Exterior Lighting Systems Description and Operation
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Exterior Lighting Systems Description and Operation
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The exterior lighting system consist of the following lamps:
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Automatic Headlamp Leveling
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Adaptive Forward Lighting
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Daytime Running Lamps (DRL)
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Park, Tail, License and Marker Lamps
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Low Beam Headlamps (Standard) RPO TT4
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The headlamps consist of a single filament bulb or a high intensity discharge (HID) arc tube and ballast on each side of the vehicle which provide high and low beams.
The headlamps may be turned ON in 3 different ways:
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When the headlamp switch is placed in the ON position, for normal operation
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When the headlamp switch is placed in the AUTOMATIC LIGHT position, for automatic lamp control
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When the headlamp switch is placed in the AUTOMATIC LIGHT position, with the windshield wipers ON in daylight conditions, after a 6 s delay
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The body control module (BCM) controls the headlamps based on the inputs explained above. When a low beam request is received, the BCM supplies an B+ through the headlamp low beam relay for the left headlamp and through daytime running lamp relay - right for the right headlamp. This then applies B+ to the low beam headlamps, illuminating the low beam headlamps. When a high beam request is received, the BCM grounds the headlamp high beam relay control circuit. This energizes the coil in the headlamp high beam relay, causing the relay switch to close. This then applies B+ to both high beam headlamps through the left high beam and right high beam fuses, illuminating the high beam headlamps.
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High Intensity Discharge (HID) Low Beam Headlamps (up level) RPO TT2/TT6
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Warning
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The high intensity discharge system produces high voltage and current. To reduce the risk of severe shocks and burns:
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Never open the high intensity discharge system ballast or the arc tube assembly starter.
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Never probe between the high intensity discharge system ballast output connector and the arc tube assembly.
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The BCM controls the headlamps based on the inputs explained above. When a low beam request is received, the BCM grounds the headlamp low beam relay control circuit. This energizes the coil in the headlamp low beam relay, causing the relay switch to close. This then applies B+ to both low beam HID headlamps through the left low beam and right low beam fuses, illuminating the low beam headlamps. When a high beam request is received, the BCM grounds the headlamp high beam relay control circuit. This energizes the coil in the high beam relay, causing the relay switch to close. This then applies B+ to both low beam HID headlamps through the left high beam and right high beam fuses, illuminating the high beam headlamps.
Run Up Of The Lamp
Each ballast requires higher amperage in order to ensure normal startup and run up of the lamp. Run up is the term used to describe the extra power level given to the bulb. The input current during the steady state operation is lower that the start up amperage. After the lamp receives the strike from the starter and the arc is established, the ballast uses its operating voltage in order to provide the run up power needed in order to keep the lamp ON. The lamp rapidly increases in intensity from a dim glow to a very high intensity, bright light called a steady state. Within a few seconds after the arch has been established in the lamp, most of the stabilizing condition has been completed. Shortly thereafter the stabilizing condition has been attained to 100 percent. A high watt power level is necessary in order to bring the lamp to a steady state in such a short period of time. The high watt power level allows the lamp to meet the SAE light vs. time specification.
When To Change The HID Bulb
An inoperative bulb, end of life occurs when the bulb gets old and becomes unstable. The bulb may begin shutting itself OFF sporadically and unpredictably at first, perhaps only once during a 24 h period. When the bulb begins shutting itself off occasionally, the ballast will automatically turn the bulb back ON again within 0.5 s. The ballast will restrike the bulb so quickly that the bulb may not appear to have shut off. As the bulb ages, the bulb may begin to shut off more frequently, eventually over 30 times per minute. When the bulb begins to shut off more frequently, the ballast receives an extreme amount of repetitive current input . Repetitive and extreme amount restarts or restrikes, without time for the ballast to cool down, will permanently damage the ballast. As a safeguard, when repetitive restrikes are detected, the ballast will not attempt to restrike the lamp. The ballast then shuts down and the bulb goes out.
The following symptoms are noticeable signs of an inoperative bulb:
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Flickering light, caused in the early stages of an inoperative bulb
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Lights go out, caused when the ballast detects, repetitive bulb restrike
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Color change-The lamp may change to a dim pink glow.
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Input power to the ballast must be terminated in order to reset the ballasts fault circuitry. In order to terminate the input power to the ballast, turn the lights OFF and back ON again. Turning the lights OFF and back ON again resets all of the fault circuitry within the ballast until the next occurrence of an extreme amount of repetitive bulb restrike. When an extreme amount of repetitive bulb restrikes occur, replace the starter/arc tube assembly. The ballast will begin the start up process when the starter/arc tube assembly is replaced. Repeatedly resetting the input power can overheat the internal components and cause permanent damage to the ballast. Allow a few minutes of cool down time in between reset attempts.
Inoperative bulbs are often sporadic at first, and difficult to repeat. Inoperative bulbs can be identified by observing if the condition gets progressively worse over the next 100 h of operation.
Light Color
White light has a different color rating than regular headlamps. The range of white light that is acceptable is broad when compared to halogens. Therefore, some variation in headlight coloring between the right and left headlamp will be normal. One HID at the end of the normal range may appear considerably different in color from one at the other end of the range. Difference in color is normal. Replace the arc tube only if the arc tube is determined to be at the bulb inoperative stage.
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Adaptive Forward Lighting
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The adaptive forward lighting consist of the following components:
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Headlamp Control Module
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Headlamp actuator - left
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Headlamp actuator - right
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Dynamic Curve Light
Bend lighting is a function depending on the following signal input values:
The appropriate swivel angle is calculated based on vehicle speed and the steering angle value.
Town Light
Town Light is activated when the vehicle's speed is below 50 km/h (31 mph). Light distribution is reduced to a smaller area in front of the car with a wider light image due to low speed.
Motorway Light (not US/CA)
If vehicle speed is above 90/100 km/h (62 MPH) for a certain time (or once above 120/130 km/h (75/80 MPH) and the corresponding road category is identified, the headlamps will be switched to a motorway light distribution. During motorway light the light output of the HID bulb is increased to 38 W by electrical power management. This improves the visibility range at the far end of the road.
Country Light (not US/CA)
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 50 km/h (31 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 (not US/CA)
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. The function is switched on/off with the same stalk/switch combination. The "high beam flash" has to be activated with the ignition on (System Power Mode = RUN). The "high beam flash" remains activated until the warning indicator within the instrument panel cluster starts flashing (4 s) and an acoustic indication is sent. Then activation takes approx. 3 seconds. An activation flag must be set in the function for adaptive forward lighting ECM and stored in non-volatile memory. Each time the ignition is switched on and the tourist mode is active, the warning indicator is flashing about 4 s. The tourist mode is deactivated with the same procedure described above. The function is switched OFF, if an acoustic signal is sent (Warning indicator remains inactive).
Adverse Weather Light (not US/CA)
Adverse weather light will be switched on while the vehicle speed is below 100 km/h (62 MPH) and the windscreen wipers are activated. The HID bulbs will be powered with different values:
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Left: 38 W, Town Light distribution is adjusted 15 degrees to the left.
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Right: 38 W, Country Light distribution.
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The main advantage is that reflections on the wet floor are reduced to a minimum. This is noticeable as well for oncoming traffic as for the driver. The area in front of the car becomes weaker but with a wider light image.
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 in installed in the car. The rain/light sensor module 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 the rain/light sensor module by switching ON/OFF low beams.
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Flash to Pass (Standard) RPO TT4
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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.
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Flash to Pass (up level) RPO TT2/TT6
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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 sends a message to the headlamp control module to lift the shutter from the Xenon lamp. This causes the Xenon lamp to illuminate the headlamp at full brightness momentarily or until the flash to pass switch is released.
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Automatic Headlamp Leveling
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The Automatic Headlamp Leveling Systems consist of the following components:
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Headlamp leveling actuator - left
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Headlamp leveling actuator - right
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Headlamp Control Module
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Headlamp leveling sensor - front
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Headlamp leveling sensor - rear
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The automatic headlamp leveling system automatically maintains the vertical alignment of the headlamps when the vehicle load and driving conditions change. The headlamp control module receives inputs from the front and rear headlamp leveling sensors to determine vehicle pitch. The headlamp leveling sensors send an output to the headlamp control module as the vehicle suspension compresses and rebounds. The headlamp control module calculates the difference in vehicle pitch and sends a command to the (HID) ballast. The ballast then drive the headlamp leveling actuators to the position commanded by the headlamp control module. The headlamp leveling system also monitors the performance of the HID bulb and ballast. When the headlamp switch is placed in the ON position the headlamps will go down, and then back up to the center position.
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Daytime Running Lamps (DRL) without HID RPO TT4
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The DRL bulbs are combined with the park lamps. One filament is for the DRL and one for the park lamps. The DRL will operate when the following conditions are met:
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The engine is running.
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Headlamp switch in AUTOMATIC LIGHT position.
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The high and low beam headlamps are OFF.
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By turning the headlamp switch in the OFF position the automatic light function and the DRL will be deactivated.
The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2-4.9 V depending on outside lighting conditions. The HVAC control module provides a low reference ground and 5 V reference signals to the ambient light sensor. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either DRL or low beam when the headlamp switch is in the AUTOMATIC LIGHT position. In daylight conditions, the BCM will command the DRL ON by applying ground to the left and right DRL relays via separate left and right DRL relay control circuits. When the BCM applies ground to the relay control circuits, the left and right DRL relay coils energize causing both relay switch contacts to close. With the left and right DRL relay switch contacts closed, battery voltage flows to the left and right DRL lamps. Any function or condition that turns on the headlamps will cancel DRL operation.
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Daytime Running Lamps (DRL) with HID RPO TT2/TT6
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The DRL are LEDs which are continuously illuminated when:
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Ignition is switched ON.
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High and low beam headlamps are ON or OFF.
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Headlamp switch is in PARKING LIGHT, AUTOMATIC LIGHT or LOW BEAM position.
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By turning the headlamp switch in the OFF position the automatic light function and the DRL will be deactivated.
The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2-4.9 V depending on outside lighting conditions. The HVAC control module provides a low reference ground and 5 V reference to the ambient light sensor. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for only DRL or DRL and low beam when the headlamp switch is in the AUTOMATIC LIGHT position. In daylight conditions the BCM will command the DRL ON.
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 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.
When the rear fog lamp switch is placed in the ON position, battery voltage is applied from the BCM to the rear fog lamps. When the rear fog lamp switch is placed in the ON position, battery voltage is applied from the BCM to the rear fog lamps.
When the rear fog lamp switch is placed in the ON position, battery voltage is applied from the BCM to the rear fog lamps.
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Park, Tail, License and Marker Lamps
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The park lamps, tail lamps and license plate lights are turned ON when the headlamp switch is placed in the PARKING LIGHT or LOW BEAM position or anytime the headlights are requested. When the BCM receives a request from the headlamp switch to turn ON the park lamps the BCM a sends out a PWM signal, which illuminates the park lamps, tail lamps and number plate lights.
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.
The repeater lamps are located in the front fender. The repeater lamps are used as additional turn signal lamps, and operate as described in the Turn Signal/Hazard Flasher Lamps description.
The hazard flashers may be activated in any power mode. The hazard warning switch is permanently grounded . When the hazard switch is placed in the ON position, ground is applied through the hazard switch signal circuit to the BCM. The BCM supplies battery voltage to all 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 cluster requesting both turn signal indicators to be cycled ON and OFF.
The brake pedal position (BPP) sensor is used to sense the action of the driver application of the brake pedal. The BPP sensor provides an analog voltage signal that will increase as the brake pedal is applied. The BCM provides a low reference signal and a 5 V reference voltage to the BPP sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery voltage to the stop lamp control circuit and center high mounted stop lamp control circuit . When the control circuit is energized the stop lamps are illuminated.
When the transmission is placed in the reverse position, the engine control module (ECM) sends a serial data message to the BCM. The message indicates that the gear selector is in the reverse position. The BCM applies battery voltage to the backup lamps. The backup lamps are permanently grounded. Once the driver moves the gear selector out of the reverse position, a message is sent by the ECM via serial data requesting the BCM to remove battery voltage from the backup lamp control circuit.
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Battery Run Down Protection/Inadvertent Power
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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 minute timer. At the end of the 10 minutes, 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.
