What it means
Mitsubishi's thermistor TH5. It counts as faulty at 90°C or more (short) or -40°C or less (open), and it is not checked during defrost. With a wireless remote, the self-check reports it as 2 beeps and 2 flashes, the same as P2. On MSZ wall units, a coil sensor fault shows as 2 blinks of the OPERATION INDICATOR lamp followed by a 2.5-second gap.
What to check, in order
- Write down the code
Note the code and unit number, as Mitsubishi's operation manual asks.
- Switch off and on once
Turn the system off at the breaker or isolator and back on. If P9 returns, leave it off and book a repair.
When to call an engineer
Call an air conditioning engineer (UK) or HVAC technician (US). Mitsubishi lists a faulty sensor, a poor contact at its connector, a broken sensor wire, a refrigerant circuit fault, or a faulty indoor control board.
A repair visit will usually check the sensor's reading and its wiring.
- Note the model and serial number. They're on a label on the side of the indoor unit, and on the outdoor unit.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Quick answers
What does the Mitsubishi P9 error code mean?
The sensor on the indoor coil (the condenser/evaporator pipe) is reading as short-circuited or disconnected. Mitsubishi's thermistor TH5. It counts as faulty at 90°C or more (short) or -40°C or less (open), and it is not checked during defrost. With a wireless remote, the self-check reports it as 2 beeps and 2 flashes, the same as P2. On MSZ wall units, a coil sensor fault shows as 2 blinks of the OPERATION INDICATOR lamp followed by a 2.5-second gap.
Can I fix Mitsubishi P9 myself?
Engineer only (engineer visit). Start with: write down the code; switch off and on once. Call an air conditioning engineer (UK) or HVAC technician (US). Mitsubishi lists a faulty sensor, a poor contact at its connector, a broken sensor wire, a refrigerant circuit fault, or a faulty indoor control board.
Is Mitsubishi P9 worth repairing?
Worth fixing. A sensor or connection fault is the first thing checked. Worth repairing.
Checked against
- Mitsubishi Electric SLZ-KF09/12/15/18NA1 ceiling cassette (M-series) Technical & Service Manual TCH118A (PDF)
- Mitsubishi Electric SLZ-M15-60FA ceiling cassette Technical & Service Manual OCH522 (PDF)
- Mitsubishi Electric SEZ-KD09/12/15/18NA(4) ducted (M-series) Technical & Service Manual HWE0802B (PDF)
- Mitsubishi Electric PCA-M35-140KA indoor unit Service Manual OCH659 (PDF)
- Mitsubishi Electric MSZ-FH06-18NA(2) indoor unit Service Manual OBH683E (PDF)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.