Lighting and Signalling Systems: Overview

System Description

The horn system consists of the following components

F51UA 15A fuse
Underhood fuse block (contains a non-serviceable PCB Horn relay)
Horn switch
Horn
Body Control Module (BCM)

System Operation

The vehicle horn is activated whenever the horn switch is depressed.
The BCM commands the horns ON under any of the following conditions: When the content theft deterrent system detects a vehicle intrusion-For further information refer to «CONTENT THEFT DETERRENT (CTD) DESCRIPTION AND OPERATION»(ref-652251-S36466070422014082300000) . When the keyless entry system is used to lock the vehicle, a horn chirp may sound to notify the driver that the vehicle has been locked. The notification feature may be enabled or disabled through personalization. For further information refer to «KEYLESS ENTRY SYSTEM DESCRIPTION AND OPERATION (WITHOUT ATH)»(ref-652252-S26237396622014082300000) or «KEYLESS ENTRY SYSTEM DESCRIPTION AND OPERATION (WITH ATH)»(ref-652252-S17677103322014082300000) .

Circuit Operation

The BCM controls the horn operation. When the horn switch is pressed, it closes a switch pulling the horn signal circuit low. When the BCM detects the drop in voltage in the horn switch signal circuit, it energizes the PCB Horn relay which provides B+ voltage to the horn control circuit, sounding the horn.

When the vehicle is in the Off Power Mode the BCM will attempt to detect a stuck or continuously activated horn switch. When enabled, activation of the horn will be limited to 10 seconds to protect the horn from excessive use.

Circuit/System Description

The BCM provides a ground for the Horn PCB relay within the underhood fuse block. The underhood fuse block will then provide B+ voltage to the horn control circuit, sounding the horn.

Description and Operation

HORNS SYSTEM DESCRIPTION AND OPERATION

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 to the body control module (BCM). The BCM will apply battery voltage to the right, left and center stop lamp control circuits and to the trailer brake control module if equipped.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) supplies a voltage reference through the instrument panel cluster dimming voltage reference circuit to the instrument panel cluster lamps dimmer switch, which is part of the headlamp switch. When the dimmer switch is placed in a desired brightness position, reference voltage is applied through the dimmer switch rheostat and the cluster lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage to the LED dimming supply circuit to all related interior lamps, illuminating them to the desired level of brightness.

INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The battery saver mode reduces the parasitic load of some modules during overseas shipment or during vehicle storage conditions. This improves the drain time on the battery of up to 70 days without the battery going dead. When the vehicle is in transport/storage, some features may have reduce functionality as a result being in the battery saver mode, such as disabling the Remote Function Actuator or content theft features.

The battery saver mode incorporates a latching relay that when enabled disconnects some modules from their ignition off power or memory power sources. Battery saver mode is initiated by starting the vehicle and then turning the ignition key into the crank position for greater than 15 seconds. The mode is disengaged by repeating the previous process causing the relay to latch in the other direction. This feature can be used as many times as necessary if the vehicle is to be stored for an extended period of time.

POWER MODE DESCRIPTION AND OPERATION

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.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) energizes the rear fog lamp by applying voltage to the rear fog lamp control circuit. When the rear fog lamp control circuit is energized the rear fog lamp is illuminated.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

When the engine is running and the transmission is placed in reverse gear, the transmission control module 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. Once the driver moves the gear selector out of the reverse position, a message is sent by the transmission control module via serial data requesting the BCM to remove battery voltage from the backup lamp signal circuit. The BCM will not apply battery voltage to the backup lamps if the engine is not running.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

When the body control module (BCM) receives a liftgate open signal, the BCM supplies B+ to the cargo lamp control circuit. This will illuminate the cargo lamp.

INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

When the headlight switch is placed in low beam position, the body control module (BCM) applies a voltage to the low beam headlamps through their respective voltage supply circuits.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) monitors the 12 V signal circuits for the headlamps off signal, headlamps on signal and the park lamp on signal circuits. When the headlight control switch is selected to the desired headlamp function, the signal circuit is pulled to ground and the BCM will detect the voltage drop in that signal circuit and will command the appropriate lights to turn on or turn off.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) supplies a reference voltage to the backlight dimmer switch, which is part of the headlamp switch. When the backlight dimmer switch is placed in a desired brightness position, reference voltage is applied to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage to the LED dimming supply circuit to all related interior lamps, illuminating them to the desired level of brightness.

INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The headlamp control module calculates the headlamp angle and sends commands to the left and right adaptive forward lighting system headlamp actuators. The headlamp actuators drive the headlamps to the position commanded by the headlamp control module. The headlamp control module monitors the headlamp actuator motor control circuits for proper circuit continuity and for shorts to ground or voltage. If a malfunction is detected, a DTC will be stored in memory and the driver will be notified with a message displayed over the driver information center located on the instrument cluster.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The headlamp high beam relay is supplied with battery voltage at all times. The turn signal/multifunction switch signal circuit is grounded by pressing the turn signal/multifunction switch. The body control module (BCM) energizes the headlamp high beam relay by applying ground to the headlamp high beam relay control circuit. When the headlamp high beam relay is energized, the relay switch contacts close and battery voltage is applied through the high beam lamp fuses to the high beam lamp supply voltage circuit which illuminates the high beam lamps.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) energizes the park lamps by applying voltage to the park lamp control circuit. When the park lamp control circuit is energized, the park lamps are illuminated.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

When the headlight switch is placed in low beam position, the body control module (BCM) energizes the low beam headlamp relay which supplies battery voltage to the respective headlamp control circuits.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

When the headlight switch is in the Auto position and the ambient light sensor detects sunlight, the body control module (BCM) will command the daytime running lamps to illuminate by providing 12 volts to the daytime running lamp control circuit.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) supplies a reference voltage to the backlight dimmer switch, which is part of the headlamp switch. When the backlight dimmer switch is placed in a desired brightness position, reference voltage is applied via the backlight dimmer switch rheostat to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage to the LED dimming supply circuit to all related interior lamps, illuminating them to the desired level of brightness.

INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The headlamp switch is supplied with ground at all times. When the headlamp switch is placed in either the park or low beam position, ground is applied to the tail lamp signal circuit to the body control module (BCM). The BCM responds by applying battery voltage to the left/right park lamps, left/right side marker lamps and left/right tail lamps. This energizes the appropriate lamp.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

Battery voltage for the courtesy lamps is supplied at all times to the body control module (BCM). When the BCM receives a signal to command the courtesy lamps ON, it then applies voltage through the courtesy lamps control circuits to the courtesy lamps.

INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The body control module (BCM) supplies a reference voltage to the backlight dimmer switch, which is part of the headlamp switch. When the dimmer switch is placed in a desired brightness position, the dimmed voltage setting is applied through the dimmer switch and the dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the backlight lamp control circuit and the LED dimming control circuit illuminating the components to the requested level.

INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 1.4-4.5 V depending on outside lighting conditions. The body control module (BCM) monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights or automatic lamp control when the headlamp switch is in the AUTO position. In daylight conditions the BCM will command the daytime running lights ON. During low light conditions the BCM will command the low beam headlamps ON.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) uses the ambient light sensor to determine which brightness of the accent lighting is needed. The BCM applies a pulse width modulated (PWM) voltage through the accent light LED control circuit. Depending on the specified lighting requirements, the BCM has three different accent lighting settings

Daylight conditions (70%)
Night conditions (40%)
Welcome light (100%)

INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) supplies a voltage reference through the backlight dimmer switch, which is part of the headlamp switch. When the dimmer switch is placed in a desired brightness position, reference voltage is applied through the backlight dimmer switch to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the backlight lamp control circuit. This will illuminate the ignition mode switch halo lamp.

INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The front and rear suspension position sensors provide the headlamp control module with front and rear suspension position information. Each sensor receives a 5V reference, signal, and low reference circuits from the headlamp control module. The sensors are connected to the control arms at the front and rear suspension. As the vehicle travels, the suspension compresses and rebounds moving the suspension position sensor arms. This causes the signal output of the sensors to change. The headlamp control module compares the information from the front and rear suspension position sensors and adjusts the headlamp leveling as needed.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) supplies a reference voltage to the backlight dimmer switch, which is part of the headlamp switch. When the backlight dimmer switch is placed in a desired brightness position, reference voltage is applied through the backlight dimmer switch resistor ladder to the BCM. The BCM interprets this voltage signal and will command the interior lights to the desired brightness, command the front fog lamps or the rear fog lamps depending upon the switch setting selected.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

When the hazard switch is placed in the ON position, ground is momentarily applied through the hazard switch signal circuit to the body control module (BCM). The BCM will detect this voltage drop and will supply 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 (IPC) requesting both turn signal indicators to be cycled ON and OFF.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The BCM monitors the voltage level within the high beam signal circuit and the flash to pass signal circuit. When the turn signal/multifunction switch is moved to the high beam position or to the flash to pass position, the voltage within the appropriate signal circuit drops to less than 1 V. The BCM will detect the voltage drop and will command the headlamp high beams to turn ON or OFF.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The headlamp switch is supplied with ground at all times. When the headlamp switch is placed in either the park or low beam position, the BCM responds by applying battery voltage to the license plate lamp control circuit. This energizes the left and right license lamp.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

EXTERIOR LIGHTS SCHEMATICS

The trailer brake control module will receive a serial data message from the body control module (BCM) indicating that the vehicle park lamps have been activated. The trailer brake control module will then apply system voltage to the trailer tail lamps through their respective voltage supply circuits.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The trailer brake control module will receive a serial data message from the BCM indicating that the vehicle left turn signal lamp or the right turn signal lamp has been activated. The trailer brake control module will then apply a pulsating voltage to the appropriate trailer turn signal lamps through their respective voltage supply circuits.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The trailer brake control module will receive a serial data message from the BCM indicating that the vehicle brake lamps have been activated. The trailer brake control module will then apply system voltage to the trailer stop lamps through their respective voltage supply circuits.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The trailer park lamp relay is supplied with battery voltage at all times. The trailer park lamp signal circuit is grounded by turning the headlamp switch. The body control module (BCM) energizes the trailer park lamp relay by applying ground to the trailer park lamp relay control circuit. When the trailer park lamp relay is energized, the relay switch contacts close and battery voltage is applied through the trailer park lamp relay fuse to the trailer park lamp supply voltage circuit which illuminates the trailer park lamps if a trailer is connected.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The trailer brake control module will receive a serial data message from the BCM indicating that the vehicle backup lamps have been activated. The trailer brake control module will then apply system voltage to the trailer backup lamps through their respective voltage supply circuits.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The trailer brake control module will receive a serial data message from the BCM indicating that the vehicle rear fog lamps have been activated. The trailer brake control module will then apply system voltage to the trailer fog lamps through their respective voltage supply circuits.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

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.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

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 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 lamp control circuit and center high mounted stop lamp control circuit. When the control circuit is energized the stop lamps are illuminated.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The stop lamp switch signal circuit is a B+ input from the body control module (BCM) to the engine control module (ECM). The ECM monitors the stop lamp switch circuit to detect when the brake pedal has been applied. The BCM monitors the brake pedal position sensor to determine when the brake pedal is applied. When the brake pedal is applied, the BCM supplies 12V on the stop lamp switch signal circuit and also sends a serial data message to the ECM indicating that the brake pedal has been applied.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) monitors the horn switch signal circuit, when the horn pad is pressed, the BCM detects the drop in the horn switch signal circuit and provides a ground for the Horn PCB relay within the underhood fuse block. The underhood fuse block will then provide B+ voltage to the horn control circuit, sounding the horns

HORNS SYSTEM DESCRIPTION AND OPERATION

Battery positive voltage is applied to the headlamp control module at all times. The headlamp control module has a normal operational voltage range of about 12.5-16 V and is only fully functional with the ignition switch is in the RUN position and the headlamp switch in the AUTOMATIC LIGHT position. The communications enable signal from the body control module (BCM) wakes the headlamp control module microprocessor. The headlamp control module receives serial data messages from the engine control module, transmission control module, electronic brake control module, and BCM with information regarding power mode, speed, steering angle, transmission gear selection, and headlamp switch status. The headlamp control module calculates the headlamp angle and sends commands to the left and right adaptive forward lighting system headlamp actuators. The headlamp actuators drive the headlamps to the position commanded by the headlamp control module. The headlamp control module monitors the headlamp actuator motor control circuits for proper circuit continuity and for shorts to ground or voltage. If a malfunction is detected, a DTC will be stored in memory and the driver will be notified with a message displayed over the driver information center located on the instrument cluster.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

Battery voltage for the courtesy lamps is supplied at all times to the body control module (BCM). When the BCM receives a signal to command the courtesy lamps ON, it then applies voltage through the dome/courtesy lamps control circuit to the courtesy lamps.

INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) supplies a reference voltage to the backlight dimmer switch, which is part of the headlamp switch. When the backlight dimmer switch is placed in a desired brightness position, reference voltage is applied through the backlight dimmer switch resistor ladder to the BCM. The BCM interprets this voltage signal and will command the interior lights to the desired brightness, command the front fog lamps or the rear fog lamps depending upon the switch setting selected.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The vehicle headlamps are controlled by the body control module (BCM) based on inputs from the headlamp switch and the turn signal/multifunction switch. The headlamp switch has four positions: OFF, AUTOMATIC LIGHT, PARKING LIGHT, and LOW BEAM. The default headlamp switch position is AUTOMATIC LIGHT, in which the BCM uses the ambient light sensor to determine when headlamps are needed. The OFF portion of the headlamp switch is a momentary switch which overrides the automatic headlamp and will turn OFF the vehicle headlamps. When in the OFF position, the headlamp switch grounds the headlamp switch headlamps OFF signal circuit, prompting the BCM to turn OFF the headlamps. The Park position of the headlamp switch will only illuminate the vehicle parking lamps. The LOW BEAM position of the headlamp switch will illuminate both the parking lamps, as well has the headlamps. With the headlamp switch in the LOW BEAM position, the headlamp switch headlamps on signal circuit is grounded, prompting the BCM to turn on the headlamps, regardless of other factors such as ambient light.

The headlamp high beams are controlled through the flash to pass switch and the headlamp dimmer switch, both located in the turn signal/multifunction switch. The flash to pass switch is a momentary type switch, designed to illuminate the high beams as long as the switch is held. With the switch closed, the flash to pass switch signal circuit is grounded, prompting the BCM to turn on the high beam lamps. The headlamp dimmer switch allows the operator to select between full time high or low beam operation. Unlike the flash to pass switch, it is not a momentary switch. When the headlamp dimmer switch is in the high beam position, the headlamp dimmer switch high beam signal circuit is grounded. This prompts the BCM to turn on the high beam lamps.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

Each headlamp assembly contains a headlamp leveling motor that is controlled by the headlight switch. The headlight switch is a resistance ladder switch and wired to the headlamp leveling motors. With the ignition in ON position the headlight switch ON, the headlamp leveling motors are supplied with a specific voltage depending upon the position of the headlamp leveling switch. With the switch in the 0 position, no voltage is supplied to the headlamp leveling motors and the headlamp aiming will be at the factory specifications. Each switch selection will provide the headlamp leveling motors with incrementally increased voltage levels changing the headlamp aiming.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

Battery positive voltage is applied to the headlamp control module at all times. The headlamp control module has a normal operational voltage range of about 12.5-16 V and is only fully functional with the ignition switch is in the RUN position and the headlamp switch in the AUTOMATIC LIGHT position. The communications enable signal from the body control module (BCM) wakes the headlamp control module microprocessor. The headlamp control module receives serial data messages from the engine control module (ECM), transmission control module (TCM), electronic brake control module (EBCM), and BCM with information regarding power mode, speed, steering angle, transmission gear selection, and headlamp switch status. The headlamp control module calculates the headlamp angle and sends commands to the left and right adaptive forward lighting system headlamp actuators. The headlamp actuators drive the headlamps to the position commanded by the headlamp control module. The headlamp control module monitors the headlamp actuator motor control circuits for proper circuit continuity and for shorts to ground or voltage. If a malfunction is detected, a DTC will be stored in memory and the driver will be notified with a message displayed over the driver information center located on the instrument cluster.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The body control module (BCM) uses the ambient light sensor to determine which brightness of the accent lamps is needed. The BCM provides B+ voltage to the individual accent lamps via the accent lamps control circuit.

INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The park lamps, tail lamps and license plate lights are turned ON when the headlamp switch is placed in the PARK or LOW BEAM position or anytime the headlights are requested. When the body control module (BCM) receives a request from the headlamp switch to turn ON the park lamps the BCM a sends out a voltage on the control circuit, which illuminates the park lamps, tail lamps and license plate lights.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

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 lamp control circuit and center high mounted stop lamp control circuit. When the control circuit is energized the stop lamps are illuminated.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

The trailer brake control module will receive a serial data message from the BCM indicating when each of the vehicle exterior lights have been activated. The trailer brake control module will then apply voltage to the appropriate trailer lamps through their respective voltage supply circuits.

EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

Lighting and Signalling Systems: Overview Saab 9-4X I

System Description

System Operation

Circuit Operation

Circuit/System Description

Description and Operation

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