Code: P9🔧 Mitsubishi Mini Split

Mitsubishi Mini Split Error Code P9: Pipe (TH5) Sensor Error (Meaning, Causes, Fixes)

Reviewed 2026-10-24 · Based on 4 manufacturer & service sources

What the code means

Mitsubishi's Mr. Slim (P-series) service manuals list P9 as "Pipe (TH5) sensor error" in the indoor unit check-code table, and the troubleshooting table calls it an abnormality of the pipe temperature thermistor, condenser-evaporator (TH5). The board checks this sensor all the time in cooling, drying and heating, except during defrost. 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 protection mode, and P9 is set only if it doesn't return to normal within those 3 minutes. On the IR wireless remote self-check, P9 is 2 blinks or beeps, the same count as P2. On some outdoor boards (for example the PUY-A NHA7/NKA7 series) it shows as LED1 4 blinks and LED2 1 blink, shared with P1 and P2. P9 is the condenser/evaporator pipe sensor; P2 is the liquid pipe sensor (TH2), P1 is the room air sensor (TH1), and P8 is a pipe temperature error where the sensors read fine but the coil isn't changing temperature as expected.

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. Refrigerant circuit work needs an EPA-certified 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, and a one-off glitch may clear.
  2. If P9 comes straight back, note the exact indoor model number from the unit's rating label. The thermistor sits in a holder on the indoor coil piping and its connector is on the indoor controller board, so the checks need covers off and expose live parts.
  3. Clean or replace the air filter if it's dirty. It won't fix a broken sensor, but it rules out an airflow problem making the coil run unusually cold or hot.
  4. Call a Mitsubishi dealer or HVAC technician for the connector, resistance, refrigerant and board checks below.

🛠 When to call a pro

  • With power off, check the TH5 resistance against Mitsubishi's table (TH1, TH2 and TH5 share it): about 15 kΩ at 0 °C (32 °F), 9.6 kΩ at 10 °C (50 °F), 6.3 kΩ at 20 °C (68 °F), 5.4 kΩ at 25 °C (77 °F), 4.3 kΩ at 30 °C (86 °F) and 3.0 kΩ at 40 °C (104 °F). R0 = 15 kΩ ± 3%, B = 3480 ± 2%.
  • Check for contact failure at CN44 on the indoor controller board. Reseat it, turn the power on and check whether the unit restarts.
  • Operate in test run mode and read the condenser/evaporator pipe temperature on the outdoor controller board (Mitsubishi says to connect the A-Control Service Tool PAC-SK52ST for this). If it's extremely low in cooling or extremely high in heating, the refrigerant circuit may have a defect.
  • If the displayed pipe temperature is very different from the actual pipe temperature and the thermistor and wiring check out, replace the indoor controller board.
  • If none of the above is found, Mitsubishi says there is no abnormality in the unit; turn the power off and on again to operate.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Mini split condenser/evaporator pipe thermistor (exact part for your indoor model)

On some models TH2 and TH5 come as one assembly on the CN44 connector; match the part number to your indoor unit's model.

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⚙

Indoor controller board

Replaced only after the thermistor, connector and refrigerant circuit 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: P9 pipe (TH5) sensor error, 2 blinks; troubleshooting: TH5 short 90 °C / open -40 °C, 3-minute resume protection, causes, CN44, test-run pipe temperature check with PAC-SK52ST; thermistor table R0 = 15 kΩ ± 3%, B = 3480)
  2. Mitsubishi Electric PKA-A12HA7/PKA-A18HA7 indoor unit service manual OCH637 (self-diagnosis table: P9 pipe (TH5) sensor error, 2 blinks/beeps)
  3. Mitsubishi Electric outdoor unit service manual OCH636E, PU(Y)(Z)-A12-42NKA7 (outdoor LED1 4 blinks / LED2 1 blink = abnormality of pipe temperature thermistor condenser-evaporator TH5, P9; check connectors CN20, CN21, CN29, CN44)
  4. Mitsubishi Electric Singapore, Mr. Slim error code chart (P9 pipe (TH5) sensor error; P1/P2/P9 checks)

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