Honda Multiplexing Board

The wiring diagram:

Communication Lines:
The communication line between door unit and driver unit is brown colour and pin #A15(door), #2(driver)
The communication line between driver unit and passenger unit is pink colour and pin #B1(driver), #9(passenger)

Earths and Voltage supply lines
Door Unit: Earth - A12 A19 Black,  Voltage supply - A1 pink
Driver Unit: Earth - A14 B11 Black,  Voltage supply - A1 white/black A12 pink A24
Passenger Unit: Earth - A8 B22 Black, Voltage supply - A22 yellow, A24

Create Fault:

The driver side rear window can goes up but can not goes down and relay does not switch, there is no click sound from the relay when switch down the window.

Analyze the fault
The connection between passenger unit to the relay may open circuit. The rely may not working. The door unit may not gives the signal to roll down the window.

Test mode 1:

The D.T.C of test mode 1:

The test mode 1 can not give us the D.T.C, that because this fault is not on the map of the test mode 1.

Check the open in the wire:
This is for communication test.
The specification:

Door unit to driver unit:

The voltage is 7.57V

Driver unit to passenger unit:

The voltage is 7.57V

The voltages are all in spec, so the wires of communication are good.

Test Mode 2:
Put the system to test mode 2 to test the inputs

Switch the input, if you can hear the sound, that means input are working fine.

The window switches inputs are all good.

For this fault, input and communication are all good, so the faults should be from the passenger unit to the window roll down relay.

Relay Check:
The voltage supply:

The voltage supply to the relay is 12.06V. It has the power to switching

the control circuit check.

There is no voltage to the control terminal of the relay, the control circuit is open circuit. That means the wire between the passenger unit and relay control terminal is broken.