GM Service Manual Online
For 1990-2009 cars only

Interior Lamps

The interior lighting consist of two groups. This first group includes lamps that may not be dimmed.

    • The Inside Rearview Mirror Lamps
    • The Rear Compartment Courtesy Lamp
    • The Vanity Mirror Lamps
    • The IP Compartment Lamps
    • The Instrument Panel (IP) Courtesy Lamps
    • Underhood Lamp

Courtesy Lamps

The courtesy lamps include the instrument panel courtesy lamps, the rear compartment courtesy lamps, and the rear view mirror lamps. Turn the courtesy lamps ON manually by placing the interior lamp switch in the DOME position. If low light levels are detected by the ambient light sensor, then whenever a door or if the trunk is opened the courtesy lamps will illuminate. After all the doors have been closed the courtesy lamps will remain illuminated approximately 15 seconds after the last door closes.

The C\LALDL fuse in the instrument panel electrical center supplies battery positive voltage to the coil and switch side of the CTSY LP relay 42. The BCM controls the ground to the CTSY LP relay 42 coil side. When any door or if the trunk is opened, the jam switch contacts close and the BCM receives a door-open or trunk open input. If the BCM receives a door lock or unlock input or an trunk open input and it is a low light condition then the BCM will activate the CTS LP 42 relay providing battery positive voltage to all of the interior courtesy lamps. You may use some of the courtesy lamps as reading lamps by placing the lamp switch in the ON position.

The courtesy lamps will normally turn OFF using the theater dimming feature. The BCM provides a pulse width modulated ground to all courtesy/reading, dome and inside rear view mirror lamps for the theater dimming feature. The BCM turns OFF the courtesy lamps if a door lock command is received after all of the doors are closed, or if the ignition switch is turned to either the ON or RUN position.

The courtesy lamps will also turn on after an air bag deployment for approximately 15 seconds.

Keyless Entry Interior Illumination

When the driver uses the door key in order to unlock the doors, BCM receives a door-unlock signal. The BCM must have inputs that indicate that the ignition switch is OFF, the courtesy lamp switch is OFF and all the doors are closed. The BCM will then activate the interior lamps. The courtesy lamps will remain ON for 15 seconds after the door is closed. The BCM will turn off the courtesy lamps through the theater dimming feature. If the door locks are activated to the LOCK position, or if the ignition switch is turned to either the RUN or CRANK position, the courtesy lamps will turn OFF immediately.

When the driver uses the remote function actuator transmitter to unlock the doors or the trunk or to press the panic button, the BCM will keep the courtesy lamps ON for 30 seconds. If the door locks are activated to the UNLOCK or LOCK position, or if the ignition switch is turned to either the RUN or CRANK position, the courtesy lamps turn OFF immediately. The BCM keeps the courtesy lamps on for 40 seconds after an alarm event is completed.

Vanity Lamps

Battery positive voltage is applied at all times to the MONITORED LD relay 37 coil and switch side. The BCM applies a ground to the MONITORED LD relay 37 coil side, energizes the relay, and closes the switch contacts. Then the BCM allows battery positive voltage to the MONITORED LD fuse 2 and to the vanity mirror lamps. When the vanity mirror cover on the sunshade is opened, its switch closes providing a ground circuit, and the vanity lamp illuminates.

IP Compartment Lamp

Battery positive voltage is applied at all times to the MONITORED LD relay 37 coil and switch side. The BCM applies a ground to the MONITORED LD relay 37 coil side, energizes the relay and closes the switch contacts, The BCM then allows battery positive voltage to the MONITORED LD fuse 2 and then the IP compartment lamp. When the IP compartment is opened, its switch closes providing a ground circuit, and the IP compartment lamp illuminates.

Underhood Lamp

Battery positive voltage is applied at all times to the MONITORED LD relay 37 coil and switch side. The BCM applies a ground to the MONITORED LD relay 37 coil side, energizes the relay and closes the switch contacts. The BCM then allows battery positive voltage to the MONITORED LD fuse 2 and the underhood lamp. When the underhood is opened, its switch closes providing a ground circuit, and the underhood lamp illuminates.

Interior Lamps Dimming

The second group includes lamps which may be dimmed. This group may use a combination of vacuum fluorescent (VF) illumination and of incandescent lamps:

    • The Door Switches and the Window Switches
    • The HVAC Control Head Assembly
    • The Radio
    • The Traction/Suspension Control Switch
    • The PRNDL
    • The Fog Lamp\Rear Compartment Lid Release Switch (Domestic)
    • The Front and Rear Fog Lamp Switch (Export)

When the ignition switch is turned to the ON position, the vacuum fluorescent (VF) displays, for radio and HVAC control assembly, and the incandescent lamps turn ON at maximum brightness. When the park lamps are ON and the ambient light sensor indicates low light conditions, all incandescent back lighting turn ON at the dimming level indicated by the IP dimmer switch. At the same time all VF displays dim in order to match the indicated dimming level. The PK\LP fuse 6 in the instrument panel electrical center supplies battery positive voltage to both the ALC PRK LP relay switch and coil contacts. The ALC PRL LP relay coil is controlled by the BCM. When the headlamp switch is placed in the PARK position, the BCM energizes the park lamp relay coil control circuit and dims the interior lamps to the dimming level indicated by the IP dimmer switch. When the driver selects a dimming setting by moving the IP dimming switch potentiometer, all incandescent back lighting lamps are provided with a specific voltage. When the IP dimmer switch is moved from MIN to MAX, all VF displays and all incandescent back lighting respond from minimum intensity to maximum brightness in response to the IP dimmer switch.

The driver may select parade mode by manually turning on the park lamps during daylight conditions. The front park lamp circuit supplies voltage to the instrument panel cluster, the radio, and the HVAC assembly for a park lamp on input, and the displays become full bright.

Driver Controls and Modules

Driver controls include the following components:

    • The Emergency Flasher Switch
    • The Fog Lamp Switch
    • The Headlamp Dimmer Switch
    • The Headlamp Switch
    • The Interior Lamp Switch
    • The IP Dimmer Switch
    • The Stop Lamp Switch
    • The Turn Signal Switch

Three modules process the inputs and the controls. The ambient light sensor supplies the BCM with a signal for daytime conditions or for low light conditions.

    • The Ambient Light Sensor
    • The Body Control Module (BCM)
    • The Instrument Panel Cluster (IPC)

Battery Rundown Protection / Inadvertent Power

The BCM controls the lighting system through circuits that enable both the exterior lamp functions of the park lamps, the head lamps, the fog lamps, and 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 resets for another 20 minutes.