Code B119 - Twilight Photocell Circuit: Notes

The twilight sensor uses a photocell to control signal voltage to BCM. The BCM supplies voltage on circuit No. 278 to sensor. When sensor detects darkness, resistance is high, therefore BCM will see high signal voltage. As sensor detects light, resistance is lowered, signal voltage is pulled low through circuit No. 736 to ground. Signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B119 will set when ignition is on, signal voltage indicates more than 94 percent (open circuit) or less than 6 percent (shorted circuit). During a failure, a substitute light reading (indicating darkness) will be used to allow continued operation of headlights and light reading BD44 will display actual sensor reading.

1. BCM data code BD44 displays light level. Normal range is 6-94 percent.
2. Checks if open circuit is caused by circuit or sensor. If open circuit reading changes to shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.
3. By applying ground to various points in circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.
4. Checks if short circuit reading is caused by circuit or sensor. If short circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.