Buick Regal: Exterior Lighting Systems Description and Operation

Exterior Lamps

The exterior lighting system consist of the following lamps:

• Adaptive forward lighting
• Automatic headlamp leveling
• Automatic high beam assist
• Backup lamps
• Daytime running lamps
• Exterior courtesy lamps
• Front fog lamps
• Hazard warning lamps
• Headlamps
• Park, tail, license and marker lamps
• Stop lamps
• Turn signal lamps

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
• When the headlamp switch is placed in the AUTO position, with the windshield wipers ON in daylight conditions, after a 6 second delay

The BCM will also command the low beam headlamps ON during daylight conditions when the following conditions are met:

• Headlamp switch in the AUTO position
• Windshield wipers ON
• Vehicle in any gear but PARK

When the BCM 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.

Low Beam Headlamps - (with T4A)

The body control module (BCM) monitors three signal circuits from the headlamp switch. When the headlamp switch is in the AUTO position, all three signal circuits are open. When placed in the AUTO position, the BCM monitors inputs from the ambient light sensor 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 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 position, the headlamp switch park lamps ON signal circuit is grounded, indicating that the park lamps have been requested. When the headlamp switch is placed in the HEADLAMP position, both the headlamp switch park lamps ON signal circuit and the headlamp switch headlamps ON signal circuit are grounded. The BCM responds to the inputs by illuminating the park lamps and headlamps. When the low beam headlamps are requested, the BCM applies B+ to both low beam headlamp control circuits illuminating the low beam headlamps.

Low Beam Headlamps - (with T4L)

The body control module (BCM) monitors three signal circuits from the headlamp switch. When the headlamp switch is in the AUTO position, all three signal circuits are open. When placed in the AUTO position, the BCM monitors inputs from the ambient light sensor 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 OFF position, the headlamps OFF signal circuit is grounded, indicating to the BCM that the exterior lamps should be turned OFF. With the headlamp switch is in the PARK position, the park lamps ON signal circuit is grounded, indicating that the park lamps have been requested. When the headlamp switch is placed in the HEADLAMP position, both the park lamps ON signal circuit and the headlamps ON signal circuit are grounded. The BCM responds to the low beam request by applying ground to the low beam relay control circuit which energizes the low beam relay. With the low beam relay energized, the switch contacts close allowing battery voltage to flow through the low beam fuses.

Battery voltage is then applied from the fuses, through the low beam control circuits to the left and right headlamp/cornering lamp control modules. The left and right headlamp/cornering lamp control modules respond by illuminating there respective low beam LEDs.

High Beam Headlamps (with T4A)

When the low beam headlamps are ON and the turn signal/multifunction switch is placed in the high beam position, ground is applied to the BCM through the high beam signal circuit. The BCM responds to the high beam request by applying ground to the headlamp high beam relay control circuit which energizes the headlamp high beam relay. With the headlamp high beam relay energized, the switch contacts close allowing battery voltage to flow through the left and right high beam fuses to the high beam control circuits illuminating the left and right high beam headlamps.

High Beam Headlamps (with T4L)

When the low beam headlamps are ON and the turn signal/multifunction switch is placed in the high beam position, ground is applied to the BCM through the high beam signal circuit. The BCM responds to the high beam request by sending a message via serial data to the headlamp control module. The headlamp control module responds to the high beam request by sending a serial data message to the left and right headlamp/cornering lamp control modules located in each headlamp assembly. The left and right headlamp/cornering lamp control modules respond by illuminating their respective high beam LEDs.

Automatic Lamp Control

Automatic Light is switched ON as default. It can be switched off by turning the light switch to OFF position. It will be switched ON again by doing so again. Automatic Light is only available if a rain sensor or rain/light sensor module (RSM) in installed in the car. RSM will send the actual ambient light state (day/night) to the BCM. If Automatic Light is enabled, BCM will react on the message received from RSM by switching ON/OFF low beams.

Flash to Pass (with T4A)

When the low beam headlamps are ON and the turn signal/multifunction switch is momentarily placed in the flash to pass position, ground is applied to the turn signal/multifunction switch. The turn signal/multifunction switch applies ground to the BCM through the flash to pass switch signal circuit.

The BCM then applies ground to the high beam relay control circuit. This energizes the high beam relay, closing the switch side contacts of the high beam relay, applying battery voltage to the left and right high beam fuses. Battery voltage is applied from the high beam fuses through the high beam voltage supply circuit to the high beam headlamp assemblies. This causes the high beam headlamps to illuminate at full brightness momentarily or until the flash to pass switch is released.

Flash to Pass (with T4L)

When the turn signal/multifunction switch is momentarily placed in the flash to pass position, ground is applied to the turn signal/multifunction switch. The turn signal/multifunction switch applies ground to the body control module (BCM) through the flash to pass switch signal circuit. The BCM responds to the flash to pass request by sending a message via serial data to the headlamp control module. The headlamp control module responds to the flash to pass request by sending a serial data message to the left and right headlamp/cornering lamp control modules located in each headlamp assembly. The left and right headlamp/cornering lamp control modules respond by illuminating their respective high beam LEDs momentarily or until the flash to pass switch is released.

Adaptive Forward Lighting

The adaptive forward lighting consist of the following components:

• Headlamp control module
• Headlamp/cornering lamp control module - left
• Headlamp/cornering lamp control module - right

Cornering Light

The cornering lamp is activated automatically at vehicle speeds below 40 km/h (25 MPH) when the direction indicator is switched ON and/or when the steering angle is changed from the straight-ahead position towards the side the vehicle is going to turn and passes a programmable angle threshold. The cornering lamp is deactivated automatically when the direction indicator is switched OFF and/or the steering angle has returned in the straight-ahead position. The cornering lamps are deactivated at vehicle speeds above 40 km/h (25 MPH). If reverse gear is active, the cornering lamps go into park function.

Both lamps will be switched on. They will switch off 20 seconds after leaving reverse gear or if the vehicle speed exceeds 7 km/h (4 MPH). The cornering lamps also provide a protection against overheating. When having been continuously switched on for 2 minutes, adaptive forward lighting will deactivate the lamps for 2 minutes to enable cooling down.

Town Light

Town Light is activated while the vehicle speed is below 55 km/h (34 MPH) as well as the light sensor detects street lights and the town road category is detected. The light distribution is reduced to an area near the car due to low speeds.

Motorway Light

If vehicle speed is above 115 km/h (71 MPH) for at least 40 seconds (or once above 125 km/h (78 MPH) and the corresponding road category is identified, the headlamps will be switched to a motorway light distribution. The light distribution on the left lane is reduced to minimize glare when the lanes are separated by guardrails. This improves the visibility range at the far end of the road.

Country Light

Country light replaces the current low beam and will be controlled based on programmable vehicle thresholds as well as corresponding road detection. The vehicle speed has to be between 55 km/h (34 MPH) and 100 km/h (62 MPH). Country light is the default light distribution at 35 W. Light distribution is reduced on the left side to prevent oncoming traffic from being dazzled.

Tourist Mode

The tourist mode functionality switches the adaptive forward lighting headlamps into a non dazzling mode, if the traffic regulation moves from left hand traffic to right hand traffic and vice versa. Vehicles with halogen headlights (T4A) do not have to be adjusted. Vehicles with LED headlights (T4L) can be set for driving on the opposite side of the road via the vehicle personalization menu on the info display.

Each time the ignition is switched on and the tourist mode is active, the warning indicator flashes for about 4 seconds. The warning indicator will not flash when the tourist mode function is deactivated.

Automatic Headlamp Leveling

The automatic headlamp leveling system consist of the following components:

• Headlamp control module
• Headlamp leveling control module - left
• Headlamp leveling control module - right
• Headlamp leveling actuator - left
• Headlamp leveling actuator - right
• Suspension height sensor - left front (without electronic suspension control)
• Suspension height sensor - left rear (without electronic suspension control)

Automatic Headlamp Leveling (without Electronic Suspension Control)

The automatic headlamp leveling system automatically maintains the vertical alignment of the headlamps when the vehicle load and driving conditions change. The vehicle is equipped with suspension height sensors located on the left front and left rear suspensions. Each sensor receives a 5 V reference, signal, and low reference circuits from the headlamp control module. The headlamp control module receives inputs from the front and rear suspension height sensors to determine vehicle pitch. The headlamp control module calculates the difference in vehicle pitch and sends a serial data message to both headlamp leveling control modules located in each headlamp assembly. The headlamp leveling control modules responds by driving their respective headlamp leveling actuators to the position commanded by the headlamp control module.

Automatic Headlamp Leveling (with Electronic Suspension Control)

The front and rear vertical suspension acceleration sensors provide the suspension control module with suspension position information. Each sensor receives a 5 V reference, signal, and low reference circuits from the suspension control module. The vertical suspension acceleration sensors are connected to each control arm of the front and rear suspensions. As the vehicle travels, the suspension compresses and rebounds moving the vertical suspension acceleration sensors. This causes the signal output of the sensor to change. The suspension control module compares the information from all four vertical suspension acceleration sensors and adjusts the suspension as needed. The suspension control module communicates the suspension positions with the headlamp control module via serial data. The headlamp control module uses the suspension position sensor information received from the suspension control module to calculate the difference in vehicle pitch and sends a serial data message to both headlamp leveling control modules located in each headlamp assembly. The headlamp leveling control modules responds by driving their respective headlamp leveling actuators to the position commanded by the headlamp control module.

Daytime Running Lamps

The daytime running lamps will illuminate continuously when the following conditions are met:

• The ignition is in the RUN or CRANK position
• The shift lever is out of the PARK position for vehicles equipped with automatic transmissions or the parking brake is released for vehicles with manual transmissions
• The low and high beam headlamps are OFF

Daytime Running Lamps

The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 V and 4.9 V depending on outside lighting conditions. The body control module (BCM) provides a 5 V reference signal to the ambient light sensor and the HVAC control module provides a low reference ground. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lamps or automatic lamp control when the headlamp switch is in the AUTO position. In daylight conditions the BCM will command the daytime running lamps ON. During low light conditions the BCM will command the low beam headlamps ON. Any function or condition that turns on the headlamps will cancel daytime running lamps operation.

Front Fog Lamps

The front fog lamp relay is supplied with battery voltage at all times. The front fog lamp switch signal circuit is grounded momentarily by pressing the front fog lamp switch. The body control module (BCM) energizes the front fog lamp relay by applying ground to the front fog lamp relay control circuit. When the front fog lamp relay is energized, the relay switch contacts close and battery voltage is applied through the front fog lamp fuse to the front fog lamp supply voltage circuit which illuminates the front fog lamps.

Hazard Lamps

The hazard flashers may be activated in any power mode. The hazard switch signal circuit is momentarily grounded when the hazard switch is pressed. The body control module (BCM) responds to the hazard switch signal input by supplying battery voltage to all four turn signal lamps in an ON and OFF duty cycle. When the hazard switch is activated, the BCM sends a serial data message to the instrument panel cluster requesting both turn signal indicators to be cycled ON and OFF.

The instrument panel dimmer switch controls the brightness of the interior backlighting components.

When the instrument panel dimmer switch is placed in a desired brightness position, the body control module (BCM) receives a signal from the instrument panel dimmer switch and responds by applying a pulse width modulated (PWM) voltage to the hazard switch light emitting diode (LED) backlighting control circuit illuminating the LED to the desired level of brightness.

Park, Tail, and License Lamps

When the turn signal/multifunction switch is placed in the HEAD or PARK position, ground is applied to the turn signal/multifunction switch park lamp switch ON signal circuit to the body control module (BCM). The BCM responds by applying voltage to the park lamps, tail lamps, and license lamps control circuits illuminating the park, tail, and license lamps.

Stop Lamps

The brake pedal position sensor is used to sense the action of the driver application of the brake pedal.

The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5 V reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery voltage to the stop lamps/center high mount stop lamp control circuit illuminating the left and right stop lamps and the center high mounted stop lamp.

Turn Signal Lamps

Ground is applied at all times to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START position. When the turn signal/multifunction switch is placed in either the TURN RIGHT or TURN LEFT position, ground is applied to the BCM through either the right turn or left turn signal switch signal circuit. The BCM then applies a pulsating voltage to the front and rear turn signal lamps through there respective voltage supply circuits. When a turn signal request is received by the BCM, a serial data message is sent to the instrument cluster requesting the respective turn signal indicator be pulsed ON and OFF.

Backup Lamps

With the engine ON and the transmission in the REVERSE position, the transmission control module (TCM) sends a serial data message to the body control module (BCM). The message indicates that the gear selector is in the REVERSE position. The BCM applies battery voltage to the backup lamps control circuit illuminating the backup lamps. Once the driver moves the gear selector out of the REVERSE position, a message is sent by the TCM via serial data requesting the BCM to remove battery voltage from the backup lamps control circuit. The engine must be ON for the backup lamps to operate.

Exterior Courtesy Lamps

Hands - Free Liftgate Sensor Lamp (with TC2)

The keyless entry control module supplies battery voltage to the hands - free liftgate sensor lamp located on the lower center section of the rear bumper. The hands - free liftgate sensor lamp illuminates the area where the sensor for the foot activated liftgate actuator is located for hands free liftgate operation. When the keyless entry transmitter is operated to either the lock or unlock functions, the hands - free liftgate sensor lamp is commanded ON by the keyless entry control module. The hands - free liftgate sensor lamp will display the image of the car brand logo on the ground directly under the center of the rear bumper.

Battery Run Down Protection/Inadvertent Power

To provide battery run down protection, the exterior lamps will be deactivated automatically under certain conditions. The BCM monitors the state of the headlamp switch. If the park or headlamp switch is ON when the ignition switch is placed in either the CRANK or RUN position and then placed in the OFF position, the BCM initiates a 10 min timer. At the end of the 10 min, the BCM will turn off the control power output to the park and headlamp relay coils, deactivating the exterior lamps. This feature will be cancelled if any power mode other than OFF becomes active. The BCM will disable battery run down protection if any of the following conditions exist. The park or headlamp switch is placed in the ON to OFF position, and back to the ON position during battery run down protection. The BCM determined that the park or headlamp switch was not active when the ignition was turned OFF.

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