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 rear lighting wire harness that is secured by a ground screw to the base of the right D-pillar behind the quarter trim panel. The backup lamps receive battery voltage from a fused ignition switch output (run) fuse on the back-up lamp feed circuit only when the backup lamp switch (manual transmission) or the Transmission Range Sensor (TRS - electronic automatic transmission) is closed by the gearshift mechanism within the transmission.

BRAKE LAMPS

The brake (or stop) lamps have a path to ground at all times through the rear lighting harness and a takeout and eyelet terminal of the rear body wire harness that is secured by a ground screw at the base of the right D-pillar behind the quarter trim panel. The Center High Mounted Stop Lamp (CHMSL) has a path to ground at all times through a takeout and eyelet terminal of the rear body wire harness that is secured by a ground screw at the base of the driver side (left or right) D-pillar behind the quarter trim panel. The brake lamps and CHMSL receive battery voltage from a fuse in the Junction Block (JB) on the brake lamp switch output circuit when the brake lamp switch is closed by the brake pedal arm.

DAYTIME RUNNING LAMPS

Vehicles equipped with this option illuminate the high beam filament of both headlamp bulbs at a reduced intensity when the engine is running and the exterior lamps are turned off. This feature is enabled by the Body Control Module (BCM) and a solid state Daytime Running Lamps (DRL) relay, which is installed in the Junction Block (JB). The high beam relay is omitted from the JB on vehicles equipped with DRL.

When the BCM monitors an electronic engine speed message of greater than 450 rpm and the status of the exterior lighting switch input is OFF, the BCM duty cycles the DRL relay to produce illumination of the headlamp high beam filaments at a reduced intensity. The BCM also provides normal headlamp high beam operation through the DRL relay on vehicles so equipped. When the DRL relay is energized, it provides battery voltage from a fused B(+) fuse in the JB to the headlamp high beam filament through the DRL relay output circuit.

FRONT FOG LAMPS

Vehicles equipped with optional front fog lamps have a premium Body Control Module (BCM), a front fog lamp relay installed in the Junction Block (JB), and a front fog lamp switch integral to the left control stalk of the multi-function switch. The front fog lamps have a path to ground at all times through their connection to the front fascia wire harness from two take outs with eyelet terminals that are secured by ground screws to the left inner fender shield in the engine compartment.

The BCM controls front fog lamp operation by monitoring the exterior lighting switch input from the multi-function switch, then energizing or de-energizing the front fog lamp relay control coil. The BCM also sends the appropriate electronic message to the ElectroMechanical Instrument Cluster (EMIC) over the Programmable Communications Interface (PCI) data bus to control operation of the front fog lamp indicator.

When the front fog lamp relay is energized, it provides battery voltage from a fused B(+) fuse in the JB to the front fog lamps through the front fog lamp relay output circuit. The BCM 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 OFF position. In certain markets where required, the front fog lamps are also turned OFF by the BCM whenever 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

With the hazard switch in the ON position, the hazard warning system is activated causing the hazard switch button, the right and left turn signal indicators, and the right and left turn signal lamps to begin flashing ON and OFF. When the hazard warning system is activated, the circuitry within the hazard switch and electronic combination flasher unit will repeatedly energize and de-energize two internal relays that switch battery voltage from a fused B(+) fuse in the Junction Block (JB) to the turn signal indicators and the turn signal lamps through the right and left turn signal circuits.

The flashing of the hazard switch button illumination lamp is performed internally by the hazard switch and combination flasher unit circuit board. The hazard warning lamps can also be energized by the Body Control Module (BCM) through a hazard lamp control circuit input to the hazard switch and combination flasher unit.

HEADLAMPS

The headlamp system includes the Body Control Module (BCM), a low beam relay installed in the Junction Block (JB), a high beam relay installed in the JB (except vehicles equipped with the optional Daytime Running Lamps/DRL), a solid state Daytime Running Lamps (DRL) relay installed in the JB (vehicles equipped with DRL only), the exterior lighting switches integral to the left (lighting) control stalk of the multi-function switch, and the ElectroMechanical Instrument Cluster (EMIC). The headlamps have a path to ground at all times through the grille opening reinforcement wire harness and two take outs with eyelet terminals of the headlamp and dash wire harness that are secured by ground screws to the left inner fender shield in the engine compartment.

The BCM controls headlamp operation by monitoring the exterior lighting switch inputs from the multi-function switch, then energizing or de-energizing the low beam relay, the high beam relay or the solid state circuitry of the DRL relay. It also sends electronic messages to the EMIC over the Programmable Communications Interface (PCI) data bus to control operation of the high beam indicator. When each respective relay is energized, it provides battery voltage from a fuse in the Power Distribution Center (PDC) through a relay (low beam, high beam, or DRL) output circuit.

The BCM also 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 OFF position; and, a headlamp DELAY feature with optional delay intervals that can be programmed using a diagnostic scan tool. Each headlamp includes an integral reflector adjustment screw to be used for static aiming of the headlamp beams.

HEADLAMP LEVELING

In certain markets where required, a headlamp leveling system is provided on the vehicle. The headlamp leveling system includes unique headlamp units equipped with a headlamp leveling actuator motor, and a rotary thumbwheel-actuated headlamp leveling switch on the instrument panel. The 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. The headlamp leveling switch is a resistor multiplexed unit that provides one of four voltage outputs to the headlamp leveling motors. The headlamp leveling motors will move the headlamps to the selected position based upon the voltage input received from the switch. The headlamp leveling motors and switch have a path to ground at all times. The headlamp leveling components operate on battery voltage received through the fused park lamp relay output circuit so that the system will only operate when the exterior lighting is turned ON.

LIGHT BAR LAMPS

The optional light bar (auxiliary off-road) lamps system includes the Body Control Module (BCM), the light bar switch on the instrument panel, and the ElectroMechanical Instrument Cluster. For all North American markets, the light bar switch receives battery voltage on a fused ignition switch output (run-start) circuit, which enables the switch to energize the lamps whenever the ignition switch is in the ON or START positions. For markets outside of North America, the light bar switch receives battery voltage from the park lamp relay in the Junction Block (JB) on the park lamp relay output circuit, and monitors an input from the low beam driver output circuit of the low beam relay in the JB, which enables the switch to energize the light bar lamps only with the park lamps ON and the low beam headlamps OFF.

The light bar lamps have a path to ground at all times through a take out and eyelet terminal of the instrument panel wire harness that is secured by a nut to a ground stud on the left instrument panel end bracket (left-hand drive) or the center of the instrument panel support structure (right-hand drive). The light bar switch controls light bar lamp operation by providing battery voltage from a fused B(+) fuse in the Power Distribution Center (PDC) to the lamps on the lightbar switch output circuit. When the lightbar switch output circuit is energized, the light bar switch also provides an input to the BCM on the lightbar switch sense circuit. The BCM then provides the appropriate electronic messages to the EMIC over the Programmable Communications Interface (PCI) data bus to control operation of the light bar indicator, the high beam indicator, or both indicators as required by the market for which the vehicle was manufactured.

PARK LAMPS

The park lamps system includes the Body Control Module (BCM), a park lamp relay installed in the Junction Block (JB), and the exterior lighting switch integral to the left (lighting) control stalk of the multi-function switch. The front park lamp and side marker lamp or, if equipped, the front position lamp bulbs each have a path to ground at all times through two take outs with eyelet terminals of the headlamp and dash wire harness that are secured by ground screws to the left inner fender shield in the engine compartment. The rear park and license plate lamps have a path to ground at all times through a take out and eyelet terminal of the rear body harness that is secured by a ground screw to the base of the right D-pillar behind the quarter trim panel.

The BCM controls park lamp operation by monitoring the exterior lighting switch input from the multi-function switch, then energizing or de-energizing the park lamp relay. When the park lamp relay is energized, it provides battery voltage from a fuse in the Power Distribution Center (PDC) through a park lamp relay output circuit to the appropriate lamp bulbs. On vehicles manufactured for North American markets only, the BCM also 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 OFF position.

REAR FOG LAMPS

Rear fog lamps are installed on vehicles manufactured for certain markets where they are required. The rear fog lamp system includes a premium Body Control Module (BCM), a rear fog lamp relay installed in the Junction Block (JB), and a rear fog lamp switch integral to the left (lighting) control stalk of the multi-function switch. The rear fog lamps operate in concert with the front fog lamps. The rear fog lamps have a path to ground at all times through a take out and eyelet terminal of the rear body wire harness that is secured by a ground screw to the base of the right D-pillar behind the quarter trim panel.

The BCM controls rear fog lamp operation by monitoring the exterior lighting switch input from the multi-function switch, then energizing or de-energizing the rear fog lamp relay control coil and sending the appropriate electronic messages to the instrument cluster over the Programmable Communications Interface (PCI) data bus to control rear fog lamp indicator operation. When the rear fog lamp relay is energized, it provides battery voltage from a fused B(+) fuse in the JB to the rear fog lamps through the rear fog lamp relay output circuit. The BCM 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 OFF position.

TRAILER TOW WIRING

In addition to the trailer tow wiring provisions, vehicles equipped with an optional trailer tow package include trailer tow relays installed in a bank of connectors concealed behind the quarter trim panel above the right rear wheel house. These relays isolate the trailer lighting from the vehicle lighting and are controlled by the normal outputs of the brake lamp switch, hazard warning switch/combination flasher unit, and the park lamp relay. 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, park and turn signal lamps with those of the tow vehicle.

TURN SIGNAL LAMPS

When the left control stalk of the multi-function switch is moved up (right turn) or down (left turn), the turn signal system is activated causing the selected right or left turn signal indicators and turn signal lamps to flash ON and OFF. When the turn signal system is activated, the circuitry within the turn signal switch and the hazard switch/electronic combination flasher unit will repeatedly energize and de-energize one of two internal relays that switch battery voltage from a fused ignition switch output (run) fuse in the Junction Block (JB) to the appropriate turn signal indicator and turn signal lamps.

The ElectroMechanical Instrument Cluster (EMIC) chime tone transducer will generate an audible turn signal cancel warning each time the vehicle is driven for a distance of about 3.2 kilometers (about 2 miles) with a turn signal indicator flashing. The EMIC uses electronic distance messages received over the Programmable Communications Interface (PCI) data bus from the Powertrain Control Module (PCM) and a hard wired input from the turn signal switch circuitry or the multi-function switch to determine when to sound the turn signal cancel warning.