Code B119, Twilight Photocell Circuit: Notes

Fig 1: Code B119, Wiring Diagram (1 of 2) Twilight Photocell Circuit

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

Code B119 will set if ignition is on and signal voltage indicates more than 97 percent, open circuit voltage or less than 3 percent, which is shorted circuit voltage). During time failure is present, a substitute light reading (indicating darkness) will be used to allow continued operation of headlights. The measure of light reading, BD44 display, will indicate actual sensor reading.

1. Checks to see if open circuit is due to circuit or sensor. If open circuit reading changes to a shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.
2. By applying a 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.
3. Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.