Code B123 - Courtesy Light Switch: Notes

The courtesy lamps panel switch is part of the dimmer control potentiometer. In the left switch assembly, the courtesy lamps enable switch closes when the dimmer is moved to the extreme right. The BCM supplies a signal voltage on circuit 685 which is pulled to ground through circuit 736 when the switch contact is closed.

Code B123 will set when the ignition is on, the dimming potentiometer has not failed (Code B122) and the signal voltage is high when the dimmer is moved to the enable position or the signal voltage is low when the dimmer is moved to the maximum dim position.

1. BCM input value BI01 displays the voltage state of circuit 685 at the BCM.
2. This step checks to see if the open circuit reading (HI) is due to the circuit or the switch assembly. If the display changes from HI to LO when the switch terminals are jumpered together, then the BCM and wiring are okay.
3. This step checks to see if the open circuit reading is due to the wiring or the BCM.
4. With courtesy lamps switch turned off, this step checks if the short to ground reading is due to the switch assembly or the wiring.