Low Beam Headlamp Operation
The headlamps may be turned ON in 3 different ways:
• When the headlamp switch in the HEAD position
for normal operations
• When the headlamp switch is in the AUTO
position, for automatic lamp control (ALC)
• When the headlamp switch is placed in the AUTO
position, with the windshield wipers ON in daylight
conditions, after a 6 second delay
Battery voltage is applied at all times to the coil and
switch sides of the LOW BEAM PCB Relay located in
the underhood fuse block. With the headlamp switch in
the headlamps ON position, ground is applied through
the headlamps ON switch signal circuit to the body
control module (BCM) signaling the headlamps ON
request. In response to this signal, the BCM applies
ground through the low beam relay control circuit
energizing the LOW BEAM PCB Relay. With the relay
energized, battery voltage is applied through the switch
side of the relay, the LT and RT LOW BEAM fuses, and
the low beam supply voltage circuits illuminating the
low beam headlamps.
High Beam Headlamp Operation
Battery voltage is applied at all times to the coil and
switch sides of the HIGH BEAM PCB Relay located in
the underhood fuse block. When the headlamp dimmer
switch is placed in the high beam position, the
headlamp dimmer switch signal circuit to the BCM is
pulled low signaling the headlamp high beam request.
In response to this signal, the BCM applies ground
through the high beam relay control circuit energizing
the high beam relay. With the relay energized, battery
voltage is applied through the switch side of the relay,
the LT and RT HIGH BEAM fuses, and the high beam
supply voltage circuits illuminating the high beam
headlamps. At the same time the BCM sends a serial
data message to the instrument panel cluster (IPC)
requesting the IPC to illuminate the high beam
indicator.
Flash to Pass (FTP)
When the headlamp dimmer switch is pulled toward the
driver, the flash to pass signal circuit to the BCM is
pulled low signaling the flash to pass request. The BCM
then turns ON the high beam headlamps as described
above until the headlamp dimmer switch is released.
If the low beam headlamps were ON during FTP
operation they will remain ON.
Daytime Running Lamps (DRL) and
Automatic Lamp Control (ALC)
The low beam headlamps are used for DRL operation
at a reduced intensity. The DRLs will operate only with
the ignition ON, the headlamp switch in the AUTO
position, and the gear selector out of the park position.
No other exterior lamps such as the parking lamps, tail
lamps, etc. will be on when the DRL are being used.
The instrument panel will not be illuminated either.
DRL operation is determined by the ambient light
sensor and controlled by the body control module
(BCM). The ambient light sensor is a light-sensitive
transistor used to monitor outside lighting conditions.
The BCM provides a 5-volt reference signal to the
sensor. The sensor will vary this voltage signal between
0.2 and 4.9 volts depending on outside lighting
conditions. The BCM monitors the ambient light sensor
signal circuit to determine if outside lighting conditions
are correct for either DRL or ALC operation. When the
BCM determines the conditions are met for DRL
operation, it applies ground to the DRL relay control
circuit energizing the DRL PCB Relay. With the relay
energized, battery voltage is applied through the switch
side of the relay, the DRL 1 fuse, the DRL 2 fuse, both
low beam headlamp fuses, and the low beam supply
voltage circuits illuminating the headlamps at a reduced
intensity. Any function or condition that turns on the
headlamps will cancel DRL operation.
When the BCM detects low light conditions, it will turn
OFF the daytime running lamps and turn ON the low
beam headlamps as described above in Low Beam
Headlamp Operation. The BCM will also turn ON the
low beam headlamps in daylight conditions when the
windshield wipers are turned ON.
HDLPS Suggested Indicator
If the park lamps are turned ON manually and the
ambient light sensor detects a low light condition then
the body control module (BCM) will send a message to
the instrument panel cluster (IPC) to display the
HEADLAMPS SUGGESTED message.
