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.

ADAPTIVE FRONT LIGHTING SYSTEM

The Adaptive Front Lighting System (AFLS) module monitors hard wired inputs from the front and rear axle (leveling) sensors. The AFLS module also monitors electronic message inputs from the Body Control Module (BCM) (also known as the Common Body Controller/CBC), the Controller Antilock Brake (CAB) (also known as the Antilock Brake Module/ABM, Antilock Brake System/ABS module or the Electronic Stability Control/ESC module) the Powertrain Control Module (PCM), the Steering Angle Sensor (SAS) and the Steering Control Module (SCM) received over the Controller Area Network (CAN) data bus.

The AFLS module is programmed to use these inputs and, as a Local Interface Network (LIN) master node, respond by providing electronic message outputs over a Local Interface Network (LIN) data bus connection to the leveling and swiveling stepper motors within each High Intensity Discharge (HID) front lamp unit. The four stepper motors, which are each a LIN slave node, respond by adjusting the aim of the headlamp beams up, down, right or left as commanded. The stepper motors then provide a confirmation reply over the LIN bus to the AFLS module indicating the current beam position.

AUTOMATIC HEADLAMPS

The automatic headlamp system includes the headlamp switch, the Body Control Module (BCM) (also known as the Common Body Controller/CBC), the air conditioner - heater control unit and the sun load sensor on the top of the instrument panel.

The sun load sensor provides an ambient light level input to the A/C - heater control whenever the ignition switch is in the ON position. The A/C - heater control responds to this input by sending the appropriate electronic light level messages to the BCM over the Controller Area Network (CAN) data bus. When the AUTO (Automatic) position is selected with the headlamp switch, the BCM receives a hard wired multiplex input from the headlamp switch. The BCM also receives electronic messages over the CAN data bus from the PCM indicating the engine is running.

The BCM responds to these input conditions by automatically controlling a Pulse-Width Modulated (PWM) voltage output to the selected headlamp bulbs or lighting elements through the right and left low or high beam driver circuits to illuminate the headlamps. The BCM 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 to the body sheet metal within the passenger compartment. The Powertrain Control Module (PCM) continually monitors a hard wired multiplex input from the Transmission Range Sensor (TRS), then sends the appropriate 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 Body Control Module (BCM) (also known as the Common Body Controller/CBC) 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 control output 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 Controller Antilock Brake (CAB) (also known as the Antilock Brake Module/ABM, the Antilock Brake System/ABS module or the Electronic Stability Control/ESC module) monitors a hard wired input from the brake pedal position sensor, which is actuated by movement of the brake pedal arm. When the CAB receives an input from the brake pedal position sensor indicating movement of the brake pedal arm, it responds by sending the appropriate electronic brake lamp switch status message to the BCM over the CAN data bus. The BCM then controls brake lamp and CHMSL illumination through High Side Drivers (HSD) on the left and right stop lamp control circuits. The brake lamp function of the trailer tow wiring is also controlled by an output from the BCM based upon the electronic brake lamp switch status messages received from the CAB.

DAYTIME RUNNING LAMPS

Vehicles equipped with this option or manufactured for sale in Canada illuminate multiple Light-Emitting Diode (LED) units in both front lamp units when the engine is running, the parking brake is released and the exterior lamps are turned OFF. The BCM must be programmed appropriately for this feature to be enabled. Once enabled, anytime the BCM receives electronic messages over the CAN data bus from the PCM indicating the engine is running, a hard wired multiplex input from the headlamp switch indicating the status of the headlamp switch is OFF and a hard wired input from the park brake switch indicating that the parking brake is released, the BCM provides an output to the appropriate LED units to produce illumination. If a turn signal is activated while the DRL units are active, the DRL for the same side of the vehicle as the indicated turn is extinguished until the turn signal is cancelled to permit clear signal visibility.

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 headlamp and dash wire harness and a takeout with an eyelet terminal that is secured to the body sheet metal. The BCM monitors a hard wired multiplex input from the headlamp switch to determine whether the fog lamps are selected.

When the BCM input from the headlamp switch indicates the fog lamps are selected, it 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 BCM also sends the appropriate electronic messages to the Instrument Cluster (IC) (also known as the Common Instrument Cluster/CIC) to illuminate or extinguish the front fog lamp indicator. The BCM will automatically de-energize the front fog lamps any time the headlamp high beams are selected, except on vehicles manufactured for certain export markets.

The BCM 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, 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 IC, the BCM and the hazard switch in the instrument panel switch bank of the Integrated Center Stack (ICS) module located in the center stack area of the instrument panel. The hazard switch provides a hard wired input to the BCM. When the BCM 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 control circuits.

The BCM also sends the appropriate electronic messages to the IC 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 IC electronic circuit board that emulates the sound emitted by a conventional electromechanical hazard warning flasher.

HEADLAMPS

The headlamp system includes the IC, the BCM, the headlamp switch on the instrument panel, the Steering Column Module (SCM) and the multi-function switch on the steering column. The headlamp bulbs 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 to the body sheet metal. The BCM will store a Diagnostic Trouble Code (DTC) for any shorts or opens in the headlamp circuits.

The BCM monitors a hard wired multiplex input to determine the status of the headlamp switch on the instrument panel, while the SCM monitors a hard wired multiplex input from the multi-function switch to determine whether the headlamp high or low beams are selected. The SCM sends the appropriate headlamp beam select switch status messages to the BCM over the CAN data bus. The BCM responds to these input conditions by controlling an output to the headlamp shutter solenoid to activate the appropriate headlamp beam output level. The BCM also sends the appropriate electronic messages to the IC to control the illumination of the high beam indicator.

When the optical horn feature is selected, the low beams will shut OFF about 200 milliseconds after the high beams are activated. The BCM 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 BCM 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 provides a fail-safe feature for the headlamps, which will cause the BCM to turn the low beam headlamps ON automatically if there is no input available from the multi-function switch. The BCM provides a fail-safe feature for the headlamps, which will turn the low beam headlamps ON automatically if there is no input available from the headlamp switch. The BCM 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 integral adjustment screws to be used for static aiming of the headlamps.

HEADLAMP TIME DELAY

The headlamp time delay feature includes the headlamp switch and the BCM. This feature is customer programmable using the Electronic Vehicle Information Center (EVIC) switches and the U-Connect Touch(TM) screen module in the Integrated Center Stack (ICS). If the headlamp switch is in the AUTO (Automatic) position when the ignition switch is moved from the ON position to any position except ON, then the headlamps will remain illuminated until after the selected delay interval has elapsed. The park lamps will not stay ON during the headlamp time delay interval. The default delay interval is 90 seconds, but can be reprogrammed by the customer using the EVIC switches.

MIRROR APPROACH LAMPS

The approach lamps integral to the outside rear view mirrors on vehicles equipped with the Passive Entry (PE) system are controlled by the interior courtesy lamp circuit. Interior Lighting - Operation.

MIRROR SIGNAL LAMPS

The signal lamps integral to the outside rear view mirrors on vehicles so equipped are controlled by the turn signal circuits.

PARK LAMPS

The park lamps system includes the headlamp switch on the instrument panel and the BCM. The front park lamp bulbs and LED unit marker lamps 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 to the body sheet metal. The rear park/tail lamp and side marker LED units and the license plate lamp bulbs 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 BCM monitors a hard wired multiplex input from the headlamp switch. The BCM responds to this input by controlling a battery voltage output to the appropriate lamps and bulbs through high side drivers on the front and rear, right and left lamp driver and control circuits.

The BCM 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 BCM also provides a fail-safe feature for the park lamps, which will turn the park lamps and low beam headlamps ON automatically if there is no input available from the headlamp switch. The BCM also provides a fail-safe feature for the park lamps that will turn the park lamps and low beam headlamps ON automatically whenever a loss of CAN bus communication is detected with the ignition switch in the ON 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 SCM, the BCM, the IC, 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 AUTO (Automatic) position must be selected using the rotary knob of 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 mirror automatically sends the appropriate electronic headlamp beam select switch status messages to the BCM over the Local Interface Network (LIN) data bus. The BCM then responds to these messages by providing an output to the headlamp bulbs or the lighting elements through the right and left low and high beam feed circuits to illuminate the headlamps. The BCM also sends the appropriate electronic messages back to the IC 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 BCM, which relays these messages to the SmartBeam(R) circuitry in the inside rear view mirror 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 IC and the BCM. 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 to the body sheet metal. The rear turn signal LED units 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 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 BCM over the CAN data bus. The BCM 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 control circuits. The BCM also sends the appropriate electronic messages to the IC 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 IC electronic circuit board that emulates the sound emitted by a conventional electromechanical turn signal flasher.

The BCM also provides a Turn Signal ON warning that will send a turn signal ON warning request message to the IC over the CAN bus that causes the IC to 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). 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.