What it means
Mitsubishi calls it the intake sensor (thermistor TH1). It counts as faulty at 90°C or more (short) or -40°C or less (open), and the unit goes into a 3-minute pause first. With a wireless remote, the self-check reports it as 1 beep and 1 flash. On MSZ wall units, a room or coil sensor fault shows as 2 blinks of the OPERATION INDICATOR lamp followed by a 2.5-second gap (MSZ-FH and MSZ-AP service manuals).
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 P1 comes straight back, leave the unit 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 on the indoor control board, a broken sensor wire, 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 P1 error code mean?
The sensor that measures the air coming into the indoor unit is reading as short-circuited or disconnected. Mitsubishi calls it the intake sensor (thermistor TH1). It counts as faulty at 90°C or more (short) or -40°C or less (open), and the unit goes into a 3-minute pause first. With a wireless remote, the self-check reports it as 1 beep and 1 flash. On MSZ wall units, a room or coil sensor fault shows as 2 blinks of the OPERATION INDICATOR lamp followed by a 2.5-second gap (MSZ-FH and MSZ-AP service manuals).
Can I fix Mitsubishi P1 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 on the indoor control board, a broken sensor wire, or a faulty indoor control board.
Is Mitsubishi P1 worth repairing?
Worth fixing. The sensor, its wire or its plug is the first thing checked. Mitsubishi only points to the control board if the sensor tests fine.
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)
- Mitsubishi Electric MSZ-AP15/20VG indoor unit Service Manual OBH838 (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.