Headlamp: Description and Operation

HEADLAMPS
The headlamps consist of 2 interchangeable single filament bulbs or 2 high intensity discharge (HID) arc tubes and ballast on each side of the vehicle which provide high and low beams. The lower bulb in the headlamp is the high beam and the upper bulb is the low beam.

The headlamps may be turned ON in 3 different ways:
- When the headlamp switch is placed in the ON position, for normal operation
- When the headlamp switch is placed in the AUTO position, for automatic lamp control (ALC)
- When the headlamp switch is placed in the AUTO position, with the windshield wipers ON in daylight conditions, after a 6 second delay

With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the turn signal/multifunction switch at G200. In response to this input, the instrument panel module (IPM) provides ground to either the headlamp low beam relay control circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay coil has ground. The IPM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery positive voltage to both relay switch circuits. When the low beam relay coil is energized, current flows through the LT LOW BEAM and the RT LOW BEAM fuses to the low beam headlamps. The low beam headlamps are grounded at G104. When the headlamp high beam relay coil is energized, current flows through the LT HI BEAM and the RT HI BEAM fuses to the high beam headlamps. The high beam headlamps are also grounded at G104. When the headlamp dimmer switch lever is pulled toward the driver, the flash to pass (FTP) switch closes. This grounds the IPM flash to pass switch signal. In response to this input, the IPM energizes the high beam relay. Both high beams will remain ON until the driver releases the headlamp dimmer switch handle. If the low beam headlamps were ON during FTP operation, the low beams remain ON. The headlights may be switched to high beam with the opposite movement of the headlamp dimmer switch lever. With the headlamp dimmer switch in the high beam position the IPM sends a message via GMLAN to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator. If the headlamp switch is left in the ON position, the inadvertent power control feature will turn OFF the headlights 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlights will remain ON until turned OFF or the battery runs dead.

During automatic lamp control (ALC), the headlamps will be in low beam operation during low light conditions. A HEADLAMPS SUGGESTED message will appear on the driver information center (DIC) when the headlamps and park lamps are OFF due to all exterior lighting controls being inactive when dark conditions are sensed. The auto position of the headlamp switch is supplied ground at G200 and enables the auto lamp feature. When the ignition is ON, the IPM will automatically turn the headlamps ON or OFF according to the Light/Dark photocell Status.

The headlamps ON with wipers feature operates when the following conditions are true:
- The ignition is in the RUN position.
- The headlamps are currently OFF.
- The headlamp switch is in the AUTO position.
- The ambient light sensor indicates DAYTIME conditions.

When the headlamps ON with wipers feature is active the DIC will display the HEADLAMPS SUGGESTED message.

HEADLAMPS - HIGH INTENSITY DISCHARGE (HID)
The high intensity discharge (HID) system is made up of the ballast and arc tube. The headlamp ballast receives the headlamp low beam supply voltage, which would normally be used to directly supply the low beam headlamp. Each ballast has a separate ground. The HID headlamp operation consist of 3 states. The startup or strike state, run up state, and steady state. When the headlamp switch is placed in the ON position, the ballast may draw up to 20 amps. This is referred to as the strike state. The ballast will provide multiple high voltage pulses to the arc tube in order to start the bulb. The voltage provided by the ballast during the startup state ranges from -600 to +600 volts. Once an arc is established, the ballast will provide a higher then steady state voltage to the arc tube in order to keep the bulb illuminated. This is called the run up state. On a cold bulb this state could last as long as 41 seconds. On a hot bulb, the run up state may last as long as 15 seconds. Steady state operation begins when the bulb reaches the 35 watt power level. The ballast provides the bulb with a minimum of 55 volts during steady state operation.

For proper operation of the HID system, ensure the battery and the harness are capable of supplying up to 20 amps of current per ballast, with less than 2 volts of system loss or voltage drop. Each ballast requires up to 20 amps in order to ensure normal startup and run up of the lamp.

The range of white light that is acceptable is broad when compared to halogens. Therefore, some variation in headlight coloring between the right and left headlamp will be normal. Replace the arc tube only if the arc tube is determined to be at the bulb failure stage.

HEADLAMPS - INTELLIBEAM
The intellibeam system operates the high beam headlamps ON and OFF automatically when certain conditions are met and the system is activated. The system consists of a digital light sensor that is located in a separate module that is mounted to the back of the inside rearview mirror. The digital sensor detects light, not vehicle movement. The sensor analyzes light color, intensity, and movement. The intellibeam system will turn OFF the high beam headlamps when other vehicles headlamps or taillights are detected by the digital sensor. Intellibeam can be deactivated when the headlamp dimmer switch is moved from the neutral position to the high beam or flash to pass (FTP) positions. When the headlamp dimmer switch is returned to the neutral position, intellibeam will be enabled.

Intellibeam modulates the high beam headlamps by gradually fading the high beam headlamps ON or OFF. Intellibeam is designed to ignore non-vehicular light sources. However, the system may dim the high beams if it detects lighting or lighting reflections similar in color and intensity to vehicle lighting. When this occurs, intellibeam will dim the high beams until the light or reflection source is no longer detected.

IMPORTANT: Intellibeam may not operate properly if any of the following conditions exist:

- The other vehicles lamps are undetectable due to dirt, snow, road spray, smoke, fog, or any other airborne conditions.
- The vehicle windshield is covered with ice, dirt, snow, haze, or the intellibeam digital light sensor is obstructed.
- The vehicle ride height is such that the front of the vehicle is pointed upward causing the intellibeam light sensor to be aimed high.
- The vehicle is being driven on winding or hilly road conditions which would make any on coming vehicle headlamps undetectable by the intellibeam.

Cleaning the intellibeam digital light sensor should be done periodically to ensure system performance. To clean the sensor, use glass cleaner and a soft cloth. Apply the glass cleaner to a soft cloth and gently wipe the light sensor lens. Do not apply the glass cleaner directly to the light sensor lens.

IMPORTANT: The intellibeam system operates when the following conditions are met:

- The headlamp switch is in the AUTO position.
- The headlamp dimmer switch must be in the neutral position.
- Intellibeam has been turned ON by pushing the AUTO button located on the face of the rearview mirror.
- Outside conditions must be dark.
- Intellibeam will only function when the vehicle is in DRIVE and moving.

Speed Thresholds:
- Accelerating: As the vehicle is accelerating, intellibeam will gradually apply the high beams when vehicle speed reaches 32 km/h (20 mph) or greater. Full high beam intensity will not occur until the vehicle has achieved a speed of 40 km/h (25 mph) or greater.
- Decelerating: As the vehicle is decelerating, intellibeam will fade the high beams down until they are completely OFF at or below 24 km/h (15 mph).

IMPORTANT: The high beam indicator located on the instrument panel cluster (IPC) will turn ON as soon as the high beams are energized even thought full intensity has not been achieved. The high beam indicator will not turn OFF until the high beams have faded completely OFF.

IMPORTANT:
- Enabling and disabling the intellibeam system can be achieved by performing the following:
- Intellibeam is automatically disabled each time the vehicle is started. To disable intellibeam after the system has been enabled, press the intellibeam AUTO button on the rearview mirror for 3 seconds and releasing it after the green LED intellibeam status indicator on the left side of the rearview mirror flashes 2 times. When this is done, the intellibeam system will not be active until the system is manually turned ON.
- Intellibeam is enabled by pressing and releasing the intellibeam AUTO button located on the rearview mirror after the vehicle has been started. The green LED intellibeam status indicator located on the left side of the rearview mirror will flash 1 time to indicate the system has been turned ON.