Voltage to the headlamp switch is available at all times from the HDLP SW fuse 7 through CKT 1940 (ORN). When the headlamp switch is turned to the HDLP position, the headlamp power relay coil is energized through CKT 352 (WHT). A signal is also sent to the body control module (BCM) that the headlamp switch is ON. When the headlamp switch is in the AUTO or PARK position, the ambient light sensor (located in the right speaker grill) senses either daylight or darkness and sends the signal to the BCM. When the Ambient Light Sensor detects a dark condition, the BCM produces a signal that will energize the headlamp power relay through CKT 352. The relay coil is grounded through terminal F7 connector 2 of the UBEC to CKT 350 (BLK) to G102. When the headlamp power relay is energized the relay supplies power to the LT HDLP and RT HDLP fuses. The RH low beam headlamp receives current through CKT 198 (DK BLU) from the RT HDLP fuse. The LH low beam headlamp receives current through CKT 712 (YEL/BLK) from the LT HDLP fuse. Both headlamp low beam bulbs are grounded by CKT 524 (PPL) through the UBEC to the multifunction switch (low position) contacts through CKT 10 (YEL) to the headlamp grounding relay in the body relay block through the normally closed contacts to CKT 1850 (BLK) to G200.

Voltage to the headlamp switch is available at all times from the HDLP SW fuse 7 through CKT 1940 (ORN). When the headlamp switch is turned to the HDLP position, the headlamp power relay coil is energized through CKT 352 (WHT). A signal is also sent to the body control module (BCM) that the headlamp switch is ON. The relay coil is grounded through terminal F7 connector 2 of the UBEC to CKT 350 (BLK) to G102. When the headlamp power relay is energized the relay supplies power to the LT HDLP and RT HDLP fuses. The RH high beam headlamp receives current through CKT 198 (DK BLU) from the RT HDLP fuse. When the headlamp switch is in the HDLP position, the BCM removes the ground path to the relay coils of the headlamp grounding relay and the DRL relay. Both relays return to the normally open position. The normally open contacts of the DRL relay allows current to the LH high beam headlamp through CKT 711 (DK GRN/WHT). Both high beam headlamps are grounded by CKT 524 (PPL) through the UBEC to the multifunction switch (high position) contacts through CKT 10 (YEL) to the headlamp grounding relay in the body relay block through the normally closed contacts to CKT 1850 (BLK) to G200. A voltage signal is sent to the BCM through CKT 524 (PPL) in order to confirm high beam operation.

The battery fuse supplies the following to cavity 87 and cavity 30 of the low beam relay:

The current is the power provided through the relay contacts to each HID ballast when the relay is closed. The low beam relay is controlled by a 12-volt input supplied to cavity 85 by one of the following components:

The relay coil is permanently grounded through cavity 86 at ground G102. When the headlamps are turned on, either from the headlamp switch or the BCM, the following actions occur:

Each ballast has a separate ground.

Ensure that 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 the 20 amps 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 from the -360 volt ballast output.) The input current during the steady state operation is 3.4 amps at 12.8 volts.

Normal operation of the HID system starts at the ballast. The 2 wires at the ballast input connector contain the +12 volt power supply and ground return. As soon as the input power is applied, the ballast draws 20 amp from the battery for 5-10 seconds (depending on the input voltage level). The ballast is then able to charge the two outputs leading to the start to -360 volts and +800 volts. -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.

After the lamp receives the strike from the starter and the arc is established, the ballast uses its -360 volt output 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 2 seconds of the arc being established in the bulb, 70% of steady state is complete. 100% of the steady state is completed within 30 seconds. A 75-watt power level is necessary in order to bring the lamp to a steady state in such a short period of time. The 75-watt power level allows the lamp to meet the SAE light vs. time specification.

Bulb failure (end of life) occurs when the bulb gets older 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 seconds. 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 (20 amp). 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.

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.