B119

BCM Code B119:

Twilight Photocell Circuit:

CIRCUIT DESCRIPTION:
The twilight sensor uses a photocell to control the signal voltage to the BCM. The BCM applies a voltage on CKT 278 to the sensor. When the sensor detects darkness its resistance is high, therefore the BCM will see a high signal voltage. As the sensor detects light its resistance becomes less and the signal voltage is pulled low through the ground, CKT 736. This signal voltage will vary between 5V (open circuit) and 0V (shorted circuit).

Code B119 will set if the ignition is "ON" and the signal voltage indicates more than 99% (open circuit) or less than 2% (shorted circuit). During the time the failure is present the twilight sentinel will not make a dark/light decision. The measure of light reading BD44 will display the actual sensor reading.

TEST DESCRIPTION: Test numbers refer to circled numbers on the diagnostic chart.

1. BCM data value BD44 displays light level. The normal range is from 2 to 99%.
2. Check to see if the open circuit reading is due to the circuit or the sensor. If the open circuit reading changes to a shorted circuit reading after jumpering the sensor terminals, the BCM and wiring are OK.
3. By applying a ground to various points in the circuits, an open can be isolated by observing whether the parameter display can be changed from the open reading to the shorted reading.
4. Check to see if the shorted circuit reading is due to the circuit on the sensor. If the shorted circuit reading changes to an open circuit reading after disconnecting the sensor, the BCM and wiring are OK.

NOTES ON INTERMITTENTS:
If an intermittent Code B119 is being set, manipulate the related wiring while observing BCM data value BD44. If the failure is induced, the reading will jump from its normal value to a reading outside the range of 2 to 99%.