2-40 Lighting
Description and Operation
Exterior Lighting Systems
Description and Operation
The exterior lighting system consist of the following
lamps:
• Backup lamps
• Cargo lamps
• Daytime running lamps (DRL)
• Exterior courtesy lamps
• Hazard warning lamps
• Headlamps
• Park, tail, license, and marker lamps
• Front fog lamps (T3U)
• Stop lamps
• Task lamps
• Turn signal lamps
• Trailer lighting, refer to
Trailering Description and
Operation on page 2‑59 for more information.
Low Beam Headlamps
The headlamps may be turned ON in 3 different ways:
• When the headlamp switch is placed in the ON
position, for normal operation
• When the headlamp switch is placed in the AUTO
position, for automatic lamp control during low
ambient light conditions
• When the headlamp switch is placed in the AUTO
position, with the windshield wipers ON in daylight
conditions, after a 6 second delay
The K9 Body Control Module (BCM) monitors three
signal circuits from the S30 Headlamp Switch. When
the headlamp switch is in the AUTO position, the three
signal circuits are unaffected (open) and the BCM relies
on the B10D Sun Load and Ambient Light and Security
Indicator Sensor input to determine if headlamps are
required or if daytime running lamps will be activated
based on outside lighting conditions. When the
headlamp switch is placed in the headlamp OFF
position, the headlamp switch headlamps OFF signal
circuit is grounded, indicating to the BCM that the
exterior lamps should be turned OFF. With the
headlamp switch in the PARK LAMPS position, the
headlamp switch park lamps ON signal circuit is
grounded, indicating that the park lamps have been
requested. When the headlamp switch is in the
HEADLAMP position, both the headlamp switch park
lamps ON signal circuit and the headlamps ON signal
circuit are grounded. The BCM responds to these
inputs by sending a serial data message to the
K219 Lighting Control Module. The Lighting Control
Module responds by applying pulse width modulated
(PWM) voltage to both headlamp low beam control
circuits, illuminating the low beam headlamps. When
the Lighting Control Module commands the low beam
headlamps ON, the operator will notice the interior
backlighting for the instrument cluster and the various
other switches dim to the level of brightness selected
by the instrument panel dimmer switch.
High Beam Headlamps
The high beam and flash to pass (FTP) functions are
contained within the S78 Turn Signal Switch. The
K9 Body Control Module (BCM) provides the turn
signal/multifunction switch with two signal circuits, the
high beam signal circuit and the FTP signal circuit.
When the low beam headlamps are ON, and the turn
signal/multifunction switch is placed in either the high
beam position or FTP position, ground is applied to the
BCM through the high beam/FTP signal circuit. The
BCM responds to the high beam request by sending a
serial data message to the K219 Lighting Control
Module. The Lighting Control Module responds by
applying pulse width modulated (PWM) voltage to both
headlamp high beam control circuits, illuminating the
high beam headlamps. The status of the high beam
lamps is shown by a blue indicator located on the
instrument cluster. When high beams are commanded
on, the indicator will be illuminated continuously. If the
driver turns the high beams off, the indicator will also
turn off.
Flash to Pass
When the S78 Turn Signal Switch is momentari ly
placed in the flash to pass position, ground is applied to
the turn signal/multif unction switch. The turn signal/
multifunction switch applies ground to the K9 Body
Control Module (BCM) through the flash to pass switch
signal circuit. The BCM responds to the flash to pass
request by sending a serial data message to the
K219 Lighting Control Module. The Lighting Control
Module responds by applying pulse width modulated
(PWM) voltage to both headlamp high beam control
circuits, illuminating the high beam headlamps. This
causes the high beam headlamps to illuminate at full
brightness until the turn signal/multifuncti on switch is
returned to the at rest position.
Automatic Headlamp Control
The K9 Body Control Module (BCM) monitors three
signal circuits from the S30 Headlamp Switch. When
the headlamp switch is in the AUTO position, the three
signal circuits are unaffected (open) and the BCM relies
on the B10D Sun Load and Ambient Light and Security
Indicator Sensor input to determine if headlamps are
required or if daytime running lamps will be activated
based on outside lighting conditions. During automatic
lamp control, the headlamps will be off during daylight
conditions but will turn on when the ambient light
sensor detects low ambient light conditions. The
ambient light sensor is a light sensitive transistor that
varies the voltage signal to the BCM. The BCM
provides a 5 volt reference signal and a low reference
ground to the ambient light sensor. During low light
conditions the BCM will request the low beam
headlamps ON by sending a serial data message to the
K219 Lighting Control Module. The Lighting Control
Module responds by applying pulse width modulated
(PWM) voltage to both headlamp low beam control
circuits, illuminating the low beam headlamps.
Intellibeam – Automatic High Beam
Assist (TQ5)
The IntelliBeam system is activated by pressing the
auto high beam assist button on the turn signal switch
while the exterior lamp control is in AUTO mode and
2022 - Silverado 1500 (New) Electrical Body Builder Manual
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