GM Service Manual Online
For 1990-2009 cars only

Exterior Lamps

The exterior lighting consist of the following lamps:

    • The Headlamps
    • The Fog Lamps
    • The Park, Tail, License and Marker Lamps
    • The Turn Signal Lamps
    • The Stop Lamps
    • The Backup Lamps

Headlamps

The headlamps may be turned ON 2 different ways. First, when the driver places the headlamp switch is placed in the ON position, for normal operation. Second, with the headlamp switch placed in the OFF position, for automatic lamp control (ALC). During ALC control the headlamps will be in day time running lamp (DRL) operation in daylight conditions, or low beam operation in low light conditions.

For low beam operation, battery positive voltage is applied at all times to the coil and switch side of the low beam relay in the underhood fuse block. Ground is applied at all times from G202 to the headlamp switch. When the headlamp switch is placed in the HEAD position, ground is applied to the headlamps ON signal circuit to the body control module (BCM). When either the headlamp switch is placed in the HEAD position or ALC is enabled, the BCM applies a ground to the low beam relay control circuit. This energizes the relay and applies battery positive voltage to the LEFT and RIGHT low beam fuses in the underhood fuse block. Battery positive voltage is then applied from the fuses through the headlamp supply voltage circuit to the headlamps. Ground is applied at all times to the left headlamp from G101 and to the right headlamp from G100.

For high beam operation, battery positive voltage is applied at all times to the coil and switch side of the high beam relay in the underhood fuse block. Ground is applied at all times from G202 to the headlamp dimmer switch. When the dimmer switch is placed in the HIGH position, ground is applied to the high beam signal circuit to the BCM. The BCM then applies a ground to the high beam relay control circuit. This energizes the relay, and applies battery positive voltage to the LEFT and RIGHT high beam fuses in the underhood fuse block. Battery positive voltage is then applied from the fuses, through the high beam headlamp supply voltage circuit to the headlamps. Ground is applied at all times to the left headlamp from G101 and to the right headlamp from G100.

For flash-to-pass (FTP) operation, when the headlamp dimmer switch is placed in the FTP position, ground is applied from G202 through the headlamp dimmer switch to the flash-to-pass signal circuit to the BCM. The BCM then turns the high beam headlamps ON as long as the headlamp dimmer switch is in the FTP position.

If the headlight 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.

Lights On Warning

The body control module (BCM) activates the lights on warning as requested by the headlamp dimmer switch. The lights ON warning sounds when the following occurs:

    • The key is out of the ignition.
    • The BCM determines that the drivers door is open, signal is low.
    • The BCM determines that the headlamp switch is in the park or head position.

Daytime Running Lamps (DRL)

The ambient light sensor is a light sensitive transistor that varies its signal to the body control module (BCM) in response to changes to the outside ambient light level any function or condition that turns on the headlamps will cancel the DRL lamps 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 and the parking brake is not applied, or the transmission is not in PARK. When these conditions have been met and the ambient light sensor indicates daylight conditions, then the BCM will illuminate the front turn signal lamps ON steady.

Fog Lamps

The FOG LAMPS fuse in the underhood fuse block supplies battery positive voltage to the coil and switch side FOG LAMP relay in the underhood fuse block. When the fog lamp switch is placed in the ON position, ground is applied from G202 through the fog lamp switch to the body control module (BCM). The BCM then applies a ground to the FOG LAMP relay control circuit. This energizes the FOG LAMP relay, and applies battery positive voltage to the fog lamp voltage supply circuit. Ground is applied to the left fog lamp from G101 and to the right fog lamp from G100. The park lamps or low beam headlights must be ON in order for the fog lamps to illuminate. In addition, the BCM will send the serial data class 2 message to illuminate the fog lamp indicator in the IPC. Fog lamp operation will be cancelled whenever the park lamps are turned OFF or the high beam headlamps are turned ON.

Park, Tail, Marker and License Lamps

The PARK LAMPS fuse in the instrument panel (I/P) fuse block applies battery positive voltage to both the coil and switch side of the PARK LAMP relay in the I/P fuse block. When the headlamp switch is placed in either the PARK or HEAD position, ground is applied from G202 to the headlamp switch. The headlamp switch then applies the ground through the park lamp switch ON signal circuit to the body control module (BCM). The BCM then applies a ground to the PARK LAMP relay enable circuit. This energizes the PARK LAMP relay, applying battery positive voltage to all the park, tail, marker and license lamps. The park, tail, marker and license lamps are also turned ON when the headlamps are commanded ON by the BCM for low light operation.

Remote Keyless Entry Exterior Lamp Illumination

When the remote function actuation (RFA) module receives a door unlock command from the remote function actuator transmitter, the RFA module will ground the door unlock signal circuit to the body control module (BCM), send a class 2 message to the BCM, indicating that an UNLOCK command has been received. The BCM will then flash the park lamps twice. With all the doors closed, and the RKE transmitter is used to lock the doors, the park lamps will flash twice. The park lamps will not flash if the rear compartment is opened using the RKE transmitter.

Turn Signal Lamps

The STOP/TURN/HAZARD fuse in the instrument panel (I/P) fuse block supplies battery positive voltage to the body control module (BCM) for the turn signal lamps. When the turn switch is placed in the LEFT TURN or RIGHT TURN position, ground is applied from G202 through the turn switch, to the turn signal switch signal circuit and to the BCM. The BCM then applies battery positive voltage to front and rear turn signal lamps supply voltage circuits. The left front turn signal lamp is grounded at G100, right front at G101, left rear at G301 and the right rear is at G302.

Turn Signal Reminder

The driver information center (DIC) activates the turn signal warning as requested by either turn signal switch. The turn signal warning sounds when the following occurs:

    • The ignition is in RUN.
    • The turn signal switch is in either turn position, sensing, within 1 second, an open to battery positive voltage transition in the turn signal control circuit, left or right turn.
    • The vehicle has traveled a distance of 1.2 km (0.75 mi) by counting pulses in the rolling odometer class 2 message.

The DIC turns OFF the turn signal reminder when either the ignition switch is turned to the OFF position, or the turn signal switch returns to the OFF position, sensing within 1 second, no transitions from open to battery positive voltage in either of the turn signal control circuits, left turn or right turn.

Stop Lamps

The turn signal lamps are also used as stop lamps. The STOP/TURN/HAZARD fuse in the instrument panel (I/P) fuse block supplies battery positive voltage to the body control module (BCM) for the stop lamps.

A 10-volt reference signal and a low reference signal is applied from the BCM to the brake pedal position (BPP) sensor. When the brake pedal is applied, the BPP sensor applies a signal to the BPP sensor signal circuit to the BCM. The BCM then applies battery positive voltage to the LR and RR stop/tail/turn lamps through the LR and RR stop/turn lamps supply voltage circuit. The BCM also supplies a battery positive voltage to the CHMSL through the stop lamp supply voltage circuit. The ground for the LR stop/tail/turn lamp is supplied from G301 The ground for the RR stop/tail/turn lamp and for the CHMSL is supplied from G302.

Backup Lamps

The CHMSL/BACKUP fuse in the instrument panel (I/P) fuse block supplies battery positive voltage to the body control module (BCM). When the driver places the gear selection into the REVERSE position, the powertrain control module (PCM) sends a class 2 message to the BCM. The message indicates that the gear selector lever is in the REVERSE position. The BCM then applies battery positive voltage from the CHMSL/BACKUP fuse supply circuit to the backup lamps voltage supply circuit. Ground for the backup lamps is supplied from G302.

Battery Rundown Protection / Inadvertent Power

The body control module (BCM) used in this vehicle controls the lighting system through circuits that enable both the exterior lamp functions of park, head and fog lamps as well as the interior lamps. The BCM opens these enabling circuits 20 minutes after the ignition switch is turned OFF with no lamp switch activity. If the ignition switch is turned to any position other than OFF, or if a lamp switch is activated, during this 20 minute period the timer will reset for another 20 minutes.