Lighting and Horns: Description and Operation

LAMPS/LIGHTING - EXTERIOR

LAMP SYSTEMS
Lighting circuits are protected by fuses. Lighting circuits require an overload protected power and high side drivers source, ON/OFF device, lamps and body grounds to operate properly. Plastic lamps require a wire in the harness to supply body ground to the lamp socket. Replace sockets and bulbs that are corroded.

Some of the interior and exterior lighting functions are governed by the Body Control Module (BCM). The headlamp, dome, and the door ajar switches provide signals to the BCM. The BCM in turn sends a Programmable Communication Interface (PCI) bus message to the Front Control Module (FCM) to enable the necessary drivers to set the required illumination configuration.

Wire connectors can make intermittent contact or become corroded. Before
coupling wire connectors, inspect the terminals inside the connector. Male terminals should not be bent or disengaged from the insulator. Female terminals should not be sprung open or disengaged from the insulator. Bent and sprung terminals can be repaired using needle nose pliers and pick tool. Corroded terminals appear chalky or green. Corroded terminals should be replaced to avoid recurrence of the problem symptoms.

Begin electrical system failure diagnosis by testing related fuses in the fuse block and intelligent power module. Verify that bulbs are in good condition and test continuity of the circuit ground. Refer to the appropriate wiring information.

AUTOMATIC HEADLAMP SYSTEM
The Automatic Headlamp system turns the instrumentation and exterior
illumination lamps ON when the ambient light levels are Night and the engine RPM is 450 or above, and OFF when light levels are Day.

Automatic headlamps are controlled by the Body Control Module (BCM). With the headlamp switch in the AUTO position, the BCM will control the headlamp, parking, side marker, tail and instrumentation lamps based on ambient light levels. Ambient light levels are monitored by the BCM using the Day/ Night signal and Electrochromatic Mirror (ECM) present from the Compass Mini Trip (CMTC) located on the front windshield in front of the rear view mirror ECM. Ambient light readings are averaged to limit cycling the lamps ON and OFF when passing through areas with varying light levels. The automatic headlamps will only function when the engine is running with RPM > 450. When the headlamp switch is in the AUTO position (Automatic mode), the Headlamp Time Delay system will function when the ignition switch is placed in any position other than run/start.

DAYTIME RUNNING LAMPS
Operating the high-beam headlamps at reduced power provides daytime running lamps, which are required on all new Canadian vehicles. Daytime running lamps are functional when 450 rpm's are reached.

Power is reduced using pulse-width modulation to the high beams, where by the power is switched on and off rapidly instead of remaining on continuously. The duration and interval of the power pulses is programmed into the FCM. Daytime running lamps are functional when 450 rpm's are reached.

HEADLAMPS ON WITH WINDSHIELD WIPERS
For vehicles equipped with the Automatic Headlamp System, the instrumentation and exterior illumination lamps will be turned ON when the headlamp switch is in the AUTO position, RPM > 450 and the windshield wipers have been in the intermittent, low or high mode of operation for more than ten seconds. When the windshield wipers are turned OFF the Body Control Module will determine if the instrumentation and exterior illumination lamps should remain ON base upon the current ambient light level.

HEADLAMP SYSTEM
The configuration of the headlamp system of headlamps, park lamps and fog lamps is determined by the BCM. The BCM determines the lighting configuration as a result of the inputs from the ignition switch, headlamp switch and multi-function switch. A PCI bus is transmitted from the BCM to the FCM to enable the necessary drivers to set the illumination configuration. Four wires are connected between the headlamp switch and the BCM. The first wire contains information regarding the position of the headlamp switch (Off, Automatic Headlamps, Automatic Headlamp switch fog, Park with Fog, Head, or Head with Fog Lamps). The second wire contains information regarding the position of the dimmer switch (Dome Lamp, Daytime Brightness, Dimming Level or Off). The third wire is a dedicated signal return (ground) wire. The fourth wire provides power to the front fog lamp indicator.

The headlamp system will default to headlamps ON position when ignition switch is ON and when an open or short circuit failure occurs on the headlamp switch input or PCI data bus communication between the BCM and the FCM fails. The system will return to normal operation when the open or short is repaired. A fault will be reported by the BCM when a failure occurs on the dimmer or headlamp switch input.

If the exterior lamps are ON and the headlamp switch is in any position other than OFF or AUTO and with the ignition switch OFF (LOCK) after 3 minutes the BCM sends a message via PCI bus to the FCM informing the FCM to turn off the headlamps, park lamps and fog lamps. This feature prevents the vehicle battery from being discharged when the vehicle lights have been left ON.

HEADLAMP TIME DELAY SYSTEM
The headlamp time delay system is controlled by the Body Control Module (BCM) via a PCI bus message transmitted by the BCM to the FCM to turn off the headlamps.

The headlamp time delay system is activated by turning the headlamps ON (high or low beam) while the engine is running, turning the ignition switch OFF, and then turning the headlamp switch OFF within 45 seconds. The system will not activate if more than 45 seconds elapse between ignition switch OFF and headlamp switch OFF. The BCM will allow the headlamps to remain ON for 90 seconds (configurable) before they automatically turn off (If the key is in the ignition during the headlamp time delay mode, then both the headlamps and park lamps (including panel dimming) will be ON). Refer to the Owner's Manual for more information.

If the headlamp switch is in the Auto Headlamp Position, the headlamps are ON due to the night signal from the CMTC and the ignition switch is in any position other than run/start, the BCM shall enter a 90 second (configurable) Auto Headlamps time delay mode. If the key is in the ignition during the headlamp time delay mode, then both the headlamps and park lamps (including panel dimming) will be ON. If the key is not in the ignition, then only the headlamps will be ON. The BCM will allow the headlamps to remain ON for 90 seconds before they automatically turn OFF.

OPTICAL HORN/HIGH BEAMS
When the multi-function switch is pulled to the first detent (optical horn) signal, the headlamps are ON, key-in the ignition the BCM shall send a message via PCI bus to the FCM to turn on the headlamps drivers to illuminate all four filaments (Low and High beams). When the multi-function switch is pulled to the second detent (high beam) signal and the headlamps are ON, the BCM shall send a message via PCI bus to the FCM to turn on the headlamps drivers. The High Beams are illuminated and the Low Beams and Fog Lamps (if ON) are extinguished. If the headlamps were in the high beam configuration when power was removed from the headlamps, the headlamps will be configured as low beam the next time they are activated.

NOTE: For RG - Export vehicles, the low beams and front fog lamps will remain ON when high beams are activated.