GM Service Manual Online
For 1990-2009 cars only

Interior Lamps

The interior lighting consist of the following 2 groups. This first group includes lamps that may not be dimmed.

    • Courtesy/illuminated entry lamps
    • Dome lamps
    • Reading lamps
    • Vanity mirror lamps

Courtesy/Illuminated Entry Lamps (Without YF7)

The courtesy/illuminated entry lamps, may be manually turned on or off by placing the interior lamp switch in the ON or OFF position. If a door is opened, the courtesy/illuminated entry lamps illuminate. After all the doors have been closed the courtesy/illuminated entry lamps will remain illuminated approximately 15 seconds. The courtesy/illuminated entry lamps will also turn on prior to any door being opened, and remain illuminated approximately 40 seconds when the driver removes the ignition key. If the interior lamp switch is turned on when the ignition key is OFF, or the interior lamp switch is left on when the ignition key is turned OFF the BCM will turn off the courtesy lamps after approximately 10 minutes.

When the driver places the dome lamp defeat switch in the OFF position, the courtesy/illuminated entry lamps will be disabled, however will still operate from the interior lamp switch.

The courtesy lamps are controlled and receive voltage from the BCM. The BCM receives signals from the mini wedges and door jamb switches when a door is opened or anytime the courtesy lamp on switch is placed in the ON position. Ground is provided to the cargo mini wedge at G402. Ground is provided to the remaining switches as well as all courtesy, reading and vanity lamps at G347.

Voltage for the courtesy lamp supply voltage and the backup lamp supply voltage circuits is from the TBC 2 fuse 18 in the underhood fuse block directly through the BCM to these circuits.

Courtesy/Illuminated Entry Lamps (With YF7)

The courtesy/illuminated entry lamps operate the same as above, however, the circuit functionality is different as follows:

The CTSY LP/SEO 15A fuse in the body fuse block supplies battery positive voltage to the courtesy lamp relay switch input contacts. Ground is supplied to the courtesy lamp relay coil contact. The BCM supplies voltage on the courtesy lamp high control circuit to energize the courtesy lamp relay and supply voltage to the courtesy lamps. The BCM receives signals from the mini wedges and door jamb switches any time a door is opened, and anytime the courtesy lamp on switch is placed in the ON position. Ground is provided to the cargo mini wedge at G402. Ground is provided to the remaining switches as well as the stepwell lamps at G347.

Voltage for the courtesy lamp high control and the backup lamp supply voltage circuits is from the TBC 2 fuse 18 in the underhood fuse block directly through the BCM to these circuits.

Keyless Entry Interior Illumination

When the driver uses the door key in order to unlock the doors, the body control module (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, approximately 15 seconds after the door is closed. 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, trunk or presses the panic button, the BCM will keep the courtesy lamps on approximately 40 seconds. When the driver uses the remote function actuator transmitter to lock the doors, the BCM will keep the courtesy lamps on approximately 2 seconds. If the ignition switch is turned to either the RUN or CRANK position the courtesy lamps will turn off immediately. The BCM will also keep the courtesy lamps on approximately 40 seconds, after an alarm event is completed.

Vanity Lamps

The inadvertent supply voltage circuit of the BCM provides battery positive voltage to each vanity mirror lamp. When the vanity mirror cover on the sunshade is opened, a switch closes to provide a ground circuit and the vanity lamp illuminates. In the event that any of these lamps were to remain illuminated for a period of more than 10 minutes with the ignition switch in the OFF position, the BCM will deactivate the inadvertent power supply voltage circuit to prevent a total battery discharge condition. Ground is provided to the vanity lamps at G347.

Voltage for the inadvertent supply voltage circuit is from the TBC 4 fuse 11 in the underhood fuse block directly through the BCM to this circuit.

Reading Lamps

The inadvertent power supply voltage circuit of the BCM provides battery positive voltage to the reading lamps. The reading lamps and switch are integral to the courtesy/reading lamp assembly. When the switch is closed, voltage is supplied and the lamp illuminates. In the event that any of these lamps were to remain illuminated for a period of more than 10 minutes with the ignition switch in the OFF position, the BCM will deactivate the inadvertent power supply voltage circuit to prevent a total battery discharge condition. Ground is provided to the reading lamps at G347.

Voltage for the inadvertent supply voltage circuit is from the TBC 4 fuse 11 in the underhood fuse block directly through the BCM to this circuit.

Underhood Lamp

The inadvertent supply voltage circuit of the BCM provides battery positive voltage to the underhood lamp. When the hood is opened, a switch integral to the lamp closes to provide a ground circuit and the lamp illuminates. Ground is provided to the lamp at G347.

Voltage for the inadvertent supply voltage circuit is from the TBC 4 fuse 11 in the underhood fuse block directly through the BCM to this circuit.

Dome Fluorescent Work Lamps

Dome Fluorescent Work Lamps Components

The dome fluorescent work lamps system consists of the following components:

    • The body control module (BCM) -- Class 2 module that requires programming when replaced
    • The AUXILIARY 1 Fuse 32 50A -- Located in the body fuse block and is hot at all times
    • The DOME FLUORESCENT WORK LAMPS fuse 2 10A fuse -- Located in the rear fuse block and is hot at all times
    • The Dome Fluorescent Work Lamp Relay -- Located below the rear fuse block
    • The dome fluorescent work lamps - With on/off switches integrated into each lamp assembly

Dome Fluorescent Work Lamps Controls

Each dome fluorescent work lamps is equipped with an integral ON/OFF switch. The work lamps will remain on until manually turned off as long as the key is in the RUN position. The work lamps will also remain on for approximately 10 minutes after the ignition key has been turned to the OFF or ACCY positions. If the work lamp is turned ON with the ignition switch either in the OFF or ACCY positions, within 2 minutes after a 10 minute time out, the work lamp will turn on and remain on until the battery fully discharges.

Dome Fluorescent Work Lamps Operation

Voltage is supplied to the relay switch and coil side from the dome fluorescent work lamp10 A fuse 2 in the rear fuse block. When the work lamp on switch is pressed the BCM senses this signal on the dome fluorescent work lamp signal circuit. The BCM responds to this signal by grounding the dome fluorescent work lamp relay control circuit, energizing the relay. The relay in turn supplies voltage to the work lamps. The BCM utilizes the dome fluorescent work lamps signal circuit as a request signal when the key is in the any position except START. The work lamps are grounded at G403.

Battery Rundown Protection/Inadvertent Power

The BCM inadvertent power supply voltage circuit provides battery positive voltage to all of the interior reading lamps, underhood lamp, and both visor vanity mirror lamps. In the event that any of these lamps were to remain illuminated for a period of more than 10 minutes with the ignition switch in the OFF position, the BCM will deactivate the inadvertent power supply voltage circuit to prevent a total battery discharge condition.

The BCM also utilizes the inadvertent power supply voltage circuit as a lamp request signal circuit when the ignition key is in the OFF position. When a lamp switch is activated, the BCM receives the request for lamp illumination and switches to supplying voltage to the inadvertent power supply voltage circuit.

Interior Lamps Dimming

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

When the ignition switch is turned to the RUN position, the radio's VF displays turn on at maximum brightness. When the park lamps are on, all incandescent back lighting turn on at the dimming level indicated by the instrument panel (I/P) dimmer switch. At the same time all VF displays dim to match the indicated dimming level. The panel dimmer switch potentiometer is an input to the BCM. When the driver selects a dimming setting by moving the I/P dimming switch potentiometer, all incandescent back lighting lamps are provided with a specific voltage. When the I/P dimmer switch is moved from MIN to MAX, all VF displays, as well as all incandescent back lighting respond from minimum intensity to maximum brightness in response to the I/P dimmer switch.

The following switches and components have dimmable back lighting:

    • The traction control switch
    • The instrument panel cluster (IPC)
    • The radio controls
    • The headlamp and panel dimmer switch
    • The HVAC control assemblies
    • The inflatable restraint disable switch
    • The tow/haul switch
    • The window and door lock switches
    • The rear heater switch
    • The rear seat audio control

The I/P cluster illumination lamps, various switches and control assemblies receive voltage and are controlled by the BCM on the instrument panel lamps dimming control circuit and the backlight lamps control circuit.

Voltage for the LED dimming signal, instrument panel lamps dimming control, as well as the backlight lamps control circuits is from the TBC 3 fuse 16 in the underhood fuse block directly through the BCM to these circuits.