Exterior Lighting Systems

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

EXTERIOR LAMPS
The exterior lighting system consists of the following lamps:
- The headlamps
- The daytime running lamps
- The automatic headlamps and park lamps
- The fog lamps
- The park, tail and marker lamps
- The turn signal lamps
- The hazard lamps
- The stop lamps
- The backup lamps

HEADLAMPS
The headlamps may be turned ON 2 different ways. First, when the driver places the headlamp switch in the HEAD position, for normal operation. Second, with the headlamp switch placed in the AUTO position, during operation in low light conditions.

The LH HDLP and RH HDLP fuse in the fuse block - underhood, supply battery positive voltage to both low beam lamps and high beam lamps at all times. The low beam and high beam circuits continue through the fuse block - underhood , through the body control module, and to the headlamp switch. The low beam or high beam circuit then, depending on the position of the dimmer switch, continues to the headlamp switch. When the headlamp switch is placed in the ON position, it provides a ground path for the low beam or high beam lamps through G203. The low beam and high beam circuits are monitored by the BCM.

During automatic headlamp operation in low light conditions the BCM will apply voltage to the coil side of the headlamp relay, energizing it. When the headlamp relay energizes, it provides a ground path for the low beam or high beam lamps through G203, depending on the dimmer switch position.

DAYTIME RUNNING LAMPS (DRL)
The front turn signal lamps are used as both daytime running lamps (DRL) and turn signals lamps. The body control module (BCM) illuminates the front turn signals lamps in a non flashing mode for DRL operation. If the turn signal switch is activated during DRL operation, the appropriate turn signal will flash.

The DRL are designed to be automatically illuminated when the ignition is ON and the outside (ambient) light level is high as in daytime conditions (day mode). The DRL will not operate if the ambient light levels are too low (night mode). Light levels are detected by the ambient light sensor, a light sensitive transistor that varies its voltage signal to the BCM in response to changes to the ambient light level. When the BCM receives a day mode signal from the ambient light sensor it will then illuminate the DRL lamps. The automatic headlamps and park lamps will not operate when the DRL lamps are on.

In the day mode, the ambient light sensor detects daylight and the BCM applies voltage to the LH and RH front turn signal lamps illuminating the lamps under the following conditions:
- The ignition switch is in the RUN position.
- The headlamps are OFF.
- The park brake is OFF (released).
- The RH or LH turn signal is OFF.

AUTOMATIC HEADLAMPS AND PARK LAMPS
The automatic headlamps and park lamps are designed to automatically illuminate when the ignition is ON and the outside (ambient) light level is low as in night time conditions (night mode). Light levels are detected by the ambient light sensor, a light sensitive transistor that varies its voltage signal to the BCM in response to changes to the ambient light level. When the BCM receives a low light mode signal from the ambient light sensor it will then energize the park lamp and automatic headlamp relays illuminating the headlamps and park lamps. The DRL lamps will not operate when the automatic headlamps and park lamps are on.

In the low light mode, the ambient light sensor detects low light level, the BCM turns OFF the front turn signal lamps and grounds the park lamp relay and automatic headlamp relay control circuits, turning ON the headlamps and park lamps under the following conditions:
- The ignition switch is in the RUN position.
- The headlamps are OFF.
- The park brake is OFF (released).

If the engine stalls with the DRL in the low light mode, the BCM turns OFF the headlamps while the engine is being cranked. The park lamps will remain ON while the engine is being cranked.

FOG LAMPS
The FOG LP fuse in the fuse block - underhood supplies battery positive voltage to the switch side of the fog lamp relay at all times. When the fog lamp switch is pressed, it pulls the front fog lamp switch signal circuit low to the BCM. The BCM then supplies ground to the coil side of the fog lamp relay, energizing the relay. The switch side of the fog lamp relay then supplies voltage to both front fog lamps. The front fog lamps are connected to ground at G101. The park lamps or headlamps must be ON for the fog lamps to operate.

PARK, TAIL AND MARKER LAMPS
The park, tail and marker lamps, including the license lamps, are illuminated when the headlamp switch is placed in the PARK or HEAD position. The PARK fuse in the BCM supplies battery positive voltage to the headlamp switch. When the headlamp switch is placed in the PARK or HEAD position, the headlamp switch supplies voltage to the park lamp supply voltage circuit. The park lamp supply voltage circuit goes from the headlamp switch, to the BCM, and then to the park, tail and marker lamps. The park, tail, and marker lamps receive a ground at G101, G401, or G403.

TURN SIGNAL LAMPS
The HAZARD fuse in the fuse block - I/P provides battery positive voltage to the flasher module. The TURN fuse in the fuse block - I/P provides ignition positive voltage to the flasher module. The turn signal lamps may only be activated with the ignition switch in the ON position. When the turn signal switch is placed in either the left or right position, current flow is from the flasher module output to the turn signal switch assembly. The 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 activated, all the turn signal lamps will flash including both IPC turn signal indicators.

HAZARD LAMPS
When the hazard switch is activated, it pulls the turn/hazard request circuit low. The BCM then provides an ON - OFF voltage to all of the turn signal lamps and both turn signal indicators. The turn signals receive a ground at G101, G401, or G403.

STOP LAMPS
The 15A BRAKE fuse located in the fuse block - underhood, supplies battery positive voltage to the normally open stop lamp switch. When the driver presses the brake pedal, the switch contacts close and battery positive voltage is supplied to both left and right stop lamp assemblies and the center high mounted stop lamp (CHMSL), through the BCM. The stop lamps are grounded at G401 and G403. The CHMSL is grounded at G301.

BACKUP LAMPS
The 10A BACKUP fuse in the fuse block - underhood supplies ignition positive voltage to the park/neutral position (PNP) switch of an automatic transmission or the backup lamp switch of a manual transmission. When the transmission is placed in reverse, the appropriate switch supplies voltage to the back up lamps. The back up lamps receive ground at G401 and G403.