Code B120, Twilight Delay Potentiometer Circuit: Notes

The twilight sentinel uses a potentiometer to indicate desired time delay to BCM. The BCM supplies 5 volts on circuit No. 705 and ground on circuit No. 736 to resistor in left switch assembly. The delay wiper provides variable 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 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. Checks to see if open or grounded circuit reading is due to circuit or switch assembly. If open or grounded circuit reading changes to short to voltage reading after jumpering switch assembly terminals, BCM and wiring are okay.
2. Measuring voltage between circuit No. 705 and circuit No. 271 checks to see if circuit No. 271 is open or shorted to ground.
3. Checks to see if short to voltage circuit reading is due to the circuit or switch assembly. If short to voltage reading changes to an open circuit after disconnecting switch, BCM and wiring are okay.