Operation

OPERATION

HEADLAMP POWER

The headlamp switch is a direct input to the Body Control Module (BCM). The BCM sends a Programmable Communication Interface (PCI) data bus message to the Integrated Power Module (IPM) informing it of a headlamp switch status change. The IPM then turns on power to the headlamps through four "fuseless" circuits. These circuits are electronically controlled and continuously monitored for malfunctions. Power is supplied to each filament in a separate circuit. On vehicles with HID lamps, the IPM provides power to the HID module which in turn, turns the lamps on. For vehicles equipped with Daytime Running Lamps (DRL), the IPM electronically steps down the headlamp voltage to provide the desired illumination. The DRL's will automatically extinguish when the blinker or hazards are activated and will come back on when the blinker or hazards are deactivated.

HEADLAMP SYSTEM

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 IPM 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 the PCI bus to the IPM informing the IPM 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.

OPTICAL HORN/HIGH BEAMS

When the multi-function switch is pulled to the first detent (optical horn) with the headlamps ON and the key-in the ignition, the BCM shall send a message via PCI bus to the IPM to turn on the headlamps drivers to illuminate all filaments (Low and High beams). When the multi-function switch is pulled to the second detent (high beam) and the headlamps are ON, the BCM shall send a message via PCI bus to the IPM to turn on the headlamps drivers. The High Beams and Low Beams are illuminated and the 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.

HEADLAMP SWITCH

The Headlamp Switch uses a multiplexed (MUX) circuit to the Body Control Module (BCM). The Headlamp Switch controls the Fog lamp relay, Park lamps and the Low and High beam headlamps. The BCM then sends a signal through the PCI data bus line to the IPM as to what state the switch has selected. The IPM energizes the high side output drivers to turn ON the desired lamps.

FRONT PARK and SIDE MARKER LAMPS

The park lamp switch is a direct input to the BCM. The BCM sends a PCI data bus message to the IPM informing it to turn on the park and side marker lamps. The park lamp relay is then powered through low side control of the IPM. This circuit is electronically controlled and continuously monitored for malfunctions. The IPM provides power through a high side driver.

HEADLAMP TIME DELAY SYSTEM

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).

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.

FRONT FOG LAMP

The fog lamp switch is a direct input to the BCM. The BCM sends a PCI data bus message to the IPM informing it to turn on the fog lamps. This circuit is electronically controlled and continuously monitored for malfunctions. Fog lamp functionality is not equipped on all vehicles. The IPM "learns" that the vehicle is equipped with fog lamps by reading the BCM data bus message. The Fog lamps can only be ON when the park and low beams are ON. If the high beams are switched ON then the Fog lamps will be automatically turned OFF.

EXTERIOR LIGHTING BATTERY SAVER

The BCM monitors the status of the control of the Park Lamps, Headlamps and Fog Lamps. If any exterior lamps are left ON after the ignition is turned OFF, the BCM will send this information to the IPM which will then turn the drivers OFF after 3 minutes.

AUTOMATIC HEADLAMPS

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 Computer (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 greater than 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

Power is reduced using pulse-width modulation (PWM) 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 IPM.