Code: P1🔧 Mitsubishi Mini Split

Mitsubishi Mini Split Error Code P1: Intake (Room Temperature) Sensor Error (Meaning, Causes, Fixes)

Reviewed 2026-10-24 · Based on 3 manufacturer & service sources

What the code means

Mitsubishi's Mr. Slim (P-series) service manuals list P1 as "Intake sensor error" in the indoor unit check-code table, and the troubleshooting table calls it an abnormality of the room temperature thermistor (TH1). The board checks this sensor all the time in cooling, drying and heating. A reading of 90 °C (194 °F) or more counts as a short, and -40 °C (-40 °F) or less counts as an open circuit. When either is detected the unit goes into 3-minute resume prevention mode, and P1 is set only if it doesn't return to normal after those 3 minutes. On the wireless remote self-check, P1 is 1 blink or beep. On some outdoor boards (for example the PUY-A NHA7/NKA7 series) the same fault shows as LED1 4 blinks and LED2 1 blink. P1 is the room air sensor; P2 and P9 are the indoor pipe sensors (TH2 liquid and TH5 condenser/evaporator).

Likely causes

Safe DIY checks

⚠ Before you start

The indoor controller board is reached with the unit's covers off and can carry line voltage. Switch off power at the breaker or disconnect before touching connectors or measuring thermistor resistance, and leave board work to a qualified HVAC technician.

  1. Turn the system off at the breaker or disconnect, wait a minute, then turn it back on. Mitsubishi's countermeasure ends with turning the power off and on again after the check, and a one-off glitch may clear.
  2. If P1 comes straight back, note the exact indoor model number from the unit's rating label. The sensor and board checks need the front panel and electrical cover off, which exposes live parts.
  3. Compare the room temperature shown on a wired remote controller (if you have one) with a thermometer next to the indoor unit. A reading that's way off, or stuck, points toward the sensor or board.
  4. Call a Mitsubishi dealer or HVAC technician for the connector, resistance and board checks below.

🛠 When to call a pro

  • With power off, check the TH1 resistance against Mitsubishi's table: about 15.0 kΩ at 0 °C (32 °F), 9.6 kΩ at 10 °C (50 °F), 6.3 kΩ at 20 °C (68 °F), 4.3 kΩ at 30 °C (86 °F) and 3.0 kΩ at 40 °C (104 °F). The thermistor is R0 = 15 kΩ ± 3%, about 5.4 kΩ at 25 °C (77 °F).
  • While measuring, gently pull and bend the lead wire. Mitsubishi notes this can reveal a broken wire or contact failure that a still reading misses.
  • Check the connector on the indoor controller board (CN20 for TH1 on the PLA-A BA4 manual; the Mr. Slim chart lists CN20, CN21, CN29 and CN44 for the indoor thermistors). Reseat it, turn the power on again and check whether the unit restarts.
  • Check the room temperature display on the remote controller. If it differs abnormally from the actual room temperature and the thermistor and wiring are good, replace the indoor controller board.
  • Turn the power off and on again to operate after the check.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Mini split room temperature thermistor (exact part for your indoor model)

A failed TH1 thermistor is Mitsubishi's first listed cause for P1; match the part number to your indoor unit's model.

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⚙

Indoor controller board

Replaced only after the thermistor and its connector check out. It must match your indoor unit's exact model.

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⚙

Digital multimeter

Used to check the thermistor's resistance against the service manual's table.

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Sources

  1. Mitsubishi Electric PLA-A BA4 service manual OCH482 (check-code table: P1 intake sensor error, 1 blink; troubleshooting: room temperature thermistor TH1 short 90 °C / open -40 °C, 3-minute resume prevention, causes, CN20, resistance table, R0 = 15 kΩ ± 3%)
  2. Mitsubishi Electric outdoor unit service manual OCH636E, PU(Y)(Z)-A12-42NKA7 (outdoor LED1 4 blinks / LED2 1 blink = abnormality of room temperature thermistor TH1, P1; check connectors CN20, CN21, CN29, CN44)
  3. Mitsubishi Electric Singapore, Mr. Slim error code chart (P1 intake sensor error, 1 blink; P1/P2/P9 checks)

Last reviewed 2026-10-24. Always confirm against the manual for your exact model number.