Code B123, Courtesy Lights Panel Switch Circuit: Notes

The panel lights switch uses the same physical control as the dimming pot. Inside the left switch assembly, the panel lamp switch contacts close when the dimming slider is moved to its extreme maximum position (on). The BCM supplies a voltage on circuit No. 685 to the switch. When the slider is moved to the extreme maximum position (on), the switch contacts close and the signal voltage is pulled low through ground circuit No. 804.

Code B123 will set if the ignition is on, the dimming pot has not failed (Code B122), and the signal voltage is low when the dimming slider is moved off of the maximum position (shorted circuit). A grounded circuit No. 685 will not only set Code B123, but will also turn the courtesy lights on at all times and run the battery down.

1. BCM input value BI01 displays the voltage state of the circuit at the BCM. These conditions can be observed in BCM input display BI01 as readings of "HIGH " or "LOW" when the dimming slider is moved. "HIGH" indicates circuit is not grounded and lights should be off.
2. Checks to see if the "LOW" reading is due to the circuit or the switch assembly. If the display changes from "LOW" to "HIGH" when the switch assembly is disconnected, the BCM and wiring are okay.
3. By removing the BCM connector, the short to ground can be isolated as being the wire or the BCM.