Exterior Lighting Systems Description and Operation

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.

On vehicles with manual headlamps, 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 (BCM), and to the headlamp switch. The low beam or high beam circuit then, depending on the position of the dimmer switch, continues through 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.

On vehicles with automatic headlamps, 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 BCM, and to the headlamp switch. The low beam or high beam circuit then, depending on the position of the dimmer switch, continues through the headlamp switch. 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.

On vehicles with automatic headlamps, 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 transaxle is not in park.
* The RH or LH turn signal is OFF.

On vehicles with manual headlamps, the DRL are designed to be illuminated when the ignition is ON and the headlamps are OFF.

When the headlamps are OFF, 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 transaxle is not in park.
* 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 body control module (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 daytime running lamps (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 fuse in the fuse block - underhood supplies battery positive voltage to the switch side of the fog lamp relay at all times. The coil side of the fog lamp relay is grounded at G101. When the fog lamp switch is pressed, it pulls the front fog lamp switch signal circuit low to the body control module (BCM). The BCM then supplies voltage 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 body control module (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

When the turn signal switch is place in either the right or left turn position, the turn/hazard request circuit is pulled low, through a resistor. The body control module (BCM) uses the resistors to determine if the left or right turn signals have been requested. The BCM then supplies an ON-OFF voltage to the turn signal lamps and turn signal indicator on the selected side of the vehicle. The turn signals receive a ground at G101, G401, or G403.

Hazard Lamps

When the hazard switch is activated, it pulls the turn/hazard request circuit low. The body control module (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 15-amp STOP fuse located in the body control module (BCM) 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.

Backup Lamps

The 15-amp BACK UP 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 backup lamps. The backup lamps receive ground at G401 and G403.