Headlamps
Battery voltage is applied constantly to the headlamps through two fuse.
The DRL/EXT LAMPS fuse for the left side headlamp and the EXT LAMPS fuse for
the right side headlamp. When the headlamp switch is turned to the HEAD
position, ground is applied through the headlamp switch to the BCM using
the headlamp switch output circuit. When the BCM receives the headlamp switch
output signal, it applies a ground to the headlamp relay coil control circuit.
When a ground is applied to the headlamp relay coil control circuit this
engages the headlamp relay, closing the switch contacts and applies a ground
through the headlamp relay to the headlamp relay contact circuit to the
headlamp dimmer switch. Depending on the headlamp dimmer switch position
the ground circuit would then be applied to either the high beam headlamps
or the low beam headlamp turning them on.
Daytime Running Lamps (DRL)
The Daytime Running Lamps (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.
The DRL are designed to automatically operate exterior lights depending
on outside light conditions.
The DRL operates in 2 modes:
| | In the day mode, the BCM turns ON the high beam headlamps at a reduced
intensity when the headlamp auto control ambient light sensor detects daylight
under the following conditions: |
| - | The ignition switch is in the RUN position. |
| - | The park brake is OFF (released). |
| | In the low light mode, the headlamp auto control ambient light sensor
detects darkness, turning OFF the high beam headlamps and turning ON the low
beam headlamps. |
| | Additionally, the headlamp auto control ambient light sensor turns ON
the following lamps: |
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 BCM turns ON the
following lamps:
The following lamps operate in the usual manner:
| • | The instrument panel lamp dimmer switch. |
B+ is applied constantly to both the coil and switch side of the DRL
Relay:
| • | In Day Mode: The BCM applies a ground to the DRL Relay coil control
circuit to the DRL relay. This energizes the relay and allows B+ to be applied
through the high beam DRL feed circuit to the high beam headlamps in series.
This illuminates the high beam headlamp at reduced intensity |
| • | In Low Light Mode: the BCM removes the ground from the DRL relay
coil circuit. This disengages the DRL relay and allows B+ to be applied directly
to the high beam headlamp allowing them to be controlled by the headlamp
dimmer switch. The BCM then applies a ground to the headlamp relay coil
control circuit and turns the headlamps on through the same headlamp control
circuit as normal headlamp switch operation. |
Headlamp Auto Control Ambient Light Sensor
The DRL ambient light sensor is a light sensitive variable resistor.
The headlamp auto control ambient light sensor's resistance decreases as the
outside light intensity increases. Measuring the voltage drop across the
DRL ambient light sensor and determining whether it should operate in the
day mode or in the low light mode are the 2 basic features of the
headlamp auto control ambient light sensor.
Park Brake Input
The BCM will not operate any headlamps or exterior lamps, if the park
brake is applied before the ignition switch is turned to the RUN position.
This allows the driver to start the vehicle and keep the headlamps OFF,
as long as the park brake is applied. The BCM will activate the headlamps
when the park brake is released with the ignition switch in the RUN position.
This feature functions only when the park brake is applied before the ignition
switch is turned to the RUN position. The headlamps will turn OFF, if the
park brake is applied after the ignition switch is turned to the RUN position.
Special Equipment Option (SEO)
If the emergency vehicle interior lamp switch is turned to the ON position,
the DRL lamps and the instrument cluster are turned OFF. This enables the
vehicle to have the engine running with all of the exterior and interior
lights OFF. The headlamps and other exterior lamps are still controlled
by the headlamp switch.
