Mitsubishi Electric PUMY-P36NKMU3 Technical & Service Manual page 50

8-1-3. SELF-DIAGNOSIS ACTION BY FLOWCHART
Check code
0403
(Ed)
Abnormal points and detection methods
If serial communication between the outdoor controller board and outdoor
power board is defective.
●Diagnosis of defects
Make sure to turn the power OFF before connecting/disconnecting any connectors, or replacing boards.
Check the connection of the communication
line (CN2 and CN4) between the outdoor
controller board and power board.
Are they connected normally?
OCH733
Serial communication error
Diagnosis
No
Yes
Causes and checkpoints
1 Wire breakage or contact failure of connector CN2 or
CN4
2 Malfunction of power board communication circuit on
outdoor controller board
3 Malfunction of communication circuit on outdoor
power board
Connect the CN2 and CN4 properly.
Replace them in case of breakage.
The communication circuit of either the
outdoor controller board or power board is
defective.
If unable to identify the defective circuit;
Replace the outdoor controller board if it
does not recover.
Replace the outdoor power board.
50
Remedy