BCM Code B121, Twilight Enable Switch: Notes

The twilight enable switch uses a physical control as the delay potentiometer. Inside left switch assembly, the enable switch contacts close when the time delay slider is moved to OFF position. The Instrument Panel Cluster (IPC) supplies voltage on circuit No. 304 to switch. When slider is moved from OFF position, the switch contacts close and signal voltage is pulled low through circuit No. 736 to ground.

Code B121 will set when ignition is on, twilight delay potentiometer is working properly (Code B120) and signal voltage is high when the delay slider is moved from OFF position (open circuit), or signal voltage is low when the delay slider is in OFF position (shorted circuit).

1. IPC input parameter II82 displays voltage state of circuit No. 304 at IPC. These conditions can be observed in IPC input display as readings of high or low when delay slider is moved.
2. Check to see if LO reading is caused by circuit or switch assembly. If display changes from LO to HI when the switch assembly is disconnected, IPC is okay.
3. Check to see if HI reading is caused by circuit or switch assembly. If display changes from HI to LO when switch terminals are jumped together, the IPC and wiring are okay.