High Intensity Discharge Ballast - Operation

OPERATION

The electronic ballast module operates on battery current and ground received directly from the Front Control Module (FCM). 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 FCM monitors electronic message inputs received from the Electro Mechanical Instrument Cluster (EMIC) (also known as the Cabin Compartment Node/CCN) over the Controller Area Network (CAN) data bus 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 EMIC monitors electronic switch status messages received from the Steering Control Module (SCM) over the Local Interface Network (LIN) data bus based upon left multi-function switch inputs and, depending upon vehicle equipment either a hard wired input from the sun load sensor on the top of the instrument panel or electronic message inputs from the Rain Sensor Module (RSM) (also known as the Rain/Light Sensor Module/RLSM) on the inside of the windshield below the electrochromic inside rear view mirror mounting button to determine the proper request message outputs to send to the FCM.

When a proper 12 volt Direct Current (DC) control output is received from the FCM, the HID electronic ballast module activates the HID ignition module integral to the lighting element through a high-voltage 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 FCM, the EMIC, the SCM, the RSM, the CAN data bus, the LIN 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.