over the Controller Area Network (CAN) Interior High Speed (IHS) data bus based upon multi-function switch inputs and, if the vehicle is so equipped, from the SmartBeam(R) (also known as the Automatic High Beam Module/AHBM) and the Light/Rain Sensor Module (LRSM) (also known as the Rain Sensor Module/RSM or Rain/Light Sensor Module/RLSM) to determine the proper lighting outputs to provide to the ballast module.

When a proper 12 volt Direct Current (DC) control output is received from the BCM, the HID electronic ballast module activates the HID igniter integral to the lighting element through a high-tension cable to provide a high voltage (up to about 800 volts Alternating Current/AC) surge. The igniter further steps up this AC voltage to up to about 25,000 volts, which creates a light arc between the lighting element electrodes. Once the igniter and electronic ballast module detect a suitably stable light arc, they switch over to a power-limiting mode to sustain the light arc, which requires only about 85 volts to sustain proper lighting element output.

The hard wired electronic ballast module circuits may be diagnosed using conventional diagnostic tools and procedures. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the electronic ballast module or the electronic controls and communication that provide some features of the HID lamp system. Proper diagnosis of the electronic ballast module, the BCM, the SCM, the SmartBeam(R), the LRSM, the CAN data bus and the electronic communication related to electronic ballast module operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.