B123

Code B123:

Twilight Photocell Circuit:

CIRCUIT DESCRIPTION:

The panel lamp 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 minimum "ON" position. The BCM supplies a voltage on CKT 685 to the switch. When the slider is moved to the extreme minimum dimming "ON" position, the switch contacts close and the signal voltage is pulled "LO" through ground CKT 804.

Code B123 will set, if the dimming pot has not failed (Code B122), and the signal voltage is "LO," when the dimming slider is moved off of the minimum position (shorted circuit) or signal voltage is "HI," when the dimming slider is moved to the "ON" position, minimum dimming (open circuit). During the time the failure is present the opposite state of the switch signal ("ON" vs. "OFF") will be implemented to allow continued operation or courtesy lamps.

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

1. BCM input valve BI01 displays the voltage state of the circuit, at the BCM. These conditions can be observed in BCM input display BI01 as readings or "HI" or "LO," when the dimming slider is moved.

2. Checks 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, the BCM and wiring are OK.

3. Checks to see if the "HI" reading is due to an open in CKT 686 or CKT 804. If the display changes from "HI" to "LO" when a known good GRD is provided, CKT 804 is open.

4. Checks to see if the "HI" reading is due to the circuit, or the BCM. If the display changes from "HI" to "LO," when the BCM terminal cavity is jumpered to ground, the BCM is OK.

5. Checks to see if the "LO" reading is due to the circuit, or switch assembly. If the display changes from "LO" to "HI," when the switch assembly is disconnected, the BCM and wiring are OK.

NOTE ON INTERMITTENTS:

If an intermittent code B123 is being set, manipulate the related wiring. When BCM input BI01 change of state indicator displays an "X," check the circuit for an intermittent open or short.