"Headlamps Are On" Message

FAILURE CONDITION(S)
1) ignition 3 voltage present.
2) Headlamps are on.
3) Twilight photocell detects daylight.
OR
1) ignition 3 voltage not present (ignition off).
2) Headlamps are on.

ACTION TAKEN
1) Display the "Headlamps Are On" message on the Computer Control Driver Information Center (CCDIC).

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 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 3D5 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 Driver Information Center (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.

DIAGNOSIS
Refer to Lighting and Horns for headlamp diagnosis. Lighting and Horns