GM Service Manual Online
For 1990-2009 cars only

Exterior Lamps

The exterior lighting system includes the following components:

    • Headlamps (high and low beam)
    • Front park/turn signal lamps
    • Front cornering lamps
    • Tail/rear turn signal lamps
    • Front sidemarker lamps
    • Rear sidemarker lamps
    • High-mounted stop lamps
    • Backup lamps
    • Rear license lamps

This system also includes all wiring controls and related hardware required for the operation of these lamps.

Headlamps

The headlamps may be turned on two different ways. First, when the driver places the headlamp switch in the ON position, for normal operation. Second, with the headlamp switch placed in the OFF position, during Daytime Running Lamp (DRL) operation in low light conditions.

The HDLP L and HDLP R fuse in the fuse block - underhood, supply battery positive voltage to both low beam lamps and high beam lamps at all times. The low beam and high beam circuits continue to the headlamp dimmer switch , the low beam or high beam circuit is then, depending on the position of the dimmer switch, connected to the headlamp switch. When the headlamp switch is placed in the ON position, it provides a ground path for the low beam or high beam lamps through G201. The headlamp switch also provides a input signal to the BCM in order to determine if the headlamps are ON.

During automatic headlamp operation in low light conditions the BCM will pull the automatic headlamp relay low, energizing it. When the headlamp relay energizes, it provides a ground path for the low beam or high beam lamps through G201, depending on the dimmer switch position.

Both the headlamp switch and the automatic headlamp relay can provide a ground for the headlamps for manual or automatic headlight operation. The headlights may be switched to high beam by pulling the dimmer switch handle toward the driver until the high beam dimmer switch is activated. When the dimmer switch is placed in the HIGH BEAM position, the indicator lamp and the high beam lamps are grounded and illuminate.

Flash to Pass

The flash to pass feature can be operated with the low beams OFF or ON. The high beams may be momentarily turned on or flashed with the dimmer switch handle. When the headlamp dimmer switch handle is pulled toward the driver, the flash-to-pass switch closes grounding the high beam circuit at G201, both high beams will remain on until the driver releases the switch handle. If the low beam headlamps were on during a flash-to-pass operation, they will remain on.

Daytime Running Lamps (DRL)

The front turn signal lamps are used as both Daytime Running Lamps and turn signals lamps. The Body Control Module (BCM) illuminates the front turn signals lamps in a non flashing mode for Daytime Running Lamps (DRL) operation. If the turn signal switch is activated during Daytime Running Lamp operation, the appropriate turn signal will flash.

The Daytime Running Lamps (DRL) are designed to be automatically illuminated when the ignition is ON and the outside (ambient) light level is high as in daytime conditions (day mode). The Daytime Running Lamps (DRL) will not operate if the ambient light levels are too low (night mode). Light levels are detected by the ambient light sensor, a light sensitive transistor that varies its voltage signal to the Body Control Module (BCM) in response to changes to the ambient light level. When the BCM receives a day mode signal from the ambient light sensor it will then illuminate the DRL lamps. The automatic headlamps and park lamps will not operate when the DRL lamps are on.

In the day mode, the ambient light sensor detects daylight and the BCM applies voltage to the LH and RH front turn signal lamps illuminating the lamps under the following conditions:

    • The ignition switch is in the RUN position.
    • The headlamps are OFF.
    • The park brake is OFF (released).
    • The RH or LH turn signal is OFF.

Automatic Headlamps and Park Lamps

The automatic headlamps and park lamps are designed to automatically illuminate when the ignition is ON and the outside (ambient) light level is low as in night time conditions (night mode). Light levels are detected by the ambient light sensor, a light sensitive transistor that varies its voltage signal to the Body Control Module (BCM) in response to changes to the ambient light level. When the BCM receives a low light mode signal from the ambient light sensor it will then energize the park lamp and automatic headlamp relays illuminating the headlamps and park lamps. The DRL lamps will not operate when the automatic headlamps and park lamps are on.

In the low light mode, the ambient light sensor detects low light level, the BCM turns OFF the front turn signal lamps and grounds the park lamp relay and automatic headlamp relay control circuits, turning ON the headlamps and park lamps under the following conditions:

    • The ignition switch is in the RUN position.
    • The headlamps are OFF.
    • The park brake is OFF (released).

If the engine stalls with the DRL in the low light mode, the BCM turns OFF the headlamps while the engine is being cranked. The park lamps will remain ON while the engine is being cranked.

Delayed Headlamp Control

The BCM has a delayed headlamp control feature that will leave the headlamps ON for a 90 seconds after the ignition switch is turned OFF, when the automatic headlamp are on and the headlamp switches is in the OFF position.

Park Brake Input

The BCM will not operate any headlamps or exterior lamps, if the park brake is applied before the ignition switch is turned to the RUN position. This allows the driver to start the vehicle and keep the headlamps OFF, as long as the park brake is applied. The BCM will activate the headlamps when the park brake is released with the ignition switch in the RUN position. This feature functions only when the park brake is applied before the ignition switch is turned to the RUN position. The headlamps will not turn OFF, if the park brake is applied after the ignition switch is turned to the RUN position.

Fog Lamps

The fog lamps are located in the bumper fascia beneath the headlamp assemblies. The front fog lamp switch is located below the headlamp switch on the left side of the Instrument Panel Cluster (IPC). Pressing the fog lamp switch button will turn the fog lamps ON, as long as the headlamp switch is NOT in the OFF position. When the fog lamps are ON, an indicator on the fog lamp switch will illuminate. Pressing the switch again will turn the fog lamps OFF.

The FOG LAMP relay in the fuse block - underhood controls the fog lamps. The switched side of the relay receives battery voltage at all times from the FOG LP Fuse. The coil side feed circuit of the fog lamp relay receives voltage from the HDLP fuses via an inactive high beam headlamp. The voltage will be pulled low with the high beams ON disabling the fog lamps. The BCM will provide an enable signal to the fog lamp switch when the ignition is ON and the headlamp switch is in PARK or HEAD position. With the fog lamp enable circuit active and the fog lamp switch is pressed, a ground is applied to the fog lamp relay control circuit. This energizes the relay, closing the switched contact and applying battery voltage to the fog lamps. The fog lamps receive a constant ground.

Turn Signal Lamps

The front turn signal lamps are made up of the front park/turn signal lamps and rear turn signal lamps. The front turn signal lamps flash with the rear turn signal lamps when a turn is initiated using the turn signal/multifunction lever. The turn signals will operate only with the ignition switch in the RUN position and will not operate during hazard flasher operation.

When the ignition is turned to the RUN position, battery voltage is supplied to the TURN SIGNAL Fuse. Battery voltage is then applied through the turn signal fuse circuit to the turn signal switch. When the turn signal switch is placed in the LH or RH position, voltage is supplied to the hazard lamp/turn signal lamp flasher. The hazard lamp/turn signal lamp flasher supplies a turn signal flasher signal to the turn signal switch. With the turn signal switch in the LH or RH position the corresponding turn signal indicator, rear turn signal, and front turn signal receive the turn signal switch signal and will flash. The front turn signals receive the turn signal switch signal from the turn signal switch via the BCM. The turn lamps are permanently grounded.

Hazard Lamps

The hazard warning switch is part of the turn signal switch. The turn signal switch receives battery voltage at all times through the HAZARD SWITCH Fuse. When the hazard switch is placed in the HAZARD position, battery voltage is applied to the hazard lamp/turn signal lamp flasher. The hazard lamp/turn signal lamp flasher sends a turn signal flasher signal to the turn signal switch. The turn signal switch provides all of the turn lamps and turn indicators with the turn signal flasher signal, simultaneously flashing them on and off.

Cornering Lamps

The front cornering lamps are located outboard of the low-beam headlamp bulb in each of the headlamp assemblies. The cornering lamps operate when a turn is initiated using the turn signal/multifunction lever. The cornering lamps will operate only with the ignition switch in the RUN position and will not operate during hazard flasher operation.

The TURN SIGNAL CORN LPS fuse supplies voltage to the turn signal switch when the ignition is in RUN. When the turn signal switch is placed in the LH or RH position the corresponding cornering lamp will receive voltage and illuminate. The cornering lamps are permanently grounded.

Park, Tail, Sidemarker, and Rear License Lamps

The front park lamps are made up of the front park/turn signal lamps and the front sidemarker lamps. The rear park lamps are made up of the rear tail/turn signal lamps, rear park lamps, rear sidemarker lamps, and rear license lamps.

The headlamp switch is used to operate all the park lamps and rear license lamps. The headlamp switch is located on the left side of the Instrument Panel Cluster (IPC). Pulling the knob of the headlamp switch out to the middle position will turn ON the park lamps. The park lamps can also be illuminated by the BCM during automatic headlamp operation in low light mode.

When the headlamp switch placed in the PARK position battery voltage is supplied through the headlamp switch to both the TAIL LAMP, LIC LAMPS fuse and the FRONT PARK fuse. Battery voltage is then applied through the TAIL LAMP LIC LAMPS fuse and the FRONT PARK fuse to the front and rear park lamps and the rear license lamps illuminating the lamps. The park lamps and rear license lamps receive ground at all times.

The park lamps can also be controlled by the park lamp relay during automatic headlamp operation in low light mode. Both the coil and the switched sides of the park lamp relay receive battery voltage at all times. When the BCM is in automatic headlamp operation, low light mode, the BCM then applies a ground through the park lamp relay coil control circuit to the park lamp relay. This energizes the relay closing the switch contact and applies battery voltage to both the TAIL LAMP, LIC LAMPS fuse and the FRONT PARK LAMP fuse. Battery voltage is then applied through the TAIL LAMP LIC LAMPS fuse and the FRONT PARK fuse to the front and rear park lamps and the rear license lamps illuminating the lamps. The park lamps and rear license lamps receive ground at all times.

Stop Lamps

The stop lamps consist of the center high mounted stop lamps and the LH and RH rear stop/turn lamps. The LH and RH rear stop/turn lamps are single- filament bulbs that are used as stop lamps and turn signal lamps.

The stop lamp switch receives battery voltage at all times through the STOP LAMPS fuse. When the brake pedal is pressed, the stoplamp switch closes and battery voltage is applied to the center high mounted stop lamps through the stop lamp switch signal circuit. The stop lamp switch signal circuit also sends battery voltage to the turn signal switch. The turn signal switch applies voltage to the rear stop/turn lamps through the turn signal lamp signal circuit, using the stop/turn signal lamps as stop lamps. The center high mounted stop lamp and the stop/turn signal lamps are permanently grounded.

Backup Lamps

The backup lamps are located in the rear compartment lid applique. The backup lamps operate when the ignition switch is in the RUN position and the transaxle range selector lever is in REVERSE.

The R/CMPT REL fuse supplies battery voltage at all the times to the coil side and the switched side of the backup relay. When the vehicle is placed in REVERSE, a class 2 signal is sent to the BCM. The BCM then applies a ground through the backup lamp relay coil control circuit to the backup lamps relay. This energizes the relay and allows battery positive voltage to be applied to the backup lamps turning them on. The backup lamps receive a constant ground signal

Lighting System Indicator(s)

High Beam

The high beam indicator is hard wired to the headlamp switch. The high beam indicator illuminates when the headlamp switch is in the high position (signal circuit is low).

Turn Signals

The left and right turn signal indicators are hard wired to the turn signal switch and the hazard switch. The turn signal indicator illuminates when the turn signal lamps supply voltage circuit is active. The body control module (BCM) is also hard wired to the turn signal switch. If the BCM determines that the turn signal flasher signal circuit is active for more than 1.2 km (0.75 mi), the BCM activates an audible warning.

Driver Controls and Modules

The Body Control Module (BCM) module processes the inputs and the controls. The ambient light sensor supplies the BCM with a signal for daytime conditions or for low light conditions:

    • The Body Control Module (BCM)
    • The ambient light sensor
    • The Instrument Panel Cluster (IPC)

Driver controls include the following components:

    • The fog lamp switch
    • The door lock switches
    • The headlamp dimmer switch
    • The headlamp switch
    • The park/neutral position switch
    • The park brake indicator switch
    • The stop lamp switch
    • The turn signal switch