Code B119, Twilight Photocell Circuit: Notes

The twilight sensor uses a photocell to control the signal voltage to the BCM. The BCM applies and monitors voltage on circuit No. 278 to the sensor. When the sensor detects darkness, its resistance is high, therefore, the BCM will see a high monitored voltage. As the sensor detects light, its resistance becomes less and the monitored voltage is pulled low through the ground, circuit No. 736. This signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B119 will set if the ignition is on and the signal voltage indicates more than 98 percent, open circuit voltage or less than 2 percent, which is shorted circuit voltage). During the time the failure is present, a substitute light reading (indicating darkness) will be used to allow continued operation of the headlights. The measure of light reading (BD44), however, will display the actual sensor reading.

1. BCM data value BD44 displays light level. The normal range is from 2-98 percent.
2. If the open circuit reading changes to a shorted circuit reading after jumping the sensor terminals, the BCM and wiring are okay.
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. Checks to see if the shorted circuit reading is due to the circuit or the sensor. If the shorted circuit reading changes to an open circuit reading after disconnecting the sensor, the BCM and wiring are okay.