The exterior lighting system consist of the following lamps:

The headlamps may be turned on in two different ways. First, when the driver places the headlamp switch in the HEADLAMP position, for normal operation. Second, with the headlamp switch placed in the AUTO position, for automatic lamp control (ALC). During ALC control, the headlamps will be in daytime running lamp (DRL) operation in daylight conditions, or low beam operation in low light conditions.

Low Beams (Except Envoy, Diamond Edition with High Intensity Discharge (HID) Headlamps and ZR2)

Battery positive voltage to the headlamp switch is supplied by the HDLP SW fuse in the IP fuse block. When the headlamp switch is in the HDLP position, the headlamp power relay coil is energized. A voltage signal is also sent to the body control module (BCM) signaling that the headlamp switch is activated. The headlamp power relay coil is grounded at G102. When the headlamp power relay is energized, the relay supplies battery voltage to the LT HDLP and RT HDLP fuses. Both low beam headlamps are grounded by the multifunction headlamp dimmer switch in the low beam position through the normally closed headlamp grounding relay in the body relay block to G200.

Low Beams (Envoy and Diamond Edition w/HID)

Caution: The high intensity discharge system produces high voltage and current. To reduce the risk of severe shocks and burns:

The battery fuse supplies the following to the low beam relay located in the underhood fuse block:

The current is provided through the low beam relay contacts to each HID ballast when the relay is energized. The low beam relay is controlled by a battery positive voltage input from one of the following components:

G102 provides ground for the low beam relay. When the headlamps are turned on, either from the headlamp switch or the BCM, the following actions occur:

The LH headlamp ballast ground is at G109 while the RH headlamp ballast ground is at G113.

Electrical System Requirements

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 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 of operation is 3.4 amps at 12.8 volts.

Startup/Striking The Bulb

Normal operation of the HID system starts at the ballast. The 2 wires at the ballast input connector contain the battery positive voltage power supply and ground return. As soon as the input power is applied, the ballast draws 20 amps 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 arc tube. The creation of this arc begins the start up process.

Run Up Of The Lamp

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 arc tube, 70 percent of steady state is complete. 100 percent 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.

When To Change The HID Bulb

Bulb, or arc tube, failure 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. 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 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.

Low Beams (ZR2)

Battery positive voltage to the headlamp switch is supplied by the HDLP SW fuse in the IP fuse block. When the headlamp switch is in the HDLP position, the headlamp power relay coil is energized. A voltage signal is also sent to the body control module (BCM) signaling that the headlamp switch is activated. When the headlamp switch is in the AUTO or PARK position and the ambient light sensor detects darkness, the BCM produces a voltage signal that will also energize the headlamp power relay. The headlamp power relay coil is grounded at G102. When the headlamp power relay is energized, the relay supplies battery voltage to the LT HDLP and RT HDLP fuses. Both low beam headlamps are grounded by the multifunction headlamp dimmer switch in the low beam position through the normally closed daytime running lamp (DRL) relay to G102.

High Beams (Except Envoy, Diamond Edition w/HID and ZR2)

Battery positive voltage to the headlamp switch is supplied by the HDLP SW fuse in the IP fuse block. When the headlamp switch is in the HDLP position, the headlamp power relay coil is energized. A voltage signal is also sent to the body control module (BCM) signaling that the headlamp switch is activated. When the headlamp switch is in the AUTO or PARK position and the ambient light sensor detects darkness, the BCM produces a voltage signal that will also energize the headlamp power relay. The headlamp power relay coil is grounded at G102. When the headlamp power relay is energized, the relay supplies battery voltage to the LT HDLP and RT HDLP fuses. The RH high beam headlamp receives current directly from the RT HDLP fuse. When the headlamp switch is in the HDLP position, the BCM removes the ground path to the headlamp grounding and DRL relay coils. This allows current to flow to the LH high beam headlamp through the normally closed contacts of the DRL relay. Both high beam headlamps are grounded by the multifunction headlamp dimmer switch in the high beam position through the normally closed contacts in the headlamp grounding relay to G200. A ground signal is also sent to the BCM in order to confirm high beam operation.

High Beams (ZR2)

Battery positive voltage to the headlamp switch is supplied by the HDLP SW fuse in the IP fuse block. When the headlamp switch is in the HDLP position, the headlamp power relay coil is energized. A voltage signal is also sent to the body control module (BCM) signaling that the headlamp switch is activated. When the headlamp switch is in the AUTO or PARK position and the ambient light sensor detects darkness, the BCM produces a voltage signal that will also energize the headlamp power relay. The headlamp power relay coil is grounded at G102. When the headlamp power relay is energized, the relay supplies battery voltage to the LT HDLP and RT HDLP fuses. Both high beam headlamps are grounded by the multifunction headlamp dimmer switch in the high beam position through the normally closed contacts of the daytime running lamp (DRL) relay to G102.

High Beams (Envoy and Diamond Edition w/HID)

Battery positive voltage to the headlamp switch is supplied by the HDLP SW fuse in the IP fuse block. When the headlamp switch is in the HDLP position, a voltage signal is sent to the body control module (BCM) signaling that the headlamp switch is activated. When the headlamp switch is in the AUTO or PARK position and the ambient light sensor detects darkness the BCM switches to the ALC mode. Battery positive voltage to the high beam relay is available at all times from the HI BEAM fuse in the underhood fuse block. The high beam relay coil voltage is supplied by the BCM based on the headlamp switch, ambient light sensor and multifunction headlamp dimmer switch status. When the high beam relay coil is grounded by the multifunction headlamp dimmer switch in the high beams position to G200, the relay supplies battery voltage to the LH HI and RH HI fuses in the underhood fuse block. The high beam relay can also be activated by the BCM at any time if the BCM receives a voltage signal input from the multifunction headlamp dimmer switch when the momentary flash to pass function is activated. The LH high beam headlamp receives battery positive voltage directly from the LH HI fuse and is grounded at G111. The RH high beam headlamp receives battery positive voltage directly from the RH HI fuse. The DRL relay coil is supplied voltage by the IGN E fuse in the underhood fuse block. When the headlamp switch is in the AUTO position with the ambient light sensor detecting darkness or if the headlamp switch is in the HEAD position, the BCM removes the ground path to the DRL relay coil. This completes the ground circuit for the RH high beam headlamp through the normally closed contacts of the DRL relay to G102.

Headlamp Leveling (Export)

Voltage is supplied to the headlamp leveling switch through the IGN E fuse in the underhood fuse block. The headlamp leveling actuators are also powered by the same fuse but from a different terminal location in the underhood fuse block than the headlamp leveling switch. The headlamp leveling switch varies the amount of current to the actuators causing them to move simultaneously up or down to each selected position. Ground for the actuators and the switch are supplied by G203.

The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal it will either turn on the daytime running lamps (DRL) or the headlights for auto headlamp operation. Any function or condition that turns on the headlights will cancel the daytime running lamps operation. With the headlight switch in the OFF position, the headlights will either be turned ON or OFF, after an approximate 8 second delay depending on whether daylight or low light conditions are sensed. The DRL will operate when the ignition switch is in the RUN position, the gear selector is not in the PARK position and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.

DRL operation in Manual Transmission equipped vehicles will occur when the ignition switch is in the RUN position, and the parking brake is released.

The automatic lamp control (ALC) system and the daytime running lamps (DRL) feature (except the Canadian version) can be temporarily disabled by performing the following procedure:

1. Turn the ignition to RUN.
2. Press the DOME OVERRIDE button 4 times within 6 seconds.

A chime will sound informing you that the system is off. The system will remain disabled until the ignition is cycled off and then on or by pressing the DOME OVERRIDE button 4 more times within 6 seconds. The chime will sound again signaling that the system has been reactivated.

All (Except Envoy, Diamond Edition w/HID and ZR2)

The DRL relay is supplied battery positive voltage by the FOG LP fuse in the underhood fuse block. When the BCM requests DRL operation, the DRL relay coil and headlamp grounding relay coil are grounded by the BCM activating both relays. The energized headlamp grounding relay removes the ground utilized in normal headlamp operation to the multifunction headlamp dimmer switch . The energized DRL relay reroutes the LH high beam supply voltage circuit to ground at G102. These actions result in the LH and RH high beam headlamps to function in a series circuit at a reduced intensity.

On some vehicles, the DRL will turn OFF when the turn signal lamps are activated. This is controlled by the BCM and is a normal condition.

ZR2

On a vehicle with the ZR2 option, the daytime running lamps utilize the low beam headlamps equipped with a long life bulb in a parallel circuit. Voltage is supplied by the headlamp power relay as in normal low beam operation to each low beam headlamp bulb however the ground is controlled by the DRL relay. When the BCM requests for DRL operation, it will apply battery positive voltage energizing the headlamp power relay coil and ground activating the DRL relay coil. The DRL relay bypasses the multifunction headlamp dimmer switch completing the headlamp low beam ground circuit to G102. The parameters required to operate the system are the same as a vehicle without the ZR2 option.

Envoy and Diamond Edition w/HID

The DRL relay is supplied battery positive voltage by the IGN E fuse in the underhood fuse block. When the BCM requests DRL operation, the DRL relay coil is grounded by the BCM activating the relay. The energized DRL relay reroutes the RH high beam ground circuit to battery positive voltage supplied by the DRL fuse in the underhood fuse block. This action results in the LH and RH high beam headlamps to function in a series circuit at a reduced intensity.

With both the ignition switch in the RUN position, and the park lamps or low beam headlamps on, the fog lights and indicators will illuminate when the driver presses the fog lamp switch. The FOG LP fuse in the engine wiring harness junction block supplies battery positive voltage to the fog lamp relay for the fog lamp supply voltage circuit. The park lamp relay supplies battery positive voltage to the fog lamp relay coil. With the headlamp switch in either the park or headlamp position, and the fog lamp switch is pressed, a ground signal from G203 is sent to the body control module (BCM) requesting to ground the fog lamp relay control circuit energizing the relay. The current flow is from the fog lamp relay to both front fog lamps and to grounds G111 and G112. The state of the fog lamps will remain the same until the fog lamp switch is pressed again, or the ignition switch is cycled OFF and ON. Fog lamp operation will be cancelled whenever the park lamps, are turned OFF or the high beam headlights have been selected.

The export vehicle has only rear fog lamps and they are controlled in the same way. The ground for the rear fog lamps is supplied by G450.

The park, tail, marker and license lamps are turned on when the headlamp switch is placed in the PARK or ON position or anytime the headlights are requested. The PARK LP fuse in the engine wiring harness junction block supplies battery positive voltage to the park lamp relay coil and the headlamp switch. The body control module (BCM) provides a ground, or control circuit, to the park lamp relay coil circuit during ALC operation. When the park lamps are turned on during ALC, the BCM energizes the park lamp relay. The park lamps can also be supplied battery positive voltage directly from the headlamp switch. Current flow is to the FR PARK fuse, LR PARK fuse, RR  PARK fuse and the TRL PARK fuse, and to their respective park, marker and license lamps. The front park and marker lamps are grounded at G111 and G112. The rear park, tail, marker and license lamps are grounded at G475 and G422 on the pickup and G450 and G402 on the utility. If the headlight switch is left in the ON position, the park, tail and marker lamps will remain on until turned off or the battery runs dead.

The front side marker lamps on the export vehicle stay on steady and do not flash alternately with the turn signals as the domestic vehicle does due to they are grounded directly to G111 and G112.

The HAZ LP fuse in the underhood fuse block supplies battery positive voltage to the multifunction hazard switch assembly. The TURN fuse in the IP fuse block supplies Ignition positive voltage to the multifunction turn signal switch assembly. With the ignition switch in the RUN or START position, ignition positive voltage is connected through the multifunction turn signal and hazard switch assembly to the flasher module which is grounded at G205. When the turn signal switch is placed in either the left or right position, the circuit is complete from the flasher module to the turn signal lamps and to ground. The flasher module then sends an on-off voltage signal to either the left or right turn signals and their instrument panel cluster (IPC) indicator. When the hazard switch is activated, all turn signal lamps will flash including both IPC turn indicators. The front turn signals are grounded at G111 and G112. The rear turn signals are grounded at G475 and G422 on the pickup and G450 on the utility.

On the export vehicle, the rear turn signal lamps are separate amber lamps utilizing single filament bulbs grounded at G450. There are also amber side repeater lamps on each fender which are grounded at G111 and G112. The front side marker lamps stay on steady and do not flash alternately with the turn signals as the domestic vehicle does due to they are grounded directly to G111 and G112.

The STOP LP fuse in the engine wiring harness junction block supplies battery positive voltage to the normally open stop lamp switch. When the driver presses the brake pedal, the switch contacts close and battery positive voltage is supplied to both the VECHMSL fuse and the TRCHMSL fuse. On the pickup only, voltage is also supplied to the CHMSL relay in the underhood fuse block which energizes the relay. The energized CHMSL relay supplies battery positive voltage to the multifunction turn signal switch. The utility is not equipped with the CHMSL relay therefore battery positive voltage to the multifunction turn signal switch is supplied directly from the from the stop lamp switch. The current flow from the multifunction turn signal switch continues to the stop lamps which are grounded at G475 and G422 on the pickup and G450 on the utility. The center high mounted stop lamp (CHMSL) is grounded at G202 on the pickup and G450 on the utility.

The B/U fuse in the engine wiring harness junction block supplies battery positive voltage to the normally open backup lamp switch. When driver places the gear selector lever is in the REVERSE position, the backup lamp switch closes and the current flow is from the backup lamp switch through the VEH B/U fuse to the backup lamps. The backup lamps are grounded at G475 and G422 on the pickup and G450 on the utility.