Honda Multiplexing Board

Honda-Multiplexing Board Worksheet

This multiplex system was used for body controlled functions on 1996 to 2002 Honda accord and 1996 onward prelude. It utilises three nodes (control units) driver’s door, driver’s side and passenger side.

Multiplex Control System Circuit Diagram

(Input-Process-Output)



Node Control unit:

1 Driver’s Door

2 Driver’s Side

3 Passenger side

Communication Line:

1 Between driver unit and passenger unit: Pink (Driver - Pin #B1.Passenger – pin #B9)

2 From the door unit and the driver unit: Brown (Driver - Pin A2, Door pin - A15)

Supply Voltage:

Driver: Pin A1, A12 (white/black) and A24 (pink)

Passenger: Pin A22 (black) and A24 (Yellow)

Door: A1 (pink)

Earth:

Driver: Pin B11 and A14 (black)

Passenger: (Pin B22 and A8 (black)

Doors: Pin A12 and A19 (black)

Create a Fault

The passenger’s side window on the driver’s side is not working. The fault codes affect down switch to the window. DTC cannot identify this fault.

Analyse the fault

When we look at the fault our first step is to check the supply voltage (input) next we measure the voltage from one node to another. From there we have no communication from the passenger door as the window goes down. This is when we come to a conclusion that this cause between the nodes, the down mode relay is not communicate therefore the down switches of the relay is not respond

Mode 1 Test



After reading the manual put the system in to test mode 1. Note the codes (if any) and possible faults that the system gives you.

We haven’t identified or note any code at this point.

Go to step 5, can you conduct this test? Why /why not.

Mode 1 cannot give us the DTC and so the fault does not exist.

Communication test specification:

Test One: voltage between Door and driver

7.57volts

Test Two: voltage from Driver and Passenger

7.57volts

Both test match the spec and so the communication wire are in good condition.

Mode 2 Test

Mode 2 test is telling by the beep sound the window switch inputs is working perfectly. This explain to us the possible clue which the fault is coming from the passenger unit to the relay down switch and so we start diagnose by measure it.   

Explain your results and conclusions, Does it concur with your diagnosis from question

According to our result yes we have communication from our input but the output is not respond.

RELAY TEST

 Voltage supply: 87A and 87 12.00volts (This shows our input power to switching)

                 Input: 86 0.00v (No signal from the control circuit)

We check the relay switch supply voltage which is Pin #87, 87A (red) than we also check the voltage on earth. Pin #30 reading has 12volts (red). The passenger node recorded no voltage on 86 (red). this diagram show in/out-put terminal of the relay used to measure the voltage for our final test. 

The relay circuit shows no voltage to the control terminal (86), and it’s possible that is an open circuit. From here we can figure it out and what causes to our window as it switches down. The passenger node and the relay control are not powering up therefore the result of been damaging.