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.

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. On vehicles with a manual transmission, when REVERSE is selected, the backup lamp switch provides a hard wired input to the Powertrain Control Module (PCM) through a reverse switch signal circuit. The PCM then sends an electronic reverse transmission gear selector status message to the Body Control Module (BCM) over the Controller Area Network (CAN) data bus. The BCM energizes a high side driver which provides battery voltage to the backup lamps on the backup lamp feed circuit whenever the ignition switch is in the ON position and the REVERSE position is selected with the transmission shift linkage.

On vehicles with an automatic transmission, the Transmission Control Module (TCM) monitors a multiplex input from the Transmission Range Sensor (TRS). When REVERSE is selected, the TCM sends an electronic reverse transmission gear selector status message to other electronic modules over the CAN data bus. Whenever the ignition switch is in the ON position and the BCM receives an electronic message indicating the status of the transmission gear selector is REVERSE, the BCM energizes a high side driver, which provides battery voltage 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 screw to the body sheet metal. The BCM receives a battery voltage input whenever the brake lamp switch is closed by the brake pedal arm. The BCM then energizes a high side driver, which provides battery voltage to the brake lamps and the CHMSL through a tail/stop lamp rear feed circuits.

DAYTIME RUNNING LAMPS

Vehicles with the Daytime Running Lamps (DRL) feature enabled illuminate the clearance (position) lamp bulbs in the upper cavity of the two lower front combination lamp units when the engine is running, the parking brake is released, the headlamps are turned OFF, and the optional automatic transmission gear selector lever is in any position except PARK. The park lamps may be ON or OFF for DRL to operate. For vehicles with a manual transmission, the DRL will operate in any transmission gear selector lever position. The BCM must be programmed appropriately for this feature to be enabled.

Once enabled, anytime the BCM receives an electronic message input over the CAN data bus from the PCM indicating the engine is running, hard wired inputs indicating the left (lighting) multi-function switch is in any position except headlamps ON and the parking brake lever is released, and from the TCM indicating the automatic transmission gear selector lever is in any position except PARK, the BCM energizes a high side driver, which provides battery voltage to the clearance lamp bulbs through the right and left clearance lamp feed circuits.

FRONT FOG LAMPS

The front fog lamps have a path to ground at all times through their connection to the headlamp and dash wire harness. The engine compartment wire harness has takeouts with eyelet terminals that are secured by screws to the front end sheet metal within the engine compartment. The BCM monitors a hard wired input from the fog lamp switch in the lower instrument panel switch pod to determine whether the front fog lamps are selected. If the front fog lamps are selected and the left (lighting) multi-function switch inputs indicate the headlamp low beams are ON, the BCM energizes a high side driver, which provides battery voltage to the front fog lamps through the right and left front fog lamp feed circuits.

The BCM also sends the appropriate electronic messages to the Instrument Panel Cluster (IPC) over the CAN data bus to illuminate or extinguish the front fog lamp indicator. The BCM will automatically de-energize the front fog lamps any time the headlamps are turned OFF or the headlamp high beams are selected.

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

HAZARD WARNING LAMPS

The BCM monitors a hard wired input from the hazard switch in the lower instrument panel switch pod located in the center of the air conditioner and heater control head to determine whether the hazard warning system has been selected. When the hazard warning system is selected, the BCM controls hazard warning system operation and flash rate by energizing and de-energizing high side drivers, which controls battery voltage outputs on the right and left turn signal feed circuits. The BCM also sends electronic hazard switch status messages to the IPC over the CAN data bus to control the illumination and flash rate of the left and right turn signal indicators, as well as to control the click rate of an electromechanical relay soldered onto the IPC electronic circuit board that emulates the sound emitted by a conventional hazard warning flasher.

HEADLAMPS

The headlamp system includes the BCM, the IPC and the left (lighting) 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 by screws to the front end sheet metal within the engine compartment. The BCM monitors hard wired inputs to determine the status of the left multi-function switch and whether the headlamp high or low beams are selected. The BCM then controls headlamp illumination through relays soldered onto the BCM internal circuit board.

On vehicles manufactured for the U.S. or Canada when the BCM detects a change in headlamp beam selection, the BCM energizes or de-energizes a high side driver, which controls an output to the solenoid that operates the shutter in each headlamp. The BCM also sends the appropriate electronic messages to the IPC to control the illumination of the high beam indicator. The BCM 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.

On vehicles manufactured for the U.S. or Canada each headlamp includes an integral reflector adjustment screw to be used for static aiming of the headlamps. On vehicles manufactured for Mexico or Latin America each upper front combination lamp unit includes two integral reflector adjustment screws, while each lower front combination lamp unit includes one integral reflector adjustment screw to be used for static aiming of the headlamp beams.

HEADLAMP DELAY

The headlamp delay feature (also known as the Follow Me Home feature) includes the left (lighting) multi-function switch, the IPC and the BCM. The BCM controls this feature by monitoring inputs from the ignition switch and the left (lighting) multi-function switch. If within two minutes after the ignition switch is turned to the OFF position, the left multi-function switch control stalk is pulled toward the steering wheel and released the BCM energizes the relay that controls the headlamp low beams and the high side driver that controls the clearance (position) lamps for 30 seconds. Each additional activation of the control stalk extends the delay by 30 seconds, up to a maximum of 210 seconds. The BCM automatically de-energizes the lamps after the selected time interval expires or, immediately, if the control stalk is pulled toward the steering wheel and held for more than two seconds. The BCM also sends the appropriate electronic messages to the IPC over the CAN data bus to control the Follow Me Home indications in the IPC display.

HEADLAMP LEVELING

In vehicles manufactured for Mexico and Latin America a headlamp leveling system is provided on the vehicle. The headlamp leveling system includes unique upper front combination lamp units each with an integral headlamp leveling actuator motor, and push button headlamp leveling switches integral to the IPC in the instrument panel. The headlamp leveling system allows the headlamp low 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 a headlamp leveling switch push button is depressed the circuitry of the switch provides an up or down input to the IPC. The IPC then provides a voltage output to the electronic controller integral to each headlamp leveling motor. The electronic controller of the headlamp leveling motors move the headlamp reflectors to the selected position based upon the voltage input received from the IPC. The headlamp leveling motors send the appropriate information back to the IPC and the IPC displays the 0, 1, 2 or 3 to indicate the selected position in the IPC display. The system logic will only allow the headlamp leveling system to operate while the ignition switch is in the ON position and the low beam headlamps are turned ON.

PARK LAMPS

The park lamps system includes the left (lighting) multi-function switch, the IPC and the BCM. The clearance (position) lamp bulbs in the upper cavity of each lower front combination lamp unit 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 screws to the front end sheet metal within the engine compartment. The park (tail) lamp bulbs in each rear lamp unit and the license plate 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 screw to the body sheet metal within the passenger compartment.

The BCM monitors a hard wired input from the left (lighting) multi-function switch, then responds to this input by energizing or de-energizing high side drivers, which control battery voltage outputs to the appropriate lamps and bulbs through the proper park/tail/license/running lamp right and left circuits. The BCM also provides the appropriate electronic messages to the IPC to control the illumination and lighting level of the panel lamps.

REAR FOG LAMP

The rear fog lamp has a path to ground at all times through a connection to the body wire harness. The body wire harness has takeouts with eyelet terminals that are secured by screws to the body sheet metal within the passenger compartment. The BCM monitors a hard wired input from the fog lamp switch in the lower instrument panel switch pod to determine whether the rear fog lamp is selected. If the rear fog lamp is selected the BCM energizes a relay in the Power Distribution Center (PDC) with a low side driver, which provides battery voltage to the rear fog lamp through the rear fog lamp feed circuit.

The BCM also sends the appropriate electronic messages to the Instrument Panel Cluster (IPC) over the CAN data bus to illuminate or extinguish the rear fog lamp indicator.

TURN SIGNAL LAMPS

The turn signal lamps system includes the left (lighting) multi-function switch, the IPC and the BCM. The front turn signal lamp bulbs in the lower cavity of each lower front combination lamp unit (U.S. or Canada) or in the upper cavity of each upper front combination lamp unit (Mexico or Latin America) and the repeater 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 a takeout with an eyelet terminal that is secured by a screw 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 screw to the body sheet metal within the passenger compartment.

The BCM monitors a hard wired input from the left (lighting) multi-function switch to determine the status of the turn signal switch, then controls turn signal operation and flash rate by energizing and de-energizing high side drivers, which control battery voltage outputs on the right or left turn signal feed circuits. The BCM also sends electronic turn signal switch status messages to the IPC over the CAN data bus to control the illumination and flash rate of the left or right turn signal indicators, as well as to control the click rate of an electromechanical relay soldered onto the IPC electronic circuit board that emulates the sound emitted by a conventional turn signal flasher.