Pioneer YN018GMFI16M2D Service Manual page 79

9.4.2.13 P5 (High temperature protection of condenser) error diagnosis and solution.
Error Code
Malfunction decision
conditions
Supposed causes
Trouble shooting:
P5
When outdoor pipe temperature is more than 65°C, the unit will
stop, and unit runs again when outdoor pipe temperature is less
than 52°C
● The condenser temperature sensor faulty
● Heat exchanger dirty
● System block