Mitsubishi Electric Coil Sensor Code
Mitsubishi P2 Error Code
If your controller shows the Mitsubishi P2 error code, the indoor unit has lost a trustworthy reading from the sensor on its coil liquid pipe. This is a Mitsubishi Electric code. Below we explain what it means, how it differs from similar codes, and what a technician does to fix it.
In Plain Words
What Is the P2 Code Telling Me?
Every Mitsubishi Electric indoor unit carries more than one temperature sensor. One reads the room air. Others are clipped to the copper pipework of the indoor coil. P2 points to the sensor on the liquid pipe, which most service manuals label TH2.
When that sensor reads open circuit or short circuit, the indoor board flags P2 and stops the system. The board needs this reading to manage the coil safely, so it will not carry on without it.
Put simply, P2 is a coil sensor fault. It is not, in itself, a refrigerant leak, a dead compressor or a wiring fault between the indoor and outdoor units. That distinction matters, because it narrows the repair to a small group of parts.
Maker
Mitsubishi Electric. Mitsubishi Heavy Industries uses numbered E codes, and its indoor coil sensor fault has a different code entirely.
Part
The liquid pipe thermistor, usually TH2, mounted on the indoor coil pipework and wired back to the indoor controller board.
Effect
The indoor unit stops, because it cannot monitor the coil for freezing in cooling or overheating in heating.
Why It Matters
Why Does the Indoor Unit Need a Liquid Pipe Reading?
The coil is where the real work happens. In cooling, cold refrigerant flows through it and pulls heat out of the room air. In heating, the flow reverses and hot refrigerant warms the air instead. Either way, the coil temperature has to stay within safe limits.
The liquid pipe sensor helps the board watch those limits. It feeds into decisions about fan speed, compressor speed, frost prevention and when to warm the fan up in winter. Without it, the board cannot protect the coil from icing up or running too hot.
As a result, Mitsubishi Electric chose a cautious approach. If the reading is clearly wrong, the unit stops and asks for attention. That protects the coil and the compressor from damage that would cost far more to fix.
Spotting It
How Do I Read a P2 Code on My System?
On a wired wall controller, P2 normally appears on screen. Write down the code and any unit number beside it. Ducted and cassette owners usually see it this way.
With a wireless remote, you may need the self check function. In general terms, entering check mode and pointing the remote at the indoor unit makes the unit reply with beeps and lamp flashes. Many ducted and cassette manuals list two beeps and two flashes for this fault.
Here is a useful quirk. On some ranges, P2 and P9 share the same two flash pattern. P9 relates to a different coil sensor, so the lamp alone cannot tell you which one has failed. A wired controller or the technician’s service tools will separate them. For wall splits with only an operation lamp, two blinks then a pause is the typical indoor coil sensor pattern on ranges like the MSZ-AP.
Root Causes
What Usually Causes a Mitsubishi P2 Fault?
The coil is a harsher place for a sensor than the room air intake. It gets cold and wet in summer and hot in winter. Over time, that cycling takes a toll. Here are the common causes, starting with the simplest.
Connection Problems
- The sensor plug on the indoor board has lost firm contact.
- Condensation has crept along the lead and corroded the pins.
- The clip or holder has slipped, leaving the sensor loose on the pipe.
- A recent service disturbed the lead while panels were off.
Component Problems
- The thermistor bead has cracked after years of hot and cold cycles.
- The lead has broken internally where it bends near the coil.
- Pests have damaged the cable inside a ceiling or bulkhead.
- The indoor controller board input has failed, normally confirmed last.
Because the coil gets wet during cooling, moisture related faults are more common here than with the room sensor. Owners often notice P2 appearing on a humid day, then disappearing once the weather dries out. That pattern strongly suggests a connection issue.
Your Part
Which Checks Are Safe for a Homeowner?
A coil sensor sits behind panels and near live parts. Therefore, owner checks are limited to the outside of the unit. Even so, they can save time on the day.
- Note whether P2 appeared in cooling, heating or dry mode, and the weather at the time.
- Try one full power reset at the circuit breaker, waiting a few minutes before switching back on.
- Check that the filters are clean, since a clogged filter can make the coil run colder and wetter.
- Look for water marks or drips around the indoor unit, but do not open it.
- If you have a multi head system, note which head shows the code.
- Take a photo of the model label on the side of the indoor unit.
Please stop there. Do not remove the front cover to look for the sensor, pull on wires or spray anything onto the coil. Those steps can create new faults or expose you to mains voltage.
The Repair
How Will a Technician Diagnose and Fix P2?
A licensed technician follows a logical path from the sensor back to the board. Each step either confirms or rules out a part.
Review the History
They check the stored codes on the controller or board. Repeated P2 entries, or P2 with P9, can point towards a shared connector.Isolate and Inspect
With power off, they remove the panels, locate the liquid pipe sensor and confirm it is firmly seated in its holder on the pipe.Measure the Thermistor
They unplug the sensor and measure its resistance. That figure is compared with the resistance chart for the actual pipe temperature.Check the Lead and Plug
The lead is traced for damage, and the board connector is checked for corrosion or loose pins.Replace and Confirm
A faulty sensor is swapped for the correct part. The system is then run and the reading compared with the real coil temperature.
If every sensor test passes yet P2 remains, the indoor board becomes the suspect. The technician will talk through that outcome before ordering a board, since it is a larger job.
System Types
Does P2 Behave Differently on Ducted, Cassette and Wall Units?
The meaning stays the same across Mitsubishi Electric indoor units. What changes is how you see the code and how hard the sensor is to reach. That affects how long the repair takes and how you should prepare for the visit.
Wall Splits
On MSZ wall units, the coil sensor sits behind the front cover. Access is usually straightforward from a ladder. Since many wall units lack a screen, the fault shows as a lamp pattern rather than letters.
Ceiling Cassettes
Cassettes hide their coil above the ceiling grille. The technician removes the decorative panel and sometimes the drain pan cover. A wired controller usually displays P2 clearly, which speeds up diagnosis.
Ducted Units
Ducted indoor units normally live in the roof or under the floor. The sensor is inside the cabinet, so access through a hatch is essential. Expect a little more time for these jobs.
Multi head systems add one more wrinkle. Several indoor units connect to a single outdoor unit, and each indoor unit has its own coil sensors. A P2 on one head does not mean the others share the fault. Note the room and unit address so the technician goes straight to the right head.
Bulkhead and floor console models follow the same logic too. Wherever the coil sits, the liquid pipe sensor is clipped to it and wired to that unit’s own board. The repair approach does not really change, only the panels that need removing first.
Prevention
Can Regular Servicing Prevent P2?
No service can make a sensor last forever. However, good maintenance reduces the stresses that shorten its life. A clean coil runs at a more stable temperature and sheds condensate properly, which keeps the sensor area drier.
During a routine service, a technician typically cleans filters, washes the coil where appropriate, checks the drain and looks over visible wiring. While the panels are off, a loose sensor holder or a stretched lead is easy to spot and fix. Catching those small issues early can prevent a breakdown on the hottest day of the year.
Between services, monthly filter cleaning during heavy use is the best habit you can build. It keeps air moving across the coil, so the coil is less likely to run overly cold and wet. That is good for the sensor and good for your comfort.
Safety
Can I Keep Running My Air Conditioner With P2?
In most cases the unit simply refuses. It stops to protect the coil, because it cannot detect icing or overheating without the liquid pipe reading.
Forcing repeated restarts is not a good idea. If the sensor is intermittent, the system may run for a while without full coil protection. That risks ice forming on the coil in cooling, which can then melt and overflow the drain tray later.
The safer approach is to switch the unit off at the breaker and book a visit. P2 rarely signals danger, but it does signal that the system is running blind on one of its key inputs.
Australian Climate
Does Humidity Make P2 More Likely?
It can. The liquid pipe sensor lives on a cold, wet surface during summer. In humid cities like Brisbane, and during sticky Sydney spells, the indoor coil produces a lot of condensate. Over years, that moisture can wick into the sensor plug and cause corrosion.
Heavy cooling seasons add more cycles too. A long Perth or Adelaide summer means the coil swings between cold running and warm standby many times a day. Each swing flexes the sensor lead slightly, which can eventually break fine copper strands inside the insulation.
Dust plays a smaller role. A dusty coil holds more moisture and runs colder, which speeds up the same wear. Regular filter cleaning and a periodic professional service keep the coil drier and give sensors a longer life.
Comparing Codes
How Is P2 Different From Other Mitsubishi Sensor Codes?
Mitsubishi Electric uses several sensor codes that sound alike. Understanding the differences helps you follow the technician’s explanation.
P1 Versus P2
P1 concerns the room intake sensor, which reads the air entering the unit. P2 concerns a coil pipe sensor. Both are sensor circuit faults, but on different parts with different jobs. Read more on the Mitsubishi P1 page.
P2 Versus P9
P9 relates to the sensor on the two phase section of the coil, often labelled TH5. Both plug into the same area of the board, which is why they can share a lamp pattern.
See every confirmed code on our Mitsubishi error codes hub, or compare with other brands in the full error code library.
Getting Help
Where Can I Book a P2 Repair?
Rapid Air Cooling arranges repairs across Australia’s major capitals. We take the booking, then send an independent licensed technician. We are not a Mitsubishi dealer and make no claim of manufacturer accreditation.
Choose your city to get started. Sydney households can visit our Sydney repairs page. For Victoria, use Melbourne air conditioner repairs. Brisbane residents have repairs in Brisbane, Perth has Perth air conditioner repairs, and Adelaide has repairs around Adelaide.
For brand advice, see our Mitsubishi air conditioning page or a local page like Mitsubishi in Brisbane. Our troubleshooting section covers other symptoms, and you can read about our air conditioning service Australia wide.
Good to Know
What Else Should I Know About Coil Sensors?
Open more detail
Coil sensors usually sit in a small metal holder or pocket on the pipe. If the holder loosens, the sensor may read air temperature rather than pipe temperature. That will not always trigger P2, but it can cause odd behaviour, so the technician checks the holder as part of any coil sensor job.
Some technicians apply a little thermal paste when refitting a sensor. This improves contact with the pipe and gives a more accurate reading. It is a small detail, yet it can prevent future comfort complaints.
On ducted systems, the indoor unit often sits in the roof space. Summer roof temperatures in Australia can be extreme, so technicians usually prefer morning appointments for ducted coil work. Safe roof access, with a sturdy ladder point and clear path, makes the visit much smoother.
It is also worth knowing that a sensor fault can hide behind a sound refrigerant system. Once the new thermistor is fitted, the unit usually returns to normal operation straight away. If it does not, the technician moves on to the board and the remaining wiring with a clear, tested baseline.
Lastly, remember that not every part is interchangeable. Even within Mitsubishi Electric, sensor lengths, plugs and resistance curves vary between ranges. The technician will match the part to your model number.
Questions
Frequently Asked Questions
Does P2 mean my coil is frozen?
Not directly. P2 means the coil sensor reading is impossible. A frozen coil is more closely linked to P6. However, running a unit without coil protection can lead to icing, which is another reason to book promptly.
Why does P2 come and go with the weather?
Moisture is the usual reason. A slightly corroded or loose plug may lose contact on humid days and recover when it dries. That pattern points to a connection fault rather than a dead sensor.
Can I tell P2 from P9 using the lamp?
On some ranges you cannot, because both use a two flash pattern. A wired controller, the error history or a technician’s check will show which sensor is responsible.
Is P2 used by Mitsubishi Heavy Industries?
Not with this meaning. MHI uses numbered E codes. If your unit says Mitsubishi Heavy Industries on the badge, look up its own code list instead.
Will cleaning the coil fix P2?
Cleaning will not repair a failed sensor or plug. It does reduce moisture and stress on the coil, so it is good maintenance after the repair.
Is the P2 sensor expensive to replace?
A thermistor is a small part compared with boards or compressors. The total cost depends on access, especially for ducted units in the roof. The technician will explain before starting work.
Need Help With a P2 Code?
Call with your model number and we will book a licensed technician to test the coil sensor circuit.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles