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CIRCUIT OPERATION

Headlight Operation
Battery voltage is applied at all times through Circuit Breaker 5 and CKT 661 to the coils and contacts of the Lo Beam and Hi Beam Relays. Both relays are controlled by the BCM at separate output terminals.

Lo Beam Operation
When the Headlight Switch is pressed terminal 1D9 (the headlight switch input) of the BCM is grounded through CKT 308. In response to this input the BCM energizes the Lo Beam Relay by grounding the relay coil at terminal 2A9 (the lo beam/redundant relay output) through CKT 911. When the Lo Beam Relay energizes voltage is applied through the relay contacts and CKT 12 to the lo beam filaments of both Headlamps.

Hi Beam Operation
Hi beam operation is enabled by pulling the Multi-Function (turn signal) Lever towards you. If the lo beams are already on the headlight system will change state to hi beams. If the lo beams are not on and the Ignition Switch is in RUN the hi beams will turn on for as long as the Multi-Function Lever is pulled and held inward (flash-to-pass).

When the Multi-Function Lever is pulled inward, the Headlight Dimmer Switch closes, grounding terminal 1D7 (the hi beam input) of the BCM through CKTs 307 and 803 at ground G302. The BCM then energizes the Hi Beam Relay by grounding the relay coil through CKT 912 at terminal 3C9 (the hi beam relay output). Voltage is applied to the hi beam filaments of both Headlamps through the relay contacts and CKT 11. The BCM also turns off the Lo Beam Relay whenever it turns on the Hi Beam Relay.

Twilight Sentinel
The BCM controls the Twilight Sentinel System. Twilight Sentinel automatically turns the headlights and park lights on and off by monitoring ambient light conditions. Twilight Sentinel also keeps the lights on for a delay period (0 to 180 seconds) when the ignition is turned off while the lights are on through Twilight Sentinel.

Twilight Enable
The BCM enables Twilight Sentinel when the Twilight Sentinel Switch is pressed and the Ignition Switch is in RUN. A twilight enable signal is sent through the lighting data line to the BCM from the Headlight Switch when the Twilight Sentinel Switch is pressed. When the Ignition Switch is turned to RUN battery voltage is applied to BCM terminal 3D6 (the ignition 3 input). The BCM turns on the lights during low ambient light levels through the lo beam/redundant relay output at terminal 2A9 and the park light relay output at terminal 3C10. These are the same output terminals the BCM uses to turn on the lights when manually selected from the Headlight Switch.

Twilight Photocell
The BCM monitors ambient light conditions through the Twilight Photocell at terminal 1D3 (the twilight photocell input). The Twilight Photocell is a variable resistor whose resistance changes as the level of ambient light changes around it. As ambient light decreases the resistance of the Twilight Photocell increases. The voltage level at the BCM twilight photocell input increases as the Twilight Photocell resistance increases.

If the Twilight Photocell, CKT 278 or CKT 736 opens, BCM Code B119 will set. A short to ground in CKT 278 or the Twilight Photocell will also set Code B119. An open in CKT 736 between the BCM and splice S228 will set multiple codes.

Twilight Delay
The setting of the Twilight Delay Switch in the Headlight Switch determines the twilight delay (lights timeout) after the ignition is turned off. The BCM monitors the Twilight Delay Switch at terminal 1C2 (the twilight delay input). As the Twilight Delay Switch is moved from - to + the voltage at BCM terminal 1C2 decreases. The BCM adjusts the twilight delay in 10-second intervals from 0 to 180 seconds in response to the voltage level at the twilight delay input.

The Twilight Delay Switch is a 20.2 K ohm slider potentiometer (variable resistor) with a 1.2 K ohm limiting resistor in series with the 5 volt supply from the BCM. In the - position, resistance is approximately 1.2 K ohms and most of the 5 volt supply from the BCM is dropped across the twilight delay input resistor in the BCM. As the Twilight Delay Switch is moved to the + position, the resistance of the switch increases and more of the 5 volt supply is dropped across the switch and less voltage is dropped across the twilight delay input resistor in the BCM.

If the Twilight Delay Switch opens or shorts to ground BCM Code B120 will set. If the 5 volt supply from the BCM or CKT 705 opens or shorts to ground multiple codes will set. An open in CKT 736 from splice S238 to the BCM also will cause multiple codes to set.

Daytime Running Lights (DRL)
On vehicles equipped with daytime running lights (option T61), the BCM turns on the lo beam Headlights and Park Lights whenever the Ignition Switch is in RUN and the transaxle is not in park. The daytime running lights feature will not activate if the Front Fog Lights, Park Lights or Headlights already have been turned on.

The BCM controls DRL based on the status of the following inputs:
^ (Ignition 3 input) The Ignition Switch must be in the RUN position. When the Ignition Switch is in RUN, battery voltage is applied through Fuse A13 and CKT 250 to terminal 3D6 of the BCM (the ignition 3 input).
^ (Park input) The park input must indicate that the transaxle is not in the park position. When the transaxle is in park, the Transaxle Range Switch is in the position shown on the schematic. When the Ignition Switch is in the RUN, BULB TEST or START position battery voltage is applied to terminal 3D8 (the park input) of the BCM through Fuse B9, CKT 439, the Transaxle Range Switch and CKT 275. Shifting the transaxle out of the park position opens the circuit at the Transaxle Range Switch and voltage is no longer applied to the park input of the BCM.
^ (Headlight status) The BCM will not activate DRL if the headlights already have been turned on through the Headlight Switch or Twilight Sentinel. Headlight Switch status is monitored at terminal 1D9 (the headlight switch input). The BCM monitors Twilight Sentinel status by checking the twilight photocell input and the Twilight Sentinel Switch state. The BCM monitors the Twilight Sentinel Switch state through the lighting data line.
^ (Park Light status) The BCM will not activate DRL if the Park Lights are on. Park Light Switch status is monitored through the lighting data line by the BCM.
^ (Front Fog Light status) The BCM also will not activate DRL if the Front Fog Lights are on. Front Fog Light Switch status is monitored through the lighting data line by the BCM.

The BCM activates the lo beam Headlights by energizing the DRL Headlight Relay. Battery voltage is applied to the coil of the relay through Fuse B11 and CKT 639 when the Ignition Switch is in RUN, BULB TEST or START. The BCM energizes the relay by grounding the coil through CKT 592 at terminal 2A11 (the DRL headlight relay output). When the relay energizes battery voltage is applied to the lo beam Headlamps through Circuit Breaker 5, CKT 661, the relay contacts and CKT 12.

The BCM activates the Park Lights by grounding the Park Light Relay coil at terminal 3C10 (the park light relay output). This is the same output the BCM uses to turn on the Park Lights for manual operation (from the Headlight Switch) and Twilight Sentinel operation.

When the lights are on through DRL the BCM will command the CCDIC message "HEADLAMPS SUGGESTED" (through the UART data line) when the Twilight Photocell indicates low ambient light.