For 1990-2009 cars

### Exterior Lamps

The exterior lighting consist of the following lamps:

• | Headlamps

• | Daytime running lamps (DRL)

• | Front Fog lamps

• | Park, tail, license and marker lamps

• | Turn signal lamps

• | Hazard warning lamps

• | Rear Fog lamp

• | Stop lamps

• | Backup lamps

### 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 two 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)

With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the turn signal/multifunction switch at G300. In response to this input, the body control module (BCM) 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 BCM 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. 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 left low and high beam headlamps are grounded at G101 and the right low and high beam headlamps are grounded at G102. When the headlamp dimmer switch lever is pulled toward the driver, the flash to pass (FTP) switch closes. This grounds the BCM flash to pass switch signal. In response to this input, the BCM 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 BCM 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.

### Automatic Lamp Control/Twilight Sentinel

Place the turn signal/multifunction 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 outside light level. The ambient light sensor is a light sensitive transistor that varies the voltage signal to the body control module (BCM). The BCM applies ground to the headlamp low beam relay control circuit which energizes the low beam relay, closing the switched side and applies battery voltage to the LEFT and RIGHT LOW BEAM fuses. Battery voltage is applied from the low beam fuses, through the low beam voltage supply circuits to the headlamp assembly. The ground for the headlamps is supplied from G101 for the left headlamp and G102 for the right headlamp.

### Flash to Pass (FTP)

When the low beam headlamps are on and the turn signal/multifunction switch is momentarily placed in the flash to pass (FTP) position, ground is applied from G300 to the turn signal/multifunction switch. The turn signal/multifunction switch applies ground to the body control module (BCM) through the FTP switch signal circuit. The BCM then applies 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 voltage to the LEFT and RIGHT HIGH BEAM fuses. Battery voltage is 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.

### Front Fog Lamps

When the front fog lamp switch is placed in the ON position, ground is applied through the front fog lamp switch signal circuit at G300 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 front fog lamp relay. Battery voltage is applied at all times from the FOG LAMP fuse to the switch side of the front fog lamp relay. When the relay coil is energized, the relay switch contacts close and allow battery voltage to be applied from the FOG LAMP 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 front fog lamp and G102 for the right front fog lamp. G102 also serves as ground for the coil side of the front fog lamp relay.

### Rear Fog Lamp

When the rear fog lamp switch is placed in the ON position, ground is applied through the rear fog lamp switch signal circuit at G300 to the body control module (BCM). The BCM applies ground through the rear fog lamp relay control circuit to the coil side of the fog lamp relay. Battery voltage is applied at all times from the REAR FOG LAMP fuse to the coil and switch sides of the fog lamp relay. When the relay coil is energized, the relay switch contacts close and allow battery voltage to be applied from the REAR FOG LAMP fuse, through the relay switch contacts, to the rear fog lamp. Ground for the rear fog lamp is applied at all times at G402.

### Park, Tail, License and Marker Lamps

Battery voltage is applied at all times from the PRK LAMPS fuse to both coil and switched sides of the PARK LAMP Relay located in the underhood fuse block. Ground is applied at G300 to the turn signal/multifunction switch at all times. When the headlamp switch is place in either the HEAD or PARK position, ground is applied to the park lamp relay control circuit. This energizes the PARK LAMP Relay and applies battery voltage to all park, tail, license, and marker lamps. Ground for the front park and marker lamps is supplied at G101 for the left and G102 for the right. Ground for the license, tail, and rear side marker lamps is supplied at G402 for the right and G400 for the left.

### Turn Signal Lamps

Ground is applied at all times at G300 to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START position. When the turn signal/multifunction switch is placed in either the TURN RIGHT or TURN LEFT position, ground is applied to the body control module (BCM) through either the right turn or left turn signal switch signal circuit. Battery 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. Ground for the left front turn signal lamp is supplied at G101. Ground for the right front turn signal lamp is supplied at G102. The left rear turn signal lamps are supplied ground at G400 and the right rear turn signal lamps are supplied ground at G402.

### Hazard Flasher Lamps

The hazard flashers may be activated in any power mode. The hazard switch is permanently grounded through G300. When the hazard switch is placed in the ON position, ground is applied through the hazard switch signal circuit to the body control module (BCM). The BCM supplies battery voltage to all four turn signal lamps in an ON and OFF duty cycle. When the hazard switch is placed in the ON position, the instrument panel cluster (IPC) receives a signal from the hazard switch and applies voltage through the hazard flash indicator circuit to the hazard switch to illuminate the hazard indicator.

### Stop Lamps

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, center high mounted stop lamp (CHMSL), transmission control module (TCM), and engine control module (ECM). Ground for the right rear stop lamp and CHMSL is applied at G402. Ground for the left rear stop lamp is applied at G400. 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.

### Backup Lamps

The underhood fuse block supplies battery positive voltage to the coil and switch terminals of the BACKUP LAMP relay. When the transmission is placed in the REVERSE position, the engine control module (ECM) sends a message via GMLAN to the body control module (BCM). The message indicates that the gear selector is in the REVERSE position. The BCM grounds the backup lamp relay control circuit of the backup lamps relay. This energizes the backup lamps relay, closing the switch side contacts and provides battery voltage to the BACKUP LAMP fuse through to the backup lamps. The backup lamps are permanently grounded at G402. With both power and ground the backup lamps illuminate. Once the driver moves the gear selector out of the REVERSE position, a message is sent by the ECM via GMLAN serial data requesting the BCM to remove ground from the backup lamp relay control circuit. This opens the backup lamps relay switch contacts turning OFF the backup lamps.