DTC B120: Twilight Delay Switch Pot Circuit: Description

The twilight delay uses a potentiometer to control the signal voltage to the BCM. The BCM, supplies voltage on circuit No. 705 to the resistor in the left switch assembly and returns as a ground to the BCM on circuit No. 736. The wiper provides the voltage signal to the BCM on circuit No. 271 indicating position of the slider and delay time. When the slider is moved toward the maximum position (maximum delay), resistance is low, therefore the BCM will see a high signal voltage. As the slider is moved toward the minimum position (minimum delay), its resistance increases and the signal voltage decreases. This signal voltage will vary between zero (0) volts (open or grounded circuit) and 5 volts (shorted to voltage circuit). BD43 displays a low percentage for minimum delay and a high percentage for maximum delay of headlight "ON" time.

Code B120 will set if the ignition is on and the signal voltage indicates less than 6% (open or grounded circuit) or over 94% (shorted to voltage). During the time the failure is present, a substitute delay time (minimum delay) will be implemented to allow continued operation of the twilight system. The reading from the potentiometer BD43, however, will display the actual reading.