Lighting System: Overview GMC Acadia I

Circuit/System Description

The body control module (BCM) supplies a voltage reference through the instrument panel (I/P) dimming voltage reference circuit to the interior lamp 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 I/P lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the I/P lamps supply voltage circuit and the LED dimming supply circuit to all related interior lamps, illuminating them to the desired level of brightness.

On vehicles equipped with adaptive forward lighting, the headlamps can turn left and right to improve visibility during turns.

Voltage is applied at all times to the fog lamp relay. When the fog lamp switch is placed in the ON position, a ground signal is applied to the body control module (BCM) through the fog lamp switch signal circuit. The BCM then applies a ground to the fog lamp relay control circuit. This engages the fog lamp relay and applies voltage through the FOG LAMP fuse to the front fog lamps.

When the PRNDL is placed in the REVERSE position, a signal is sent to the body control module (BCM). The BCM then applies voltage through the backup lamps control circuit to the back up lamps. The engine may need to be running for the backup lamps to function.

The low beam headlamps are controlled by the body control module (BCM). The BCM grounds the headlamp low beam relay control circuit in order to energize the HID/LO BEAM relay coil. The HID/LO BEAM relay then sends voltage to the low beam headlamps.

When the headlamp switch is in the OFF position, the body control module (BCM) receives a ground signal through the headlamp switch OFF circuit and an open signal on the park lamp ON circuit and headlamps ON circuit. When the headlamp switch is in the PARK or HEAD position, the BCM receives an open signal through the headlamp switch OFF circuit and a ground signal through the park lamp ON circuit or headlamp ON circuit.

On vehicles equipped with adaptive forward lighting, the headlamps can turn left and right to improve visibility during turns.

On vehicles equipped with adaptive forward lighting, the headlamps can turn left and right to improve visibility during turns.

When the body control module (BCM) receives a ground signal from the multifunction high beam or flash to pass (FTP) switch commanding to illuminate the high beam headlamps, the BCM will energize the high beam relay by grounding the high beam relay control circuit.

Battery positive voltage is supplied to the PRK LAMP relay at all times. The body control module (BCM) grounds the park lamp relay control circuit in order to activate the relay. With the park lamp relay activated, voltage is supplied to the park lamp control circuit illuminating the park lamps, license lamps, and marker 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 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. 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 (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying ground to the DRL relay via the DRL relay control circuit. When the BCM applies ground to the DRL relay control circuit, the DRL relay coil energizes causing the relay switch contacts to close. With the DRL relay switch contacts closed, battery voltage flows through the DRL fuse to the left and right DRL lamps. Any function or condition that turns on the headlamps will cancel DRL operation.

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 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. 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 (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying ground to the DRL 2 relay via the DRL 2 relay control circuit. When the BCM applies ground to the DRL 2 relay control circuit, the DRL 2 relay coil energizes causing the relay switch contacts to close. With the DRL 2 relay switch contacts closed, battery voltage flows through the DRL 2 fuse to the left and right DRL lamps. Any function or condition that turns on the headlamps will cancel DRL operation.

The body control module (BCM) supplies a voltage reference through the instrument panel (I/P) dimming voltage reference circuit to the interior lamp 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 I/P lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a variable voltage through the LED backlight lamp control circuit illuminating the components listed below, if equipped

1. Clock
2. Console flood lamp
3. Diver information center (DIC) switch
4. Driver window switch
5. Headlamp switch
6. Head up display (HUD) Switch
7. Heated seat switches
8. HVAC control head
9. I/P switch assembly
10. Radio
11. Rear seat audio (RSA) control
12. Rear video/HVAC control
13. Steering wheel control switch

Battery voltage for the courtesy lamps is supplied at all times, from the BCM and INAD/PWR/LED Fuse located in the I/P fuse block, 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 listed below.

1. Left and right footwell lamps
2. Left and right liftgate lamps
3. Courtesy/reading lamps
4. Cargo lamp

The body control module (BCM) supplies a voltage reference through the instrument panel (I/P) dimming voltage reference circuit to the interior lamp 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 I/P lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal then applies a pulse width modulated (PWM) voltage through the LED dimming supply circuit illuminating the heated seat switches to the requested level.

The ambient light sensor is used to monitor outside lighting conditions. The body control module (BCM) provides a 5-volt reference signal to the ambient light sensor. The sensor is a variable resistor, it's resistance changes as outside lighting conditions changes. With the headlamp switch in the AUTO position, the BCM monitors the sensor signal circuit to determine if the outside lighting conditions are correct for either daytime running lamps (DRL) or headlamp low beam operation. In daylight conditions, the BCM will command the DRLs ON. In low light conditions, the BCM will command the low beam headlamps ON.

The body control module (BCM) supplies a voltage reference through the instrument panel (I/P) dimming voltage reference circuit to the interior lamp dimmer switch, which is part of the headlamp switch. When the dimmer switch is placed in a desired position, reference voltage is applied through the dimmer switch rheostat and the I/P lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the instrument panel lamp control circuits illuminating the components listed below, if equipped.

1. Hazard Switch
2. I/P Cluster
3. Power Window Switches
4. Sunroof Switch
5. Garage Door Opener Transmitter

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 right and left stop lamp control circuits and center high mounted stop lamp (CHMSL) control circuit. The stop lamps on this vehicle will not illuminate unless the ignition is in the accessory, run, or crank positions. When the ignition is in the OFF position the stop lamps will not illuminate when the brake pedal is applied.

The instrument panel (I/P) dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The body control module (BCM) supplies a 12-volt reference through the instrument panel (I/P) dimming voltage reference circuit to the interior lamp 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 I/P lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the I/P lamps control circuit and the LED dimming control circuit to all related interior lamps, illuminating them to the desired level of brightness.

The body control module (BCM) provides a 5-volt reference voltage and a low reference signal to the brake pedal position sensor (BPPS). When the brake pedal is applied, the BPPS sends a variable voltage signal, that will increase as the brake pedal is applied, through the brake apply sensor signal circuit to the BCM. In response to this signal, the BCM applies B+ to the stop lamps, center high mounted stop lamp (CHMSL), transmission control module (TCM), and engine control module (ECM). The stop lamps will not operate unless the ignition is in the ON position.

The body control module (BCM) provides a 5-volt reference voltage and a low reference signal to the brake pedal position sensor (BPPS). When the brake pedal is applied, the BPPS sends a variable voltage signal, that will increase as the brake pedal is applied, through the stop lamp switch signal circuit to the BCM. The BCM then applies a signal through the stop lamp switch signal circuit to the engine control module (ECM) and transmission control module (TCM).

The stop lamp switch signal circuit is a direct hardwire input to the transmission control module (TCM) from the body control module (BCM). The TCM module monitors the stop lamp signal circuit in order to detect when the brake pedal has been applied. When the brake pedal is pressed, the BCM sends a High Speed GM Lan message to the engine control module (ECM) indicating that the brake pedal has been applied. The BCM also sends a high voltage signal on the stop lamp signal circuit to the TCM module. The TCM module sends a universal asynchronous receiver transmitter low speed GM Lan message to the ECM indicating that a brake pedal application has occurred. The ECM will compare the GM LAN Low speed and GM LAN High Speed data message in order to confirm that both serial data messages match.

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.

When the PRNDL is placed in the REVERSE position, a serial data signal is sent from the transmission control module (TCM) to the body control module (BCM). The BCM then applies voltage through the backup lamps control circuit to the tail lamp assemblies illuminating the backup lamps. The engine may need to be running for the backup lamps to function.

The courtesy lamps are controlled by the body control module (BCM). Inputs from the dome lamp switch and the door ajar switches are monitored by the BCM. When a door ajar switch is closed, or the dome lamp switch is turned to the ON position, the BCM supplies the B+ for the courtesy lamps.

The body control module (BCM) controls the fog lamps based on inputs from the fog lamp switch. When the fog lamp switch is pressed, a ground path is provided on the front fog lamp switch signal circuit to the BCM, indicating the front fog lamps ON command. In response to this signal, the BCM grounds the fog lamp relay control circuit energizing the FOG LAMP Relay. With the fog lamp relay energized, battery voltage is applied through the FOG LAMPS Fuse and the fog lamp control circuits illuminating the front fog lamps.

When a fog lamp request is seen by the BCM, a serial data message is sent to the instrument panel cluster (IPC) requesting the fog lamp indicator be illuminated.

The body control module (BCM) controls the hazard lamps based on inputs from the hazard switch. With the hazard switch closed, a ground path is provided on the hazards switch signal circuit, indicating a hazard lamp request. When this request is seen, the BCM will pulse the turn signal lamp control circuits, illuminating the turn signal lamps.

With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the headlamp switch. In response to this input, the body control module (BCM) provides ground to either the headlamp low beam relay control circuit or the headlamp high beam relay control circuit. The position of the turn signal/multifunction switch determines which relay coil is supplied with ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery voltage to the relay coil and switch circuits. The low beam headlamps operate when the BCM grounds the relay coil control circuit to the relay coil of the low beam relay. This energizes the low beam relay causing the switch contacts to close. With the switch contacts closed, battery voltage is applied to the LT LO and RT LO beam fuses through to the left and right low beam headlamps.

With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the headlamp switch. In response to this input, the body control module (BCM) provides ground to either the headlamp low beam relay control circuit or the headlamp high beam relay control circuit. The position of the turn signal/multifunction switch determines which relay coil is supplied with ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery voltage to the relay coil and switch circuits. The low beam headlamps operate when the BCM grounds the relay coil control circuit to the relay coil of the low beam relay. This energizes the low beam relay causing the switch contacts to close. With the switch contacts closed, battery voltage is applied to the LT LO and RT LO beam fuses through to the left and right low beam headlamps. When the headlamp high beam relay coil is energized, current flows through the LT HI and the RT HI beam fuses to the high beam headlamps. With the turn signal/multifunction switch in the high beam position the BCM sends a serial data message to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator.

The body control module (BCM) supplies a voltage reference through the instrument panel (I/P) dimming 12 V reference circuit to the interior lamp 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 I/P lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the instrument panel lamp control circuit, the backlight lamp control circuit, and the LED dimming control circuit illuminating the LED and I/P panel lamps.

The park, tail, marker, and license lamps are turned ON when the headlamp switch is placed in the PARK or ON position or anytime the headlights are requested. The underhood fuse block supplies B+ to both the park lamp relay switch contacts and the park lamp coil circuit. The body control module (BCM) provides a ground or control circuit to the park lamp circuit. When the park lamps are requested ON, the BCM energizes the park lamp relay. Current flow is from the park lamp relay to the individual park lamp circuit fuses and to their respective park, tail, marker, and license 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 B+ to the stop lamps, center high mounted stop lamp (CHMSL), transmission control module (TCM), and engine control module (ECM). The stop lamps will not operate unless the ignition is in the ON position.

The body control module (BCM) controls the vehicle turn signals based on inputs from the turn signal/multifunction switch. With the turn signal/multifunction switch in the left turn position, a ground path is provided on the left turn signal switch signal circuit, indicating a left turn signal request. With the turn signal/multifunction switch in the right turn position, a ground path is provided on the right turn signal switch signal circuit, indicating a right turn signal request. When the specific request is seen, the BCM will pulse the respective turn signal lamp control circuits, illuminating the turn signal lamps.

When a turn signal request is seen by the BCM, a serial data message is sent to the instrument panel cluster (IPC) requesting the respective turn signal indicator be pulsed.