Code B120, Twilight Delay Switch Pot Circuit: Notes

The twilight delay uses a potentiometer to control the signal voltage to the BCM. The BCM supplies and monitors 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, the BCM will see a high monitored voltage on circuit No. 271. As the slider is moved toward the minimum position (minimum delay), resistance increases and the monitored voltage decreases. This signal voltage will vary between zero 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 2 percent (open or grounded circuit) or greater than 98 percent (shorted to voltage). During the time the failure is present, a substitute delay time (minimum delay) will be used to allow continued operation of the twilight system. The reading from the potentiometer BD43, however, will display the actual reading.

1. BCM data value BD43 displays twilight delay time. The normal range is 2-98 percent.
2. Checks to see if the open or grounded circuit reading is due to the circuit or the switch. If the open or grounded circuit reading changes from a short to voltage reading after jumping the switch assembly terminals, the BCM and wiring are okay.
3. Measuring between circuit No. 705 (5 volts) and circuit No. 271 will determine if circuit No. 271 is open or shorted to ground.
4. Checks to see if the short to voltage circuit reading is due to the circuit or the switch assembly. If a short to voltage reading changes to an open circuit reading after disconnecting the switch assembly, the BCM and wiring are okay.