The exterior lighting consist of the following lamps:

Battery positive voltage is applied at all times to the coil and switched side of the low beam relay. Ground is applied at all times from G201 to the multifunction headlamp switch. When the multifunction headlamp switch is placed in the HEAD position, ground is then applied from the multifunction headlamp switch through the headlamps ON signal circuit to the body control module (BCM). The BCM then applies a ground to the headlamp low beam relay control circuit. This energizes the low beam relay, closing the switched side and applies battery positive voltage to the LEFT and RIGHT LOW BEAM fuses. Battery positive voltage is then applied from the fuses, through the low beam voltage supply circuits to the ballast in the headlamp assembly. When battery positive voltage is applied to the headlamp ballast through the low beam voltage supply circuits, the ballast will then charge the starter to start the lamp. High intensity discharge (HID) headlamps do not have filaments like traditional bulbs, instead the starter uses a high voltage transformer to convert the input voltage into a higher voltage. This increased voltage is used in order to create an arc between the electrodes in the bulb.

The ground for the headlamps is supplied from G101 for the left and G102 for the right.

High Intensity Discharge (HID) High Beam Headlamps

Battery positive voltage is applied at all times to the coil and switched side of the high beam relay. Battery positive voltage is also applied at all times through the coil side of the low beam relay to the low beam relay control circuit, to the multifunction headlamp switch. When the multifunction headlamp switch is placed in the high beam position, battery positive voltage is applied through the high beam headlamp dimmer switch signal circuit to the BCM. The BCM then applies a ground to the high beam relay control circuit. This energizes the high beam relay, closing the switched side of the high beam relay, applying battery positive voltage to the Left and Right High Beam Fuses. Battery positive voltage is then applied from the High Beam Fuses through the high beam solenoid switched voltage supply circuit to the high beam solenoid assembly inside of the headlamp. This causes the solenoid to retract a plate partially covering the low beam headlamps and allowing the lamps to illuminate at full brightness.

Run Up Of The Lamp

Each ballast requires higher amperage in order to ensure normal startup and run up of the lamp. Run up is the term used to describe the extra power level given to the bulb. The input current during the steady state operation is lower that the start up amperage. After the lamp receives the strike from the starter and the arc is established, the ballast uses its operating voltage in order to provide the run up power needed in order to keep the lamp ON. The lamp rapidly increases in intensity from a dim glow to a very high-intensity, bright light called a steady state. Within a few seconds of the arc being established in the bulb, the majority of steady state is complete. One hundred percent of the steady state is completed shortly there after. A high watt power level is necessary in order to bring the lamp to a steady state in such a short period of time. The high watt power level allows the lamp to meet the SAE light vs. time specification.

When To Change The HID Bulb

Bulb failure, end of life occurs when the bulb gets old and becomes unstable. The bulb may begin shutting itself OFF sporadically and unpredictably at first, perhaps only once during a 24-hour period. When the bulb begins shutting itself off occasionally, the ballast will automatically turn the bulb back on again within 0.5 second. The ballast will re-strike the bulb so quickly that the bulb may not appear to have shut OFF. As the bulb ages, the bulb may begin to shut-off more frequently, eventually over 30 times per minute. When the bulb begins to shut-off more frequently, the ballast receives excessive, repetitive current input. Repetitive and excessive restarts or re-strikes, without time for the ballast to cool down, will permanently damage the ballast. As a safeguard, when repetitive re-strikes are detected, the ballast will not attempt to re-strike the lamp. The ballast then shuts down and the bulb goes out.

The following symptoms are the noticeable signs of bulb failure:

Input power to the ballast must be terminated in order to reset the ballast's fault circuitry. In order to terminate the input power to the ballast, turn the lights off and back on again. Turning the lights off and back on again resets all of the fault circuitry within the ballast until the next occurrence of excessive, repetitive bulb re-strikes. When excessive, repetitive bulb re-strikes occur, replace the starter/arc tube assembly. The ballast will begin the start-up process when the starter/arc tube assembly is replaced. Repeatedly resetting the input power can overheat the internal components and cause permanent damage to the ballast. Allow a few minutes of cool-down time in between reset attempts.

Bulb failures are often sporadic at first, and difficult to repeat. Technicians can identify bulb failure by observing if the problem gets progressively worse over the next 100 hours of operation.

Light Color

White light has a different color rating than regular headlamps. 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. One HID at the end of the normal range may appear considerably different in color from one at the other end of the range. Difference in color is normal. Replace the arc tube only if the arc tube is determined to be at the bulb failure stage.

The AFL consist of the following components:

Battery positive voltage is applied to the headlamp control module at all times and when the ignition switch is in the RUN and CRANK positions. The headlamp control module has an operational voltage range of about 10.5-16 volts and is only fully functional when the ignition switch is in the RUN position. The voltage input from the ignition switch wakes the headlamp control module microprocessor. The headlamp control module receives serial data messages via GMLAN from the engine control module (ECM), transmission control module (TCM), electronic brake control module (EBCM), and body control module (BCM) with regards to power mode, speed, steering angle, transmission gear selection, and headlamp switch status. The headlamp control module calculates the headlamp angle and sends commands to the left and right headlamp actuators. The headlamp actuators drive the headlamps to the position commanded by the headlamp control module. The headlamp control module monitors the headlamp actuator motor control circuits for proper circuit continuity and for shorts to ground or voltage. If a malfunction is detected, a DTC will be stored in memory and the driver will be notified with a message displayed over the driver information center (DIC) located on the instrument panel cluster (IPC).

The headlamp control module controls the left headlamp movement by 15 degrees to the left and 5 degrees to the right, and the right headlamp movement by 5 degrees to the left and 15 degrees to the right. The direction the headlamps move is controlled by the steering wheel angle and is limited by steering angles of approximately +/- 90 degrees. The AFL will not operate with the transmission in reverse or at vehicle speeds less than 2 mph. Movement of the headlamps is restricted at low vehicle speeds and full movement of the lamps is not allowed until vehicle speed is greater than approximately 30 mph. The following conditions must be met before the AFL will operate:

Place the multifunction headlamp switch in the OFF position for automatic lamp control. During automatic lamp control the headlamps will be off during daylight conditions but will turn on when the ambient light sensor detects low light level. The ambient light sensor is a light sensitive transistor that varies the voltage signal to the HVAC control assembly. The HVAC control assembly then sends a signal to the body control module (BCM) through the class 2 message circuit commanding the BCM to apply a ground to the headlamp low beam relay control circuit. This energizes the low beam relay, closing the switched side and applies battery positive voltage to the LEFT and RIGHT LOW BEAM fuses. Battery positive voltage is then applied from the fuses, through the low beam voltage supply circuits to the ballast in the headlamp assembly. When battery positive voltage is applied to the headlamp ballast through the low beam voltage supply circuits, the ballast will then charge the starter to start the lamp. High intensity discharge (HID) headlamps do not have filaments like traditional bulbs, instead the starter uses a high voltage transformer to convert the input voltage into a higher voltage. This increased voltage is used in order to create an arc between the electrodes in the bulb. The ground for the headlamps is supplied from G101 for the left and G102 for the right.

When the low beam headlamps are ON and the multifunction headlamp switch is momentarily placed in the flash to pass (FTP) position, ground is applied from G201 to the multifunction headlamp switch. The multifunction headlamp switch applies a ground to the BCM through the FTP switch circuit. The BCM then applies a ground to the high beam relay control circuit. This energizes the high beam relay, closing the switched side of the high beam relay, applying battery positive voltage to the Left and Right High Beam Fuses. Battery positive voltage is then applied from the High Beam Fuses through the high beam solenoid switched voltage supply circuit to the high beam solenoid assembly inside of the headlamp. This causes the solenoid to retract a plate partially covering the low beam headlamps and allowing the lamps to illuminate at full brightness momentarily.

The ambient light sensor is a light sensitive transistor that varies the voltage signal to the HVAC control assembly. The HVAC control assembly then sends a signal to the body control module (BCM) through the class 2 message circuit commanding the BCM to turn the front turn lamps on steady (non-flashing). Any function or condition that turns ON the headlamps will cancel the daylight running lamps (DRL) operation. With the headlamp switch in the OFF position, the turn signal lamps will either be turned ON or OFF after a 30-second delay, depending on whether daylight or low light conditions are sensed by the ambient light sensor. The DRL operates when the ignition switch is in the RUN position, the parking brake is not set and the transmission is not in the PARK position. When these conditions have been met, and the ambient light sensor indicates daytime conditions the DRL lamps will illuminate.

Ground is applied at all times at G201 to the front fog lamp switch inside of the turn signal/multifunction switch. When the front fog lamp switch is placed in the ON position, ground is applied through the front fog lamp switch signal circuit to the body control module (BCM). The BCM applies battery voltage through the front fog lamp relay control circuit to the coil side of the fog lamp relay. Battery voltage is applied at all times from the FOG LP fuse to the switch side of the fog lamp relay. When the relay is energized, the relay switch contacts close and allow battery voltage to be applied from the FOG LP fuse, through the relay switch contacts, to the front fog lamps. Ground for the front fog lamps is applied at all times at G101 for the left fog lamp and G102 for the right fog lamp. G101 also serves as ground for the coil side of the fog lamp relay.

Ground is applied at all times from G201 to the rear fog lamp switch inside of the multifunction switch. When the rear fog lamp switch is placed in the ON position, a ground is applied through the rear fog lamp switch signal circuit to the body control module (BCM). Battery positive voltage is applied at all times from the REAR FOG/ALDL/TOP SW fuse to the BCM. The BCM then applies a battery positive voltage through the rear fog lamp relay control circuit to activate the rear fog lamp relay in the underhood electrical center. When the relay is activated it closes the switch and allows battery positive voltage to be applied from the RR FOG/ALDL/TOP SW Fuse, through the relay, to the rear fog lamps. The ground for the rear fog lamps is applied at all times from G301.

Battery positive voltage is applied at all times from the PARK LAMPS Fuse to both of the coil and switched sides of the PARK LAMP Relay in the underhood electrical center. Ground is applied from G201 to the multifunction switch at all times. When the headlamp switch is place in either the HEAD or PARK position, a ground is applied to the park lamp relay control circuit. This energizes the PARK LAMP Relay and applies battery positive voltage to all of the park, tail, license, and marker lamps. The ground for the front park lamps is supplied from G101 for the left and G102 for the right. The ground for the tail lamps and rear side marker lamps is supplied from G301 for the left and G302 for the right. The ground for the license lamps is supplied from G301. The ground for the front marker lamps is supplied from G101 for the left and G102 for the right.

Ground is applied at all times from G201 to the turn signal switch in the multifunction switch. When the turn signal switch is placed in either the TURN RIGHT or TURN LEFT position, a ground signal is applied to the body control module (BCM) through the either the right turn or left turn signal switch circuit. Battery positive voltage is applied at all times from the BATT MAIN 3 Fuse to the BCM. The BCM then applies a pulsating voltage to the front and rear turn signal lamps. The ground for the left front turn signal lamp is supplied from G101. The ground for the right front turn signal lamp is supplied from G102. The left rear turn signal lamp receives it ground from G301. The right rear turn signal lamp receives it ground from G302.

Ground as supplied at all times from G201 to the hazard switch. Battery positive voltage is applied at all times from the BATT MAIN 3 Fuse to the body control module (BCM). When the hazard switch is placed in the ON position, ground is applied through the hazard switch signal circuit to the BCM. The BCM then applies a pulsating voltage to all of the turn signal lamps. When the hazard warning switch is placed in the HAZARD position, the instrument panel (I/P) cluster applies a voltage through the hazard flash indicator circuit to the hazard warning switch to illuminate the hazard indicator.

The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5-volt reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery positive voltage to the stop lamps, transmission control module (TCM), engine control module (ECM), and stop lamp relay coil side. The BCM also supplies the stop lamp relay coil with ground. When the stop lamp relay receives battery voltage and ground from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage through the STOP/B/U/LPS fuse to illuminate the center high mounted stop lamp (CHMSL). Ground for the left stop lamp and CHMSL are provided at G301 and the right stop lamp receives ground at G302. The stop lamps on this vehicle will not illuminate unless the ignition is in the accessory, run, or crank positions. When the ignition is in the OFF position the stop lamps will not illuminate when the brake pedal is applied.

When the transmission is placed in the reverse position, a signal is sent to the transmission control module (TCM). The TCM then sends a class 2 signal to the body control module (BCM). Battery positive voltage is supplied from the STOP/B/U Fuse to the BCM. The BCM then applies battery positive voltage through the backup lamp supply voltage circuit to the backup lamps. Ground is applied for the backup lamps at all times from G301.