Code B120, Twilight Delay Potentiometer: Notes

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

Code B120 will set if vehicle is equipped with twilight sentinel, ignition is on and signal voltage indicates less than 2 percent (open or grounded circuit) or greater than 98 percent (shorted to voltage). During time failure is present, a substitute delay time (minimum delay) will be implemented, allowing continued operation of twilight system. The reading from potentiometer BD43 display will indicate actual reading.

1. BD43 displays twilight delay time. The normal range is 2-98 percent.
2. Checks to see if open or grounded circuit reading is due to circuit or switch. If open or grounded circuit reading changes from a short to voltage reading after jumping switch assembly terminals, BCM and wiring are okay.
3. Measuring between circuit No. 705 (5 volts) and circuit No. 736 will determine if circuit No. 705 or 271 is open or shorted to ground.