GM Service Manual Online
For 1990-2009 cars only

Exterior Lamps

The exterior lighting consist of the following lamps:

    • Headlamps
    • Daytime Running Lamps (DRL)
    • Fog Lamps
    • Park, Tail, Licence and Marker Lamps
    • Turn Signal/Hazard Lamps
    • Stop Lamps
    • Backup Lamps

Headlamps

The headlamps may be turned on in three different ways.

    • When the headlamp switch is placed in the ON position, for normal operation.
    • With the headlamp switch placed in the AUTO position, for automatic lamp control (ALC)
    • With the headlamp switch placed in the AUTO 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 dash integration module (DIM) provides battery positive voltage to the signal circuits of the headlamp switch. The signal circuits include the headlamp switch headlamps on signal and the flash to pass switch signal circuit.

With the headlamp switch in the ON position, a ground path is available for the headlamp switch signal circuit of the DIM through the headlamp switch. The DIM provides ground to either the headlamp low beam relay control circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay control circuit has ground. The DIM supplies battery positive voltage to the relay control circuits, if the headlamps are necessary. The fuse block - underhood supplies battery positive voltage to both relay switch circuits. When the headlamp low beam relay control circuit is energized, current flow is to both low beam fuses and to the low beam headlamps. The headlamps have ground at G103 and at G401. When the headlamp high beam relay control circuit is energized, current flow is to both high beam fuses and to the high beam headlamps. The high beam circuit is divided into a left and right side circuit. 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 the normally-closed contact of the DRL relay to G103. 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 G401. When the headlamp dimmer switch lever is pulled toward the driver, the flash-to-pass switch closes. This grounds the DIM flash to pass switch signal. In response to this signal, the DIM energizes the HDLP HI BM relay. Both high beams remain on until the driver releases the switch handle. If the low beam headlamps were on during a Flash-to-Pass operation, the low beams remain on. The headlights may be switched to high beam with the opposite movement of the headlamp dimmer switch lever.

Daytime Running Lamps (DRL)

Twilight sentinel is a driver convenience that controls the exterior lamps in response to changes to the outside, ambient light level. The sunload sensor assembly is a light sensitive photocell that varies its voltage signal to the instrument panel integration module (IPM) in response to changes to the outside, ambient light level. When the IPM receives this signal, the IPM sends a class 2 message to the dash integration module (DIM) and to the rear integration module (RIM). When the headlamp switch is in AUTO, the DIM 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. The FOG/DRL fuse in the fuse block - underhood supplies battery positive voltage to the switch circuit of the DRL relay. Battery positive voltage is also supplied to the DRL relay control circuit from the fuse block - underhood which is energized by the DIM. When the DIM energizes the DRL relay control circuit, the current flows from the switch contacts of the DRL relay 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 G401. The high beam headlamps are now 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 sunload sensor assembly indicates daytime conditions, the DRL will illuminate.

Front/Rear Fog Lamps

With the ignition switch in the ON position and the park lamps or low beam headlights on, the fog lights will illuminate when the driver moves the front fog lamp switch to the ON position. The fuse block - underhood supplies battery positive voltage to the switch circuit of the FOG LP relay. Ignition voltage is available to the fog lamp relay control circuit. The dash integration module (DIM) controls the fog lamp relay control circuit. When the front fog lamp switch is ON, the front fog lamp switch signal of the instrument panel integration module (IPM) has ground. The IPM sends a class 2 message to the DIM, which energizes the fog lamp control circuit of the FOG LP relay located in the fuse block - underhood. When the DIM energizes the FOG LP relay, the current flows from the FOG LP relay switch to both front fog lamps. The front fog lamps have ground at G401. The state of the front fog lamps, on or off will remain the same until the front fog lamp switch is moved to the OFF position, even between ignition cycles. The park lamps or low beam headlights must be ON in order for the fog lights to be illuminated. Fog lamp operation will be cancelled whenever the park lamps are turned OFF or the high beam headlights have been selected.

The rear fog lamps are controlled in much the same way, however the front fog lamps must be on in order to turn on the rear fog lamps. The rear fog lamps have there own RR FOG LP relay located in the fuse - block rear, and both the relay control and current flow are the same.

Park, Tail, License and Marker Lamps

The park lamps, including the license lamps, are turned on when the headlamp switch is placed in the PARK or ON position or anytime the headlights are requested. The park lamps are also turned on with the front fog lights. The fuse block - rear supplies battery positive voltage to the switch contacts of the PRK LP relay. When the headlamp switch is in PARK or in ON, the park lamp switch on signal circuit of the dash integration module (DIM) has a ground path. The DIM provides battery positive voltage to the park lamp relay control circuit of the PRK LP relay. When the park lamps and/or the tail lamps are ON, the DIM energizes the park lamp relay control circuit. This closes the switch contacts. Current flows from the PRK LP relay to the LP PK L fuse and to the LP PK R fuse. From the fuse, the current flows to the park lamps. The left park lamps are grounded at G103 and G402. The right park lamps and the right tail lamps are grounded at G401. When the park lamps are activated the PRK LP relay supplies battery positive voltage through the DIMR fuse to the license lamps and to the instrument panel lamp fuse supply voltage - 1 circuit of the DIM, for interior lamps dimming. The license lamps are grounded at G401.

Remote Keyless Entry Exterior Lamp Illumination

When the remote control door lock receiver (RCDLR) receives a door UNLOCK command from the keyless entry transmitter, the RCDLR will send a class 2 message to the dash integration module (DIM). The DIM inputs must indicate that the ignition switch is OFF, all the doors are closed and the sunload sensor assembly is indicating low light conditions. The DIM will then activate the headlamps and park lamps. The DIM will flash the headlamps and park lamps twice, then keep them on approximately 25 seconds or until a door is opened. When the RCDLR receives a door LOCK command from the keyless entry transmitter, The DIM will flash the headlights and park lights once. In daylight conditions, the DIM will activate the park lamps only to flash the park lamps twice with a door UNLOCK command and once with a door LOCK command from the keyless entry transmitter.

Turn Signal/Hazard Lamps

The T/SIG HAZ fuse in the fuse block - rear supplies battery positive voltage to the turn signal/hazard flasher module. The turn signal/hazard flasher module has ground at G201. The turn signal lamps may only be activated with the ignition switch in the ON or ACCY position. The IGN-1 fuse in the fuse block - rear 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 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 panel 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 G103 and at G402. The right turn signals have ground at G103 and G401.

Stop Lamp

The STOP LP fuse in the fuse block - rear 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 stop lamp and the CHMSL have ground at G402. The right stop lamp has ground at G401.

Backup Lamps

The fuse block - rear supplies battery positive voltage to the control circuit and to the switch terminals of the REVERSE relay. Battery positive voltage to the switch terminal is available through the PARK/REV fuse. The dash integration module (DIM) sends a power mode message to the rear integration module (RIM) indicating that the ignition is in the ON position. When the driver selects the REVERSE position, the powertrain control module (PCM) sends a class 2 message to the RIM. The message indicates that the gear selector lever is in the REVERSE position. The RIM then energizes the REVERSE relay and the backup lamps illuminate. Current flows from the REVERSE relay switch to the backup lamps. The backup lamps have ground at G401 and G402.

Lighting System Indicators

    • Fog Lamp
        The instrument panel cluster (IPC) illuminates the fog lamp indicator when any of the following occur:
      • The instrument panel module (IPM) detects that the fog lamps are requested. The IPC receives a class 2 message from the IPM requesting illumination.
      • The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 5 seconds.
    • HEADLAMPS SUGGESTED -- 27
        The DIC displays the HEADLAMPS SUGGESTED -- 27 message when the DIM determines that the ambient light conditions require headlamp illumination. The IPC sends a class 2 message to the radio in order to activate an audible warning.
    • High Beam
        The IPC illuminates the high beam indicator when the dash integration module (DIM) detects that the high beams are requested. The IPC receives a class 2 message from the DIM requesting illumination.
    • TURN SIGNAL ON? -- 24
        The DIC displays the TURN SIGNAL ON? -- 24 message when the IPC determines that the turn signal is active for more than 1.29 km (0.8 mi). The IPC sends a class  2 message to the radio in order to activate the audible warning.
    • Turn Signals
        The IPC illuminates the right or left turn signal indicator when the IPC detects a turn signal request or a hazard request. If the IPC determines that the turn signal is active for more than 1.29 km (0.8 mi), the IPC sends a class  2 message to the radio in order to activate the audible warning.

Battery Run Down Protection/Inadvertent Power

To provide battery run down protection, the exterior lamps will be deactivated automatically under certain conditions. The dash integration module (DIM) monitors the state of the headlamp switch. If the park or headlamp switch is ON when the ignition switch is placed in either the CRANK or RUN position and then placed in the OFF position, the DIM initiates a 10 minute timer. At the end of the 10 minutes, the DIM will turn off the control power output to the park and headlamp relay coils, deactivating the exterior lamps. This feature will be cancelled if any power mode other than OFF becomes active. The DIM will disable battery run down protection if any of the following conditions exist. The park or headlamp switch is placed in the ON to OFF position and back to the ON position during battery run down protection. The DIM determined that the park or headlamp switch was not active when the ignition was turned OFF.