B120 Twilight Delay Pot Circuit

Chart:

Schematic:

DESCRIPTION
The twilight delay uses a potentiometer to control the signal voltage to the Body Control Module (BCM). The BCM supplies voltage on CKT 705 to the resistor in the left switch assembly and returns as a ground to the 13CM on CKT 736. The wiper provides the voltage signal to the BCM on CKT 271 indicating position of the slider and delay time.

When the slider is moved toward the max. position, resistance is low, therefore, the BCM will see a high signal voltage. As the slider is moved toward the min. position its resistance increases and the signal voltage decreases. This signal voltage will vary between O Volts (open or grounded CKT.) and 5 Volts (shorted to voltage).


Code B120 will set if the ignition is on and the signal voltage indicates less than 6% (open or grounded CKT) 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.

TEST DESCRIPTION
The numbers below refer to circled numbers on the diagnostic chart:
1. BCM data value BD43 displays twilight delay time. The normal range is 6 to 94%.
2. Check to see if the open or grounded circuit reading is due to the circuit or the switch assembly. If the open or grounded circuit reading changes to a short to voltage reading after jumpering the switch assembly terminals, the BCM and wiring are OK.
3. Measuring the voltage between CKT 705 (5 volts) and 271 will determine if CKT 271 is open or shorted to ground.
4. Check 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 OK.

NOTES ON INTERMITTENTS
If an intermittent Code 13120 is being set, manipulate the related wiring while observing BCM data value BD43. If the failure is induced, the reading will jump from its normal value to a reading outside the range of 6 to 94%.