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 headlamp switch on the instrument panel, the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN), the Totally Integrated Power Module (TIPM), the ignition switch (also known as the Wireless Ignition Node/WIN), the heater and air conditioner control unit and the sun load sensor on the top of the instrument panel.

The TIPM energizes the sun load sensor to provide an ambient light level input to the A/C - heater control whenever the electronic ignition switch status messages received from the WIN over the Controller Area Network (CAN) data bus indicate the ignition ON position is selected. The A/C - heater control responds to the sun sensor input by sending the appropriate electronic light level messages back to the TIPM over the CAN data bus. When the A (Automatic) position is selected with the headlamp switch, the EMIC responds to this input by sending electronic lighting request messages to the TIPM over the CAN data bus.

With the engine running, the TIPM responds to these messages by automatically controlling a pulse width modulated voltage output to the selected headlamp bulb filaments through the right and left low or high beam driver circuits to illuminate the headlamps. The TIPM also remembers which beams (low or high) were selected when the headlamps were last turned OFF, and energizes those beams and lamps again the next time it turns the headlamps ON.

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 the body sheet metal. The Powertrain Control Module (PCM) 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 electronic ignition switch status messages indicate the ignition ON position is selected and the TIPM 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. The TIPM and the CHMSL receive battery voltage on the brake lamp switch feed circuit when the brake lamp switch is closed by the brake pedal arm. The brake lamps are then controlled by the TIPM through High Side Drivers (HSD) on the left and right rear turn driver circuits. The brake lamp function of the optional trailer tow wiring is also controlled by an output from the TIPM based upon a hard wired input from the brake lamp switch.

DAYTIME RUNNING LAMPS

Vehicles equipped with this option or manufactured for sale in Canada illuminate the high beam filament of both headlamps at a reduced intensity when the engine is running, the parking brake is released and the exterior lamps are turned OFF. The TIPM must be programmed appropriately for this feature to be enabled. Once enabled, anytime the TIPM receives electronic messages over the CAN data bus from the PCM indicating the engine is running and from the EMIC indicating the status of the headlamp switch exterior lighting input is OFF and that the parking brake is released, the TIPM provides a pulse width modulated voltage output to the proper headlamp 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 switch integral to the headlamp switch on the instrument panel. The front fog lamps have a path to ground at all times through their connection to the Front End Module (FEM) wire harness. The FEM wire harness has takeouts with eyelet terminals that are secured by ground screws to the body sheet metal within the engine compartment. The EMIC monitors a hard wired multiplex input from the headlamp switch to determine whether the fog lamps are selected, then sends electronic fog lamp switch request messages to the TIPM over the CAN data bus.

When the TIPM receives a fog lamp switch request message it then controls front fog lamp operation by providing a battery voltage output to the fog lamps through the right and left front fog lamp control circuits. The TIPM also sends the appropriate electronic message back to the EMIC to illuminate or extinguish the front fog lamp indicator. The TIPM will automatically de-energize the front fog lamps any time the headlamp high beams are selected.

The TIPM 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 after the electronic ignition switch status messages from the WIN transitions to LOCK, if there is a charging system failure or if the electrical system voltage falls below about 11.75 volts for more than about 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 TIPM and the hazard switch in the switch pod located in the center stack area of the instrument panel. The hazard switch provides a hard wired input to the TIPM. When the TIPM receives an input from the hazard switch it controls hazard warning system operation and flash rate by controlling battery voltage outputs through high side drivers on the front and rear, right and left turn signal feed circuits.

The TIPM 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.

HEADLAMPS

The headlamp system includes the SCM, the EMIC, the TIPM, the headlamp switch on the instrument panel and the multi-function switch on the steering column. On vehicles with the optional High Intensity Discharge (HID) headlamps, the HID electronic ballast module of each front lamp unit is also part of the headlamp system. Each halogen headlamp bulb and the HID electronic ballast module has a path to ground at all times through their connection to the FEM wire harness. The FEM wire harness has takeouts with eyelet terminals that are secured by ground screws to the body sheet metal within the engine compartment. The TIPM will store a Diagnostic Trouble Code (DTC) for any shorts or opens in the headlamp circuits.

The EMIC monitors a hard wired multiplex input from the headlamp switch to determine the status of the headlamp switch. The SCM monitors a hard wired multiplex input to determine the status of the multi-function switch and whether the headlamp high or low beams are selected. The SCM then sends the appropriate electronic headlamp beam select switch status messages to the EMIC over the Local Interface Network (LIN) data bus. The EMIC then sends the appropriate electronic headlamp request and headlamp beam request messages to the TIPM over the CAN data bus. The TIPM responds to these messages by providing a Pulse Width Modulated (PWM) voltage output to the proper halogen headlamp bulbs or a control voltage to the HID electronic ballast modules through high side drivers on the right and left low and high beam feed circuits to illuminate the selected headlamp beams. The TIPM also sends the appropriate electronic messages back to the EMIC to control the illumination of the high beam indicator.

On vehicles with the optional HID headlamps, the HID electronic ballast module uses a high voltage Alternating Current (AC) output to activate the HID igniter integral to the lighting element to provide a high voltage surge, which creates a light arc between the lighting element electrodes. Once the electronic ballast module detects a suitably stable light arc, it switches over to a power-limiting mode to sustain the light arc.

When the optical horn feature is selected, the low beams will shut OFF about 200 milliseconds after the high beams are activated. The TIPM also remembers which beams (LOW or HIGH) were selected when the headlamps were last turned OFF, and energizes those beams again the next time the headlamps are turned ON. The TIPM 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 after the electronic ignition switch status messages from the WIN transition to LOCK.

The SCM and the EMIC each provide a fail-safe feature for the headlamps, which will cause the TIPM to turn the low beam headlamps ON automatically if there is no input available from the headlamp switch or the multi-function switch. The TIPM 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 while the electronic ignition switch status messages from the WIN indicate the ignition ON position is selected.

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 headlamp switch, the EMIC, the WIN and the TIPM. On vehicles equipped with an optional Electronic Vehicle Information Center (EVIC), this feature has customer programmable delay intervals of 0 seconds (disabled), 30 seconds, 60 seconds and 90 seconds. If the headlamp switch remains in the headlamp ON position until the electronic ignition switch status messages from the WIN indicate the ignition OFF position is selected, 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 90 seconds, but can be reprogrammed by the customer using the customer programmable features function of the EVIC, if the vehicle is so equipped.

HEADLAMP LEVELING

In certain export markets where required, a manual headlamp leveling system is provided on vehicles equipped with the standard equipment quad halogen front lamp units. 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 dimmer module on Left-Hand Drive (LHD) models or a dedicated switch for Right-Hand Drive (RHD) models. On either LHD or RHD, the thumbwheel-actuated switch is located on the instrument panel between the headlamp switch and the steering column. In certain export markets where required, on vehicles with the optional equipment HID headlamps, an automatic leveling system is used that includes front and rear axle sensors and an Automatic Headlamp Leveling Module (AHLM) (also known as the High Intensity Discharge Transducer/HIDT) located on the top of the left rear wheel housing within the passenger compartment.

The manual headlamp leveling system allows the headlamp beams to be adjusted to one of three 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 three detent positions, the circuitry of the switch provides a voltage signal to the TIPM, then the TIPM responds by providing an output to both leveling actuator motors. The electronic circuitry of these stepper motors responds to the voltage inputs received from the TIPM to move the headlamp reflectors to the selected position.

The automatic headlamp leveling system automatically adjusts the headlamp beam reflectors to compensate for changes in vehicle suspension height regardless of whether caused by the loading of the vehicle suspension or vehicle pitch changes caused by acceleration and deceleration. The actuator motors are common with those in the manual system; however, rather than responding to a manual switch input, the motors are automatically adjusted by the TIPM based upon electronic messages received from the AHLM over the CAN data bus. The AHLM provides the front and rear axle sensors with voltage and ground, then reads the sensor return signals to determine the suspension height changes.

The headlamp leveling motors and switch have a path to ground at all times. Both the manual and the automatic headlamp leveling components operate on battery current received only when the exterior lighting is turned ON. In addition, on vehicles with the automatic leveling system the ignition switch must be in the ON position.

PARK LAMPS

The park lamps system includes the EMIC, the TIPM and the headlamp switch on the instrument panel. The front park lamp and side marker lamp bulbs each have a path to ground at all times through their connection to the FEM wire harness. The FEM wire harness has takeouts with eyelet terminals that are secured by ground screws to the body 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.

The EMIC monitors a hard wired multiplex input from the headlamp switch, then sends the appropriate electronic headlamp switch status messages to the TIPM over the CAN data bus. The TIPM responds to these messages by providing a battery voltage output to the appropriate lamp bulbs through high side drivers on the front and rear, right and left park lamp feed circuits.

The TIPM 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 after the electronic ignition switch status messages from the WIN indicate the ignition LOCK position is selected. The EMIC provides a fail-safe feature for the park lamps, which will send an electronic message to the TIPM to turn these lamps ON automatically if it detects no input from the headlamp switch. The TIPM also provides a fail-safe feature for the park lamps that will turn the headlamps and park lamps ON automatically whenever a loss of CAN bus communication is detected when the electronic ignition switch status messages from the WIN indicate the ignition ON position is selected.

REAR FOG LAMPS

Rear fog lamps are installed on vehicles manufactured for certain export markets where they are required. The rear fog lamp system includes the headlamp switch, the EMIC and the TIPM. The rear fog lamp bulbs have a path to ground at all times through a takeout and eyelet terminal of the body wire harness that is secured to the body sheet metal.

The EMIC monitors a hard wired multiplex input from the headlamp switch to determine whether the rear fog lamps are selected, then sends the appropriate electronic rear fog lamp request messages to the TIPM over the CAN data bus. The TIPM responds to these messages by controlling a battery voltage output to the rear fog lamp bulbs through a high side driver on the rear fog lamp signal control circuit. The TIPM also sends the appropriate electronic messages back to the EMIC to control the rear fog lamp indicator.

The TIPM will automatically energize and de-energize the front fog lamps in concert with the rear fog lamps. The TIPM 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.

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 Steering Control Module (SCM), the TIPM, the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN), the Electronic Vehicle Information Center (EVIC), the headlamp switch and the 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 headlamp 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 (EC) mirror automatically sends the appropriate electronic headlamp beam select switch status messages to the TIPM over the CAN data bus. The TIPM 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 TIPM 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 multi-function switch, and will send the appropriate electronic messages to the EMIC, which relays these messages to the SmartBeam(R) circuitry in the EC inside rear view mirror and to the TIPM 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.

TURN SIGNAL LAMPS

The turn signal lamps system includes the multi-function switch on the steering column, the SCM, the EMIC and the TIPM. The front turn signal lamp bulbs each have a path to ground at all times through their connection to the FEM wire harness. The FEM 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. On vehicles with the optional outside rear view mirror lamp modules, the lamp modules receive a path to ground from their respective driver or passenger door module.

The SCM monitors a hard wired multiplex input from the 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 TIPM over the CAN data bus. The TIPM responds to these messages by controlling a battery voltage output and the flash rate for either the right or left turn signal lamps through high side drivers on the appropriate front and rear, right or left turn signal feed circuits. The TIPM 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. On vehicles with the optional outside rear view mirror lamp modules, the EMIC also sends the appropriate electronic messages over the LIN bus to the driver and passenger door modules to control the illumination and flash rate of those lamps.

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.