Headlamps Are on

Headlamp 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 left switch pod communicates this to the BCM on the lighting dataline. The BCM then turns the appropriate lights on or off. The BCM also monitors the twilight photocell input. The twilight photocell acts like a variable reistor. 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 bright to dark, the voltage at BCM pin 3D5 gores 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 "Headamps 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:

None.

FAILURE CONDITION:

1. Twilight photocell detects daylight.
2. Headlamps are on.
3. Ignition 3 voltage present.
4. Ignition 3 voltage not present (ignition off).
5. Headlamps are on.

ACTION TAKEN:

Display the "Headlamps Are On" message on the CCDIC.