Headlamps Suggested

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 bright to dark, the voltage at BCM pin "1D3" goes from 0 to 5 volts. If the BCM senses darkness via the twilight photocell, it has not turned the headlights "ON" because twilight sentinel is "OFF" and the headlight switch is "OFF," and all other failure conditions are met, the BCM will send the "HEADLAMPS SUGGESTED" 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 detected the need for headlamps yet. If the BCM has already detected the need for headlamps, it will use the second set of conditions. This is done so that once the message has appeared, it will remain even if the vehicle speed drops below 10 MPH.

TEST CONDITION(S):
1. Twilight photocell and circuits are OK
2. Ignition 3 is "ON."

FAILURE CONDITION(S):
1. Twilight photocell indicates darkness.
2. Headlamps are "OFF."
3. Vehicle speed greater than 10 MPH.
OR
1. "HEADLAMPS SUGGESTED" failure already present.
2. Twilight photocell indicates darkness.
3. Headlamps are "OFF."

ACTION TAKEN:
1. Display the "HEADLAMPS SUGGESTED" message on the CCDIC.