BCM Code B122, Panel Light Dimming Pot Circuit: Notes

The panel dimmer uses a potentiometer to control signal voltage to BCM. The BCM supplies voltage on circuit No. 705 to resistor in left switch assembly and returns to BCM on circuit No. 736 as ground. Wiper provides voltage signal to BCM on circuit No. 686 indicating position of thumbwheel and dim level. When thumbwheel is moved toward maximum (bright), resistance is low; therefore, BCM will see a high signal voltage. When thumbwheel is moved toward minimum (dim), resistance is higher and signal voltage to BCM becomes less.

Code B122 will set when ignition is on and signal voltage indicates less than 6 percent (open or grounded circuit) or more than 94 percent (shorted to voltage). During a failure, a substitute dimming value will be used to allow continued operation of interior lighting and potentiometer reading BD42 will display actual sensor reading.

1. BCM parameter BD42 displays amount of panel dimming. Normal range is 6-94 percent.
2. Check to see if open circuit is caused by circuit or switch assembly. If open or grounded circuit reading changes to shorted to voltage reading after jumping switch terminals, BCM and wiring are okay.
3. Measuring voltage between circuit No. 705 (5 volts) and circuit No. 686 will determine if circuit No. 686 is open or shorted to ground.
4. Check to see if short to voltage reading is caused by circuit or switch assembly. If short to voltage reading changes to an open circuit reading after disconnecting switch assembly, BCM and wiring are okay.