Exterior Lamps - Operation

OPERATION

Following are paragraphs that briefly describe the operation of each of the major exterior lighting systems. The lamps and the hard wired circuits between components related to the exterior lighting system may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds.

However, conventional diagnostic methods will not prove conclusive in the diagnosis of the exterior lighting system or the electronic controls or communication between modules and other devices that provide some features of the exterior lighting system. The most reliable, efficient, and accurate means to diagnose the exterior lighting system or the electronic controls and communication related to exterior lighting system operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.

AUTOMATIC HEADLAMPS

The optional automatic headlamp system includes the Steering Control Module (SCM), the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN), the Front Control Module (FCM), the left (lighting) multi-function switch, depending upon vehicle equipment either the sun load sensor on the top of the instrument panel or the Rain Sensor Module (RSM) (also known as the Rain Light Sensor Module/RLSM) on the inside of the windshield below the upper windshield opening header.

First, the A (Automatic) position must be selected using the left multi-function switch. Once this prerequisite has been met, the SCM responds by sending the appropriate electronic headlamp switch and headlamp beam select switch status messages to the EMIC over the LIN data bus. Either the sun load sensor provides an ambient light level input to the EMIC, which is relayed to the FCM over the CAN data bus, or the RSM provides electronic ambient light level input to the EMIC, which is relayed to the FCM over the CAN data bus. The EMIC then sends the appropriate electronic headlamp and headlamp beam request messages to the FCM over the CAN data bus. With the engine running, the FCM responds to these messages by automatically controlling a pulse width modulated voltage output to the selected headlamp lighting elements through the right and left low beam feed circuits to illuminate the headlamps. The FCM also sends the appropriate electronic messages back to the EMIC to control the illumination of the high beam indicator.

BACKUP LAMPS

The backup (or reverse) lamps have a path to ground at all times through a takeout and eyelet terminal of the body wire harness that is secured by a ground screw to the body sheet metal. The Powertrain Control Module (PCM) or the Transmission Control Module (TCM) continually monitors a hard wired multiplex input from the Transmission Range Sensor (TRS), then sends the proper electronic transmission gear selector status messages to other electronic modules over the CAN data bus. Whenever the ignition switch is in the ON position and the FCM receives an electronic message indicating the status of the transmission gear selector is REVERSE, it provides a battery voltage output to the backup lamps on the backup lamp feed circuit.

BRAKE LAMPS

The brake (or stop) lamps and the Center High Mounted Stop Lamp (CHMSL) each have a path to ground at all times through a takeout and eyelet terminal of the body wire harness that is secured by a ground screw to the body sheet metal within the passenger compartment. The brake lamps and CHMSL receive battery voltage on the brake lamp switch feed circuit when the brake lamp switch is closed by the brake pedal arm. The CHMSL and brake lamps are connected to a hard wired output from the brake lamp switch. On vehicles so equipped, the brake lamp function of the trailer tow stop/turn relays is controlled by an output from the FCM based upon a hard wired input from the brake lamp switch.

DAYTIME RUNNING LAMPS

Vehicles manufactured for sale in Canada illuminate the high beam bulbs of both headlamp bulbs at a reduced intensity when the engine is running, the parking brake is released, the automatic transmission gear selector is not in the PARK position and the exterior lamps are turned OFF. The FCM must be programmed appropriately for this feature to be enabled. Once enabled, anytime the FCM receives electronic messages over the CAN data bus from the Powertrain Control Module (PCM) indicating the engine is running, from the EMIC indicating the status of the left (lighting) multi-function switch input is in the OFF or A (Automatic) positions and indicating that the parking brake lever is released, the FCM provides a pulse width modulated voltage output to the headlamp high beam bulb filaments through the right and left high beam feed circuits to produce illumination at a reduced intensity.

FRONT FOG LAMPS

Vehicles equipped with optional front fog lamps include a front fog lamp relay installed in the Integrated Power Module (IPM), and a front fog lamp switch integral to the left (lighting) multi-function switch on the steering column. The front fog lamps have a path to ground at all times through their connection to the headlamp and dash wire harness. The headlamp and dash wire harness has takeouts with eyelet terminals that are secured by ground screws to the front end sheet metal within the engine compartment. The SCM monitors a hard wired multiplex input from the left multi-function switch to determine whether the fog lamps are selected, then sends electronic front fog lamp switch status messages to the EMIC over the LIN data bus and the EMIC relays an electronic front fog lamp request message to the FCM over the CAN data bus.

When the FCM receives a front fog lamp request message it then controls front fog lamp operation by energizing or de-energizing the front fog lamp relay control coil. The FCM also sends the appropriate electronic message to the EMIC to illuminate or extinguish the front fog lamp indicator. When the front fog lamp relay is energized, it provides battery voltage from a fused B(+) fuse in the IPM to the fog lamps through the fog lamp relay output circuit. In vehicles manufactured for domestic markets, the FCM will automatically de-energize the front fog lamp relay any time the headlamp high beams are selected.

The FCM also provides a battery saver (load shedding) feature for the front fog lamps, which will turn these lamps OFF if they are left ON for more than about eight minutes with the ignition switch in the LOCK position. The FCM will also turn OFF the front fog lamps if it detects that system voltage is less than 11.75 volts for more than about 30 seconds, and will return the front fog lamps to normal operation when it detects that system voltage is greater than 13.0 volts for greater than 30 seconds.

Each front fog lamp includes an integral adjustment screw to be used for static aiming of the fog lamp beams.

HAZARD WARNING LAMPS

The hazard warning system includes the EMIC, the FCM and the hazard switch in the upper switch pod located in the center stack area of the instrument panel, above the air conditioner and heater controls. The FCM monitors a hard wired input from the hazard switch through an internal pull-up to determine the status of the hazard switch.

When the FCM receives an input from the hazard switch it controls hazard warning system operation and flash rate by controlling a battery voltage outputs through high side drivers on the right and left turn signal feed circuits. The FCM also sends the appropriate electronic messages back to the EMIC over the CAN data bus to control the illumination and flash rate of the right and left turn signal indicators, as well as to control the click rate of an electromechanical relay soldered onto the EMIC electronic circuit board that emulates the sound emitted by a conventional hazard warning flasher. The EMIC then sends messages to the upper instrument panel switch pod over the LIN data bus to control the illumination of the hazard switch push button.

HEADLAMPS

The headlamp system includes the left (lighting) multi-function switch, the SCM, the EMIC and the FCM. Each headlamp bulb has a path to ground at all times through their connection to the headlamp and dash wire harness. The headlamp and dash wire harness has takeouts with eyelet terminals that are secured by ground screws to the front end sheet metal within the engine compartment.

The SCM monitors a hard wired multiplex input to determine the status of the left multi-function switch and whether the headlamp high or low beams are selected. The SCM then sends the appropriate electronic headlamp switch and headlamp beam select switch status messages to the EMIC over the LIN data bus. The EMIC then relays the appropriate electronic headlamp and headlamp beam request messages to the FCM over the CAN data bus. The FCM responds to these messages by providing a pulse width modulated voltage output to the proper halogen headlamp bulbs through the right and left low and high beam feed circuits to illuminate the selected headlamp beams. The FCM also sends the appropriate electronic messages to the EMIC to control the illumination of the high beam indicator.

The FCM provides a battery saver (load shedding) feature for the headlamps, which will turn these lamps OFF if they are left ON for more than about eight minutes with the ignition switch in the LOCK position. The SCM and the EMIC each provide a fail-safe feature for the headlamps, which will cause the FCM to turn the low beam headlamps ON automatically if there is no input available from the left multi-function switch. The FCM also provides a fail-safe feature for the headlamps that will turn the headlamps ON automatically whenever a loss of CAN bus communication is detected with the ignition switch in the ON position.

Each headlamp includes an integral reflector adjustment screw to be used for static aiming of the headlamps.

HEADLAMP DELAY

The headlamp delay feature includes the left (lighting) multi-function switch, the SCM, the EMIC and the FCM. This feature has customer programmable delay intervals. If the left multi-function switch remains in the headlamp ON position until after the ignition switch is turned to the OFF position, then the headlamps will remain illuminated until after the selected delay interval has elapsed. The park lamps will not stay ON during the headlamp delay interval. The default delay interval is zero seconds (disabled), but can be reprogrammed by the customer using the customer programmable features function of the EVIC.

HEADLAMP LEVELING

In certain export markets where required, a manual headlamp leveling system is provided on the vehicle. The manual headlamp leveling system includes unique front lamp units equipped with a headlamp leveling actuator motor, and a thumbwheel-actuated headlamp leveling switch integral to the upper switch pod on the instrument panel center stack. The manual headlamp leveling system allows the headlamp beams to be adjusted to one of four vertical positions to compensate for changes in inclination caused by the loading of the vehicle suspension.

The leveling motors are mechanically connected through an integral pushrod to the adjustable headlamp reflector. Each time the headlamp leveling switch is rotated to one of the four detent positions, the circuitry of the switch provides a voltage signal to the electronic circuitry of both leveling actuator motors. The electronic circuitry of these stepper motors responds to the voltage inputs received from the switch to move the headlamp reflectors to the selected position.

The headlamp leveling motors and switch have a path to ground at all times. The headlamp leveling components operate on battery current received only when the exterior lighting is turned ON.

PARK LAMPS

The park lamps system includes the SCM, the EMIC, the FCM, a park lamp relay installed in the Integrated Power Module (IPM), and the left (lighting) multi-function switch on the steering column. The front park lamp and side marker or position lamp bulbs each have a path to ground at all times through their connection to the headlamp and dash wire harness. The headlamp and dash wire harness has takeouts with eyelet terminals that are secured by ground screws to the front end sheet metal within the engine compartment. The rear park lamp, side marker lamp and license plate lamp bulbs have a path to ground at all times through a takeout and eyelet terminal of the body wire harness that is secured by a ground screw to the body sheet metal within the passenger compartment.

The SCM monitors a hard wired multiplex input from the left multi-function switch, then sends the appropriate electronic headlamp switch status messages to the EMIC over the LIN data bus. Then the EMIC relays the appropriate electronic message to the FCM over the CAN data bus. The FCM responds to these messages by energizing or de-energizing the park lamp relay. When the park lamp relay is energized, it provides battery voltage through a park lamp relay output circuit and fuses in the IPM to the appropriate lamp bulbs. The FCM and SCM also send the appropriate electronic messages to the EMIC to control the illumination and lighting level of the panel lamps.

For domestic market vehicles, the FCM provides a battery saver (load shedding) feature for the park lamps, which will turn these lamps OFF if they are left ON for more than about eight minutes with the ignition switch in the LOCK position. The SCM and the EMIC each provide a fail-safe feature for the park lamps, which will send an electronic message to the FCM to turn these lamps ON automatically if there is no input available from the left multi-function switch. The FCM also provides a fail-safe feature for the headlamps that will turn the headlamps ON automatically whenever a loss of CAN bus communication is detected with the ignition switch in the ON position.

REAR FOG LAMPS

Rear fog lamps are installed on vehicles manufactured for all export markets. The rear fog lamp system includes a rear fog lamp relay installed in the IPM, the left (lighting) multi-function switch, the SCM, the EMIC and the FCM. The rear fog lamps have a path to ground at all times through their connection to the rear fascia wire harness.

The SCM monitors a hard wired multiplex input from the left multi-function switch to determine whether the rear fog lamps are selected, then sends electronic rear fog lamp switch status messages to the EMIC over the LIN data bus. Then the EMIC relays an electronic rear fog lamp request messages to the FCM over the CAN data bus. When the FCM receives a rear fog lamp request message it controls rear fog lamp operation by energizing or de-energizing the rear fog lamp relay control coil.

The FCM also sends the appropriate electronic messages back to the EMIC to illuminate or extinguish the rear fog lamp indicator. When the rear fog lamp relay is energized, it provides battery voltage from a fused B(+) fuse in the IPM to the rear fog lamps through the rear fog lamp relay output circuit.

The FCM will automatically de-energize the rear fog lamp relay any time the front fog lamps are deselected or when the automatic headlamps feature turns the headlamps OFF. However, on vehicles with the automatic headlamps option, the rear fog lamps must always be turned ON manually, even after they've been turned OFF automatically. The FCM also provides a battery saver (load shedding) feature for the rear fog lamps, which will turn these lamps OFF if they are left ON for more than about eight minutes with the ignition switch in the LOCK position.

On vehicles with a factory-installed trailer towing package including the Trailer Module (TM), the FCM will suppress operation of the rear fog lamps on the vehicle whenever a trailer is connected, while the TM operates the rear fog lamps on the trailer.

SMARTBEAM(R) SYSTEM

The optional SmartBeam(R) (auto high beam) system includes the SmartBeam(R) module with digital imager camera and electronic circuitry integral to the electrochromic inside rear view mirror, the SCM, the FCM, the EMIC, the EVIC and the left (lighting) multi-function switch. First, the Auto High Beams option must be enabled using the customer programmable features function of the EVIC. Then the A (Automatic) position must be selected using the left multi-function switch, the headlamp beam selector switch must be in the high beam position and the appropriate ambient light conditions must be present. Finally, the vehicle speed must be greater than 32 kilometers-per-hour (20 miles-per-hour).

Once all of these prerequisites have been met, the SmartBeam(R) camera and its circuitry within the electrochromic mirror automatically sends the appropriate electronic headlamp beam select switch status messages to the FCM over the CAN data bus. The FCM then responds to these messages by providing a pulse width modulated voltage output to the proper headlamp bulbs through the right and left low and high beam feed circuits to illuminate the headlamps. The FCM also sends the appropriate electronic messages back to the EMIC to control the illumination of the high beam indicator.

The SCM continues to monitor the left multi-function switch, and will send the appropriate electronic messages to the EMIC, which relays these messages to the SmartBeam(R) circuitry in the inside rear view mirror and to the FCM to manually invoke the beam select switch momentary optical horn (flash-to-pass) feature or, when a detent switch position is selected to override SmartBeam(R) operation.

TRAILER TOW WIRING

In addition to the trailer tow wiring provisions, domestic market vehicles equipped with an optional trailer tow package include right and left trailer tow stop/turn relays installed in the IPM. When the FCM receives the appropriate inputs for normal turn signal, hazard warning or brake lamp operation, it responds by also energizing or de-energizing these trailer tow relays. When a trailer tow relay is energized, it provides battery voltage from a fused B(+) fuse to the trailer lamps through the trailer tow wiring to synchronize the illumination and flash rate of the trailer brake and turn signal lamps with those of the tow vehicle.

In certain export markets, instead of trailer tow relays vehicles equipped with a factory-installed trailer towing package have a Trailer Module (TM). The TM provides the appropriate outputs to the trailer electrical system through the trailer tow connector based upon both hard wired inputs from the vehicle electrical system and messages received from the FCM over the CAN data bus. The TM also monitors the condition of the trailer lighting through circuit resistance and provides both visual and audible feedback to the vehicle operator by sending messages back to the FCM which increase turn signal flash and click rates when a problem is detected. The TM messages the FCM when the trailer wiring is connected, then the FCM suppresses operation of the rear fog lamps on the vehicle while the TM implements operation of the rear fog lamps on the trailer.

TURN SIGNAL LAMPS

The turn signal lamps system includes the SCM, the EMIC, the FCM and the left (lighting) multi-function switch on the steering column. The front turn signal lamp bulbs each have a path to ground at all times through their connection to the headlamp and dash wire harness. The headlamp and dash wire harness has takeouts with eyelet terminals that are secured by ground screws to the body sheet metal within the engine compartment. The rear turn signal lamp bulbs have a path to ground at all times through a takeout and eyelet terminal of the body wire harness that is secured by a ground screw to the body sheet metal within the passenger compartment.

The SCM monitors a hard wired multiplex input from the left multi-function switch to determine the status of the turn signal switch, then sends the appropriate electronic turn signal switch status messages to the EMIC over the LIN data bus. Then the EMIC relays an electronic turn signal request message to the FCM over the CAN data bus. The FCM responds to these messages by controlling a battery voltage output and the flash rate for either the right or left turn signal lamps. The FCM also sends the appropriate electronic messages back to the EMIC to control the illumination and flash rate of the right or left turn signal indicators, as well as to control the click rate of an electromechanical relay soldered onto the EMIC electronic circuit board that emulates the sound emitted by a conventional turn signal flasher.

The EMIC also provides a turn signal ON warning that will generate repetitive chimes to indicate that a turn signal has been active continuously for 1.6 kilometers (1 mile) with the vehicle speed greater than 22 kilometers-per-hour (15 miles-per hour). Vehicles built for markets other than the United States and Canada have a revised distance threshold of 4 kilometers (2.49 miles) for this feature. The chime will continue until the turn signal input becomes inactive or until the vehicle speed message indicates that the speed is less than 22 kilometers-per-hour (15 miles-per-hour), whichever occurs first.