Pioneer YN018GMFI16M2D Service Manual page 72

9.4.2.9 P1 (High pressure protection) error diagnosis and solution. (Only for YN036GMFI16M4D)
Error Code
Malfunction decision
conditions
Supposed causes
Trouble shooting:
P1
If the sampling voltage is not 5V, the LED will display the
failure.
● Wiring mistake
● Over load protector faulty
● System block
● Outdoor PCB faulty