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. 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 left (lighting) multi-function switch, the Steering Control Module (SCM), the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN), the Totally Integrated Power Module (TIPM), the heater and air conditioner 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 TIPM over the Controller Area Network (CAN) data bus. When the AUTO (Automatic) position is selected with the left multi-function switch, the SCM responds to this input by sending the appropriate electronic lighting switch status messages to the EMIC over the Local Interface Network (LIN) data bus. The EMIC responds to this input by sending the appropriate 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 to the body sheet metal within the passenger compartment. On vehicles with a manual transmission, the backup lamp switch provides an input to the TIPM through a backup lamp switch signal circuit, and the TIPM provides battery voltage to the backup lamps on the backup lamp control output 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 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 Controller Area Network (CAN) data bus. Whenever the ignition switch is in the ON position 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 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 TIPM and the CHMSL receive battery voltage on the brake lamp switch output 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 stop lamp control circuits. A stop lamp inhibit relay (also known as a brake lamp relay, brake lamp activation relay or trailer tow damping relay) is used by the Controller Antilock Brake (CAB) to mitigate undesirable brake lamp operation when the CAB activates various brake hydraulic circuits as part of its Traction Control System (TCS) and Trailer Sway Control (TSC) functions. The brake lamp function of the 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 left multi-function switch exterior lighting switch 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 left (lighting) multi-function switch on the steering column. 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 SCM monitors a hard wired multiplex input from the left multi-function switch to determine whether the fog lamps are selected, then sends the appropriate electronic front fog lamp switch status messages to the EMIC over the LIN data bus. The EMIC then relays the appropriate electronic front fog lamp switch request messages to the TIPM over the CAN data bus.

When the TIPM receives a front fog lamp switch request message, 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 TIPM also sends the appropriate electronic messages 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, except on vehicles manufactured for certain export markets.

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 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 EMIC, the TIPM and the hazard switch in the switch pod located in the center stack area of the instrument panel, above the heater and air conditioner control unit. 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 control circuits. On vehicles manufactured for certain export markets where they are required, the TIPM provides battery voltage to the repeater lamps through right and left repeater lamp control output circuits based upon the hazard switch input.

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.

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, above the heater and air conditioner control unit. 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 control circuits. On vehicles manufactured for certain export markets where they are required, the TIPM provides battery voltage to the repeater lamps through right and left repeater lamp control output circuits based upon the hazard switch input.

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.

HEADLAMP DELAY

The headlamp delay feature includes the left (lighting) multi-function switch, the SCM, the EMIC 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 exterior lighting 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 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 headlamp leveling system is provided on the vehicle. The headlamp leveling system includes unique front lamp units each equipped with a headlamp leveling actuator motor, and a rocker-actuated headlamp leveling switch integral to the switch pod in the instrument panel center stack. 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.

Each time the headlamp leveling switch is depressed the circuitry of the switch pod provides the appropriate electronic select status up or select status down messages to the EMIC over the LIN data bus. The EMIC then sends the appropriate electronic select request up or select request down messages to the TIPM over the CAN data bus. The TIPM responds to these messages by providing a voltage output to the headlamp leveling motors through a high side driver on the headlamp level sensor signal circuit to move the headlamp reflectors to the selected position based upon the voltage input received from the TIPM. The TIPM also sends the appropriate electronic messages back to the EMIC and the EMIC relays the messages back to the switch to control the illumination of the 1 , 2 , or 3 Light Emitting Diode (LED) selected position indicator in the headlamp leveling switch button.

The EMIC and TIPM logic will only allow the headlamp leveling system to operate while the ignition switch is in the ON position and the exterior lighting is turned ON.

PARK LAMPS

The park lamps system includes the left multi-function switch on the steering column, the SCM, the EMIC and the TIPM. The front park lamp, side marker lamp and, on vehicles manufactured for certain export markets, position 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 park/tail lamp, side marker lamp and 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 SCM monitors a hard wired multiplex input from the exterior lighting switch of the left multi-function switch, then sends the appropriate electronic lighting switch status messages to the EMIC over the LIN data bus. The EMIC then relays the appropriate electronic lighting request 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 lamp driver and control 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 with the ignition switch in the LOCK position. The SCM and the EMIC each provide a fail-safe feature for the park lamps, which will cause the TIPM to turn the park lamps and low beam headlamps ON automatically if there is no input available from the SCM or the left multifunction switch. The TIPM 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.

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 left (lighting) multi-function switch, the SCM, 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 SCM monitors a hard wired multiplex input from the left multi-function switch to determine whether the rear fog lamps are selected, then sends the appropriate electronic rear fog lamp switch status messages to the EMIC over the LIN data bus. Then the EMIC relays 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.

TRAILER TOW WIRING

Vehicles equipped with an optional trailer tow preparation package are shipped from the factory with a trailer tow wiring harness and 4-pin trailer connector that is packaged with an instruction card and placed in the glove box of the vehicle. The trailer tow harness includes four relays designed to isolate the trailer turn signal and stop lamp lighting from the rear vehicle lighting and prevent overloading of the turn signal and stop lamp lighting drivers in the TIPM. These vehicles also include a dedicated park lamp control output circuit protected by a 15 ampere fuse located in the TIPM.

If the trailer lighting is connected directly to the vehicle wiring without using the necessary relays, the vehicle electrical system will become overloaded and the rear lighting of the vehicle will cease to function. The TIPM will store a Diagnostic Trouble Code (DTC) for this condition.

TURN SIGNAL LAMPS

The turn signal lamps system includes the left (lighting) 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 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 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 SCM monitors a hard wired multiplex input from the left 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 the appropriate electronic turn signal request messages 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 control 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.

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.

WARNINGS

WARNING: To avoid serious or fatal injury, eye protection should be used when servicing any glass components.

CAUTION: Do not contaminate the glass of halogen bulbs with fingerprints or allow contact with other possibly oily surfaces. Reduced bulb life will result.

CAUTION: Do not use bulbs with higher candle power than indicated in the Bulb Application table. In addition, do not use fuses, circuit breakers or relays having greater amperage value than indicated on the fuse panel or in the Owner's Manual.

Damage to lamps, lenses, wiring and other related electrical components can result.