Headlamps Are ON

Headlight Switch Circuit:

CIRCUIT DESCRIPTION:
The BCM controls the distributed lighting system via the lighting dataline. If the twilight "ON/OFF" switch, the headlight switch or the parklamp switch is pressed, the headlight switch communicates this to the BCM on the lighting dataline. The BCM then drives the appropriate relay to turn the lights "ON" or "OFF." The BCM also monitors the twilight photocell input. The twilight photocell acts like a variable resistor. When it detects bright light it has a very low resistance, and when it detects darkness, it has a very high resistance. As the light detected by the photocell goes from dark to bright, the voltage at BCM pin "1D3" goes from 5 to 0 volts. If the BCM senses daylight via the twilight photocell, it has turned the headlamps "ON" because the headlamp switch was pushed, and all other failure conditions are met, the BCM will send the "HEADLAMPS ARE ON" message to the DIC.

The failure conditions are divided up into two sets. The first set of conditions is used if the BCM has not already sent this message to the DIC. If the BCM has already sent this message to the DIC, it will use the second set of conditions. This is done so that once the message has appeared, it will remain even if the twilight photocell indicates darkness.

TEST CONDITION(S):
None

FAILURE CONDITION(S):
1. Ignition 3 voltage present.
2. Headlamp switch is "ON."
3. Twilight photocell detects daylight.
4. Twilight photocell previously indicated dark with park lamps "ON."
OR
1. Ignition 3 voltage not present (Ignition "OFF").
2. Headlight switch is "ON."

ACTION TAKEN:
1. Display the "HEADLIGHTS ARE ON" message on the CCDIC.