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 (also known as the Rotary Lighting Switch/RLS or Light Switch Module/LSM), the Body Control Module (BCM) (also known as the Signal Acquisition and Actuation Module/SAM) and the Rain Sensor Module (RSM) (also known as the Rain/Light Sensor Module/RLSM) on the inside of the windshield below the inside rear view mirror.

First, the Auto (Automatic) position must be selected using the headlamp switch. Then the ignition switch must be in the ON position. Once these prerequisites have been met, the RSM responds by sending the appropriate electronic lighting request messages to the BCM over the Controller Area Network (CAN) data bus and the BCM responds to these messages by automatically turning the exterior lighting ON or OFF as appropriate. On vehicles with a factory-installed trailer towing package, the lighting request messages from the RSM are forwarded to the Trailer Module (TM) (also known as the trailer connection unit, Trailer Lighting Module/TLM or AAG), which automatically controls the trailer lighting circuits as appropriate.

The high or low beam headlamps are illuminated as manually selected using the control stalk of the multi-function switch (also known as the combination switch) located on the left side of the steering column. The BCM also sends the appropriate electronic messages to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN or KOMBIE) to automatically control the illumination of the high beam and low beam indicators as appropriate.

BACKUP LAMPS

The backup (or reverse) lamps have a path to ground at all times through a takeout of the vehicle wire harness that is secured to the body sheet metal. The backup lamps receive battery current from the BCM on the backup lamp supply circuit. On vehicles with a manual transmission, the BCM energizes the backup lamps only when it detects that the backup lamp switch on the transmission is a closed circuit. On vehicles with an automatic transmission, the BCM energizes the backup lamps only when it receives an electronic reverse gear ON message from the Electronic Shifter Module (ESM) (also known as the EWM) integral to the gear shifter assembly over the CAN data bus.

On vehicles with a factory-installed trailer towing package, electronic messages from the BCM over the CAN data bus are sent to the TM, which automatically controls the trailer backup lamp circuits as appropriate.

BRAKE LAMPS

The brake (or stop) lamps and, if the vehicle is so equipped, the Center High Mounted Stop Lamp (CHMSL) each have a path to ground at all times through a takeout of the vehicle wire harness that is secured to the body sheet metal. The brake lamps receive battery current from the BCM on the brake lamp switch supply circuit. The BCM energizes the brake lamps supply circuit when it receives an electronic service brake engaged message from the Controller Antilock Brake (CAB) (also known as the Antilock Brake System/ABS or Electronic Stability Program/ESP controller) over the CAN data bus, or when it detects that the brake lamp switch on the brake pedal arm is a closed circuit, whichever occurs first.

On vehicles with a factory-installed trailer towing package, electronic messages from the BCM over the CAN data bus are sent to the TM, which automatically controls the trailer brake lamp circuits as appropriate.

CORNERING ILLUMINATION

The optional xenon (also known as bi-xenon or High Intensity Discharge/HID) headlamp system includes a cornering (also known as static curve) illumination feature. This feature is delivered disabled due to regulatory requirements in some markets, but can be enabled by any dealer using a diagnostic scan tool. When cornering illumination is enabled, the xenon lamp module on each front lamp unit monitors inputs from the turn signal switch, the Steering Angle Sensor (SAS), the backup lamp switch (with manual transmission), the ESM (with automatic transmission), the headlamp switch, the RSM and the BCM.

When the vehicle is moving forward at less than about 40 kilometers-per-hour (25 miles-per-hour) with low beam headlamps turned ON (or Daytime Running Lamps/DRL active) and a turn signal is activated or a steering angle (right or left) of greater than about 40 degrees is detected, the cornering lamp on the inside of the turn is illuminated. The lamp is extinguished when the turn signal is deactivated, when the turn signal remains activated but the vehicle speed is greater than about 40 kilometers-per-hour (25 miles-per-hour) or when a steering angle of less than about 20 degrees is detected. When REVERSE gear is engaged, the cornering lamps are activated inversely.

DAYTIME RUNNING LAMPS

Vehicles manufactured for sale in Canada, or vehicles in other markets equipped with the optional steering wheel buttons and having the constant headlamp mode enabled, illuminate the low beam headlamp and the park lamp in each front lamp unit as well as the license plate lamps whenever the engine is running and the headlamp switch is in the O (Off) position to serve as the DRL. The BCM uses internal programming and monitors an input from the headlamp switch as well as electronic messages received from the Engine Control Module (ECM) (also known as the Powertrain Control Module/PCM) over the CAN data bus indicating that the engine is running to control this feature.

The BCM also sends the appropriate electronic message to the EMIC to automatically control the illumination of the low beam indicator as appropriate.

FRONT FOG LAMPS

The optional front fog lamps have a path to ground at all times through a takeout of the vehicle wire harness that is secured to the body sheet metal. The front fog lamps receive battery current from the BCM on the front fog lamp supply circuit. The BCM energizes the front fog lamps supply circuit when it receives inputs from the headlamp switch indicating the front fog lamps are selected and the park lamps or the low beam headlamps are selected. A green indicator in the headlamp switch is illuminated when the front fog lamps are turned ON. The BCM also monitors electronic beam select switch status messages received from the Steering Control Module (SCM) (also known as the steering column module/MRM) over the CAN data bus and will automatically de-energize the front fog lamps whenever the high beam headlamps are selected. The front fog lamps will not operate when the headlamp switch is in the Auto (Automatic) position.

HAZARD WARNING LAMPS

The hazard warning system includes the hazard switch integral to the instrument panel switch pod (also known as the center console switch unit, Switch Bank Module/SBM, Upper Control Panel/UCP or OBF), the EMIC and the BCM. When the hazard switch is activated, the instrument panel switch pod sends an electronic hazard switch status message to the BCM over the CAN data bus. The BCM responds by controlling the output and flash rate of all lamps in the left and right turn signal circuits, and by sending electronic messages to the EMIC and the instrument panel switch pod control the illumination and flash rate of both the turn signal indicators in the instrument cluster and the Light Emitting Diode (LED) unit behind the hazard switch push button.

On vehicles with a factory-installed trailer towing package, electronic messages from the BCM over the CAN data bus are sent to the TM, which automatically controls the trailer turn signal circuits as appropriate.

HEADLAMPS

The headlamp system includes the headlamp switch, the SCM, the BCM, the EMIC and the multi-function switch. On vehicles with the optional xenon headlamps, the xenon lamp module and electromechanical shutter mechanism of each front lamp unit are also part of the headlamp system. Each halogen headlamp bulb or xenon lamp module has a path to ground at all times through a takeout of the vehicle wire harness that is secured to the body sheet metal. The halogen headlamp bulbs receive battery current from the BCM through the right and left low and high beam feed circuits to illuminate the selected headlamp beams, while the xenon lamp module receives a control voltage from the BCM.

The BCM energizes the low or high beam feed circuits or provides a control voltage to the xenon lamp module when it receives an input from the headlamp switch indicating the headlamps are selected. The BCM also monitors electronic beam select switch status messages received from the SCM over the CAN data bus to determine the correct halogen headlamp beam circuits to energize or which beams to request from the xenon lamp module. The xenon lamp module activates the xenon ignition module integral to the lighting element to provide a high voltage surge, which creates a light arc between the lighting element electrodes. Once the lamp module detects a suitably stable light arc, it switches over to a power-limiting mode to sustain the light arc.

When the xenon lamp module detects a signal requesting a change between headlamp beams from the BCM, it actuates an electromechanical shutter mechanism within the lamp unit, which moves a shutter to either mask (low beam) or entirely expose (high beam) the light output of the xenon lighting element.

HEADLAMP LEVELING

The headlamp leveling system includes a leveling actuator motor integral to each front lamp unit. On vehicles with the standard equipment halogen headlamps, a manual leveling system is used that includes the BCM and a thumbwheel actuated headlamp leveling switch located next to the headlamp switch on the instrument panel outboard of the steering column. On vehicles with the optional equipment xenon headlamps, an automatic leveling system is used that includes front and rear axle sensors, an Automatic Headlamp Leveling Module (AHLM) (also known as the Adaptive Lighting, Headlamp Range Adjustment/HRA or LWR module) and the xenon lamp modules.

The manual headlamp leveling system allows the headlamp beam reflectors to be manually adjusted by the vehicle operator while driving to one of four vertical positions to compensate for changes in vehicle suspension height caused by the loading of the vehicle suspension. The actuator motors are mechanically connected through an integral pushrod to an adjustable headlamp reflector within each front lamp unit. The headlamp leveling switch is a resistor multiplexed unit that provides one of four voltage outputs to the BCM. The BCM reads the switch input, then provides a voltage output to the headlamp leveling motors that will move the headlamp reflector 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 AHLM, which reads the front and the rear axle sensors to determine the suspension height changes.

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 headlamp switch, the BCM, the front park/side marker lamps, the rear park/side marker lamps, the optional side marker lamps, the optional clearance lamps, the optional identification lamps and the license plate lamps. Each of these lamps are provided with a path to ground at all times through a takeout of the vehicle wire harness secured to the body sheet metal. The headlamp exterior lighting switches control the park lamp operation by providing battery current through the park lamps circuit to the appropriate lamp bulbs.

On vehicles with a factory-installed trailer towing package, electronic messages from the BCM over the CAN data bus are sent to the TM, which automatically controls the trailer park lamp circuits as appropriate.

POSITION LAMPS

The position lamps include all of the lamps in only the right side or only the left side park lamps circuits.

REAR FOG LAMP

The rear fog lamp has a path to ground at all times through a takeout of the vehicle wire harness that is secured to the body sheet metal. The rear fog lamp receives battery current from the BCM on the rear fog lamp supply circuit. The BCM energizes the rear fog lamp supply circuit when it receives inputs from the headlamp switch indicating the rear fog lamp is selected and the park lamps or the low beam headlamps are selected. An amber indicator in the headlamp switch is illuminated when the rear fog lamp is turned ON. The BCM also monitors electronic beam select switch status messages received from the SCM over the CAN data bus and will automatically de-energize the front and rear fog lamps whenever the high beam headlamps are selected. The rear fog lamp will not operate when the headlamp switch is in the Auto (Automatic) position or when the front fog lamps are turned OFF.

On vehicles with a factory-installed trailer towing package, electronic messages from the BCM over the CAN data bus are sent to the TM, which automatically controls the trailer rear fog lamp circuit as appropriate.

TRAILER TOW WIRING

In addition to the trailer tow wiring provisions, vehicles equipped with an optional trailer tow package include a Trailer Module (TM). The TM provides the appropriate outputs to the trailer electrical system through the trailer tow connector based upon electronic messages received from the BCM 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 electronic messages back to the BCM and to the EMIC which increase turn signal flash and click rates when a problem is detected. The TM also notifies other electronic modules in the vehicle when the trailer wiring is connected, which suppresses operation of certain functions and features that are incompatible with the towing of a trailer.

TURN SIGNAL LAMPS

The turn signal lamps system includes the SCM, the EMIC, the BCM and the multi-function switch on the steering column. The turn signal lamp bulbs each have a path to ground at all times through takeouts of the vehicle wire harness that are secured to the body sheet metal. The SCM monitors a hard wired 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 BCM over the CAN data bus. The BCM responds to these messages by controlling outputs and the flash rate for either the right or left turn signal lamps. The BCM also sends the appropriate electronic messages 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 a factory-installed trailer towing package, electronic messages from the BCM over the CAN data bus are sent to the TM, which automatically controls the trailer turn signal circuits as appropriate.