B121

BCM Code B121:

Twilight Delay Switch Pot Circuit:

DESCRIPTION:

The twilight enable switch uses the same physical control as the delay pot. Inside the left switch assembly the enable switch contacts close as soon as the time delay slider is moved off of its extreme minimum (OFF) position. The IPC supplies a voltage on CKT 304 to the switch. When the slider is moved from the off position the switch contacts close and the signal voltage is pulled low through ground CKT 736.

Code B121 will set if the ignition is on, the twilight delay pot has not failed (code B120) and signal voltage is high when the delay slider is moved from the off position (open CKT), or signal voltage is low when the delay slider is in the off position (shorted CKT).


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. IPC input value II82 displays the voltage state of CKT 304 at the IPC. These conditions can be observed in IPC input display as readings of high or low when delay is moved.

2. Check to see if the LO reading is due to the circuit or the switch assembly. If the display changes from "LO" to "HI" when the switch assembly is disconnected, then the IPC is OK.

3. Check to see if the Hi reading 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 IPC and wiring are OK.

NOTE ON INTERMITTENTS:

When IPC II82 input change-of-state indicator displays an "X" check the circuit for an intermittent open.

Cycle twilight control between off and max delay. If BCM data BD43 does not read 6 to 94, then replace left switch assembly.