GM Service Manual Online
For 1990-2009 cars only

Exterior Lamps

The exterior lighting consist of the following lamps:

    • Backup lamps
    • Daytime running lamps (DRL) and twilight sentinel
    • Headlamps
    • Park, tail, license and marker lamps
    • Turn signal/cornering lamps
    • Remote keyless entry exterior lamp illumination/perimeter lighting
    • Stop lamps

Backup Lamps

The B/U LP fuse in the fuse block - I/P supplies battery positive voltage to the control and to the switch terminals of the PERIM LP relay. When the driver selects the REVERSE position, the powertrain control module (PCM) sends a class 2 message to the remote control door lock receiver (RCDLR). The message indicates that the gear selector lever is in the REVERSE position. The RCDLR then energizes the PERIM LP relay and the backup lights illuminate. Current flows from the reverse lamp relay switch to the backup lamps. The backup lamps have ground at G400.

Daytime Running Lamps (DRL) and Twilight Sentinel

Twilight sentinel is a driver convenience that controls the exterior lamps in response to changes to the outside, ambient light level. The ambient light sensor is a light sensitive transistor that varies its voltage signal to the lamp control module (LCM) in response to changes to the outside, ambient light level. When the twilight switch is in ON, the LCM either turns on the DRL or turns on the low beam headlights, after a 20 second delay depending on whether daylight or low light conditions are sensed. Any function or condition that turns on the headlights will cancel the DRL operation. Battery positive voltage is supplied to the left high beam ground circuit from the LCM. When the LCM energizes the left high beam ground circuit, the current flows from the LCM switch to the left high beam. After the left high beam, the current flows through the left high beam fuse and through the right high beam fuse. The current continues through the right high beam to ground G105. Now, the high beam headlamps are in series, and split the voltage. The headlamps illuminate at half intensity. The DRL operate when the ignition switch is in the RUN position, and the parking brake is not set or the transmission is not in park. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.

Headlamps

The headlamps may be turned ON in 3 different ways:

    • When the headlamp switch is placed in the ON position, for normal operation.
    • With the twilight switch placed in the ON position, for automatic lamp control (ALC).
    • With the twilight switch placed in the ON position, with the windshield wipers ON in daylight conditions, after a 6 second delay. 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.

The lamp control module (LCM) provides battery positive voltage to the signal circuits of the headlamp switch and headlamp dimmer switch. The circuits include the headlamp switch headlamps on signal, the headlamp switch flash-to-pass signal and the headlamp dimmer switch high beam signal. When the headlamp switch is ON, a ground path is available for the headlamp switch headlamps on signal circuit of the LCM through the headlamp switch. The LCM provides battery voltage to the headlamp low beam supply voltage circuit or the headlamp high beam supply voltage circuit, if the headlamps are necessary. The position of the headlamp dimmer switch determines which circuit has battery voltage. When the headlamp low beam supply voltage circuit is energized, current flow goes to both low beam fuses. Current flows to the low beam headlamps. The headlamps have ground at G105 and at G106. When the headlamp high beam supply voltage circuit is energized, current flow goes to both high beam fuses. Current flows to the high beam headlamps. The current flow of the left high beam is from the fuse to the left high beam lamp. From the lamp, the current flows to G106 with T62 or the LCM without T62. The current flow of the right high beam is from the fuse to the right high beam lamp. From the lamp, the current flow is to ground at G105.

Park, Tail and Marker Lamps

The park lamps, including the license lamps and rear door window switch backlighting are turned ON when the headlamp switch is placed in the PARK , ON position or anytime the headlights are requested. The PK LP fuse in the fuse block - left underhood supplies battery positive voltage to the LCM. When the headlamp switch is in PARK or ON, the park lamp switch signal on circuit of the LCM has a ground path. The LCM provides battery positive voltage to the park lamp supply voltage circuit. When the park lamps and/or the tail lamps are ON, the LCM energizes the park lamp supply voltage circuit. Current flows from the LCM to the LP PK L fuse and to the LP PK R fuse in the fuse block - I/P. From the fuses, the current flows to the park lamps. The left park lamps are grounded at G106 and G402. The right park lamps are grounded at G105 and G400. The LP PK R fuse supplies park lamp supply voltage to the license lamps and the right rear door window switch backlighting lamp. The license lamps are grounded at G400. The LP PK L fuse supplies park lamp supply voltage to the left rear door window switch backlighting lamp.

Remote Keyless Entry Exterior Lamp Illumination/Perimeter Lighting

Perimeter lighting provides a personal security feature. The perimeter lighting feature illuminates the exterior lights on the outside of the vehicle for 15 seconds when the keyless entry transmitter is used to unlock the doors under night time conditions. The following lamps illuminate when the perimeter lighting is activated:

    • Backup lamps
    • Headlamps
    • Park lamps

When you press the UNLOCK button on the keyless entry transmitter, the remote control door lock receiver (RCDLR) grounds the headlamp alarm signal circuit to the lamp control module (LCM). The LCM then provides battery positive voltage to the headlamps and the park lamps. The RCDLR provides ground for the PERIM LP relay exterior courtesy lamps relay control circuit. The coil energizes and the switch contacts close providing supply voltage to the backup lamps.

Turn Signal/Cornering Lamps

The HZDT/SIG fuse in the fuse block - left underhood supplies battery positive voltage to the turn signal/hazard flasher module and have ground at G202. The turn signal lamps may only be activated with the ignition switch in the ON or ACCY position. The T/SIG fuse in the fuse block - left underhood supplies battery positive voltage to the turn signal/multifunction switch. When the turn signal/multifunction switch is placed in either the left or right position, current flow is from the turn signal/multifunction switch assembly to the turn signal/hazard flasher module. The turn signal/hazard flasher module then sends an on-off voltage signal to either the left or right turn signals and their instrument cluster (IPC) indicator. When the hazard switch is pressed, all the turn signal lamps will flash including both IPC turn signal indicators. The left turn signals have ground at G106, G400 and at G402. The right turn signals have ground at G105 and G400. The turn signal/multifunction switch supplies battery positive voltage to the cornering lamps, the left cornering lamp has ground at G106 and the right cornering lamp has ground at G105.

Stop Lamps

The STOP fuse in the fuse block - left underhood supplies battery positive voltage to the normally open stop lamp switch. When the driver presses the brake pedal, the switch contacts close. The battery positive voltage flows to the left stop lamp assemblies, to the right stop lamp assemblies, and to the center high mounted stop lamp (CHMSL). The left, the right stop lamp and the CHMSL have ground at G400 and G402.

Lighting System Indicators

    • High Beam
        The lamp control module (LCM) illuminates the high beam indicator in the IPC when the LCM detects that the high beams are requested. The IPC sends a class 2 message to the BCM indicating the status of the indicator.
    • High Beam (with HUD)
        The head up display (HUD) illuminates the high beam indicator when the IPC sends a signal requesting illumination.
    • 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. If the IPC determines that the turn signal is active for more than 1.29 km (0.8 mile), the IPC sends a class  2 message to the BCM in order to activate an audible warning.
    • Turn Signals (with HUD)
        The head up display (HUD) illuminates the turn signal indicators when the IPC sends a signal requesting illumination.

Battery Run Down Protection/Inadvertent Power

To provide battery run down protection the body control module (BCM) used in this vehicle controls the lighting system through circuits that enable both the exterior lamp functions of park lamp and headlamp as well as the interior lamps. The BCM opens these enabling circuits 10 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 10 minute period the timer will reset for another 10 minutes.

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.

The inadvertent power control feature prevents the park lights from remaining ON more than 10 minutes if left ON. If the park lights are turned ON after the ignition switch has been turned OFF, or is in the ACCY position, they will remain ON until turned OFF or the battery runs dead.