BCM DTC B119: Twilight Photocell Circuit: Description

The twilight sensor uses a photocell to control the signal voltage to the BCM. The BCM applies a voltage on CKT 278 to the sensor. When the sensor detects darkness its resistance is high, therefore the BCM will see a high signal voltage. As the sensor detects light its resistance becomes less and the signal voltage is pulled low through the ground circuit 736. This signal voltage will vary between 5V (open CKT) and 0V (shorted CKT).