GM Service Manual Online
For 1990-2009 cars only

Exterior Lamps

The exterior lighting consist of the following lamps:

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

Headlamps

You can use the headlamps two different ways.

    • Place the headlamp switch in the HEAD position for normal operations
    • Place the headlamp switch in the OFF position for automatic lamp control (ALC) operation. During ALC the low beam headlamps are ON for daytime running lamp (DRL) operation in daylight conditions at reduced intensity or low beam headlamps ON at full intensity with exterior park lamps ON in low light conditions.

The body control module (BCM) applies a pulse width modulated (PWM) voltage to the headlamp module and high beam relay in the underhood fuse block. The ground for the headlamp module is supplied from G113 or G115. For normal manual low beam operation when the headlamp switch is place in the HEAD position, ground from G202 is applied through the headlamp switch and to the BCM through the headlamp switch headlamps ON signal circuit. The BCM then applies a PWM voltage to the headlamp module/high beam relay voltage supply circuit. The headlamp module then applies battery positive voltage through the left front (LF) and right front (RF) LO Beam fuses to the left and right low beam headlamps. The ground for the left headlamps is supplied by G101 and the ground for the right headlamp is supplied by G100.

For high beam operation, ground is applied at all times to the headlamp dimmer switch from G202. When the headlamp dimmer switch is placed in the HIGH position, ground is then applied through the headlamp dimmer switch signal circuit to the BCM. The BCM then applies a ground to the headlamp high beam relay control circuit. This energizes the HI Beam relay, the relay then applies battery positive voltage through the LF and RF HI BEAM fuses to the LF and RF high beam headlamps. The ground for the left headlamps is supplied by G101 and the ground for the right headlamp is supplied by G100.

The BCM then sends a class 2 message to the instrument cluster in order to illuminate the high beam indicator lamp. If the headlamp switch is left in the HEAD position, the inadvertent power control feature will turn OFF the headlamps after 10 minutes after you turn the ignition switch to the OFF position. If you place the headlamp switch in the head position after the ignition switch has been turned OFF, or if the ignition switch is in ACCY position, the headlamps will remain ON until you turn them OFF or until the battery runs dead.

HDLPS Suggested Indicator

If the park lamps are turned ON manually and the ambient light sensor detects a low light condition then the body control module (BCM) will send a class 2 message to the instrument panel cluster (IPC) to illuminate the HDLP suggested indicator.

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 voltage signal to the body control module (BCM) in response to changes in the outside (ambient) light level. When the BCM receives this signal the BCM turns ON just the low beam headlamps at reduced intensity for the daytime running lamp (DRL) operation. A resistor wire is used (CKT312) to reduced the voltage which reduces the light intensity for the DRL's function. The ambient light sensor can also turn ON the low beam headlamps and the exterior lamps for automatic lamp control (ALC). Any function or condition that turns ON the headlamps will cancel the DRL operation (this means no reduced voltage to the low beam lights). Thirty seconds after you start the engine with the headlamp switch in the OFF position, the DRL will perform one of two actions:

    • Illuminate the low beam headlamps at reduced intensity in daylight conditions
    • Illuminate the low beam headlamps and exterior park lamps for low light conditions

The DRL operates when the ignition switch is in the RUN position, the parking brake is not set and the transmission is not in the PARK position When these conditions are met and the DRL ambient light sensor indicates daylight conditions the DRL will illuminate

Fog Lamps

The FOG LPS fuse in the underhood fuse block supplies battery positive voltage to both the coil and switch side of the FOG LP Relay. 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 LP relay and applies battery positive voltage through the fog lamp voltage supply circuit to the left and right fog lamps. Ground is applied at all times to the left fog lamp from G101 and to the right fog lamp from G100. The park lamps are headlamps must be ON in order for the fog lamps to illuminate. Fog lamp operation will be cancelled whenever the park lamps are turned OFF or the high beams are turned ON. When the park lamps are turned ON, the BCM sends a class 2 message to the instrument panel cluster (IPC) to illuminate the fog lamp indicator.

Park, Tail, Marker and License Lamps

The LT PRK LAMP and RT PK LAMP fuses in the rear fuse block applies battery positive voltage to both the coil and switch side of the PARK LAMP Relay. The park lamp switch on signal circuit is grounded when the head lamp switch is in the head, park or auto position for low light operation. When the BCM receives the ground input from the park lamp switch on signal circuit the BCM then applies ground to the park lamp relay control circuit. This energizes the Park Lamp Relay, applying battery positive voltage to all the park, tail marker and license lamps.

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 to the body control module (BCM), then send a class 2 signal to the BCM indicating that an UNLOCK command has been received. The BCM then will flash the park lamps twice. With all the doors closed, and the remote keyless entry (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 TURN/HAZ fuse in the instrument panel (I/P) fuse block supplies battery positive voltage to the body control module (BCM) for the turn signal lamps and hazard lamps. When the turn signal switch is place in either the TURN LEFT or TURN RIGHT position, ground is applied from G202 through the turn signal switch to the BCM the BCM then applies battery positive voltage to the front and rear turn signal lamps supply voltage circuits. The left front turn signal lamp is grounded at G101 and the right front at G100. The left rear turn lamp is grounded at G301 and the right rear at G302.

Turn Signal Reminder

The body control module (BCM) 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 the RUN position.
    • The turn signal switch is in either turn position, sensing, within one 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 ON the vehicle speed input circuit.

The BCM 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.

Hazard Lamps

The TURN/HAZ fuse in the instrument panel (I/P) fuse block supplies battery positive voltage to the body control module (BCM) for the turn signal lamps and hazard lamps. When the hazard switch is placed in to the ON position, the driver information center (DIC) sends a signal to the BCM through he hazard switch signal circuit. The BCM then flashes all of the turn signal lamps ON and OFF.

Stop Lamps

The rear turn signal lamps are also used as the stop lamps. The TURN/HAZ fuse in the instrument panel (I/P) fuse block supplies battery positive voltage to the body control module (BCM) for the turn signal/stop lamps and hazard lamps. The CHMSL/BKUP fuse in the I/P fuse block provides battery positive voltage to the center high mounted stop lamp (CHMSL). The brake pedal position sensor receives a low reference signal and a 10-volt reference signal from the BCM. Whenever the brake pedal is applied, the brake pedal position sensor applies a variable voltage signal to the BCM through the stop lamp switch signal circuit. The BCM then applies battery positive voltage to the rear turn/stop lamps and to the CHMSL, illuminating them. The left rear turn lamp is grounded at G301 and the right rear stop/turn lamp and CHMSL is grounded at G302.

Backup Lamps

The CHMSL/BKUP 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 selector in to the REVERSE position, the powertrain control module (PCM) sends a class 2 message to the BCM. The BCM then applies battery positive voltage to the backup lamp supply voltage circuit. The left backup lamp is grounded at G301 and the right backup lamp is grounded at 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.