Mitsubishi Electric mini split error code P4
Drain sensor or float switch fault.
- TypeFault
- SystemCondensate drain
- Can I fix it?Usually a homeowner fix
What P4 means on a Mitsubishi Electric
The drain-level sensor or float switch reports the condensate level is too high, or the sensor itself has failed. The unit stops cooling to avoid an overflow.
On this platform, P4 is a fault: something has failed or is disconnected and needs diagnosis.
Common causes
- A blocked or kinked condensate drain.
- A drain line without continuous fall.
- A failed condensate pump.
- A dirty or failed drain sensor.
How to fix it yourself
You can almost always clear this yourself with the steps below.
- Confirm water flows from the drain outlet while cooling.
- Clear the drain with a wet/dry vacuum at the outlet.
- Check the drain line for dips.
- If a pump is fitted, check it runs and the float moves freely.
Switch off power at the breaker before opening either unit. Capacitors in the outdoor unit hold a charge for several minutes after power is cut.
When to call a technician
A technician can replace a failed pump or sensor.
Which Mitsubishi Electric units show P4
This page applies to Mitsubishi Electric M-Series (MSZ), Mr. Slim (PKA/PCA), Hyper-Heating H2i and MXZ multi-zone units. Mitsubishi Electric's own documentation lists P4 as "Drain sensor or float switch fault", the same definition used across the Mitsubishi Electric it is built on. If your unit shows a code with a different shape (for example a four-character code, or a plain number), it is from a different table; use the lookup with your exact code.
Where Mitsubishi Electric shows this code
Wall units without a wired controller signal a fault by blinking the operation indicator lamp; the code itself shows on a wired controller (MHK/PAR series) or on the wireless remote after entering its check mode (see your manual). On the outdoor unit, the control board LEDs blink the same code. P codes are indoor-unit faults, E codes are communication faults, F codes are outdoor-unit faults and U codes are outdoor-unit and compressor faults.
Other Mitsubishi Electric codes
Same part of the system as P4:
P4 on other brands
The same characters do not always mean the same thing. Check the brand on your unit.
- Pioneer P4 Inverter compressor drive error / Compressor discharge temperature protection (outdoor display)
- Blueridge P4 Inverter compressor drive error
- Zone Air P4 Excessive outdoor discharge temperature
- Daikin P4 Inverter heat sink temperature sensor fault
- Trane P4 Excessive outdoor discharge temperature / Drain sensor or float switch fault
- ACiQ P4 Inverter compressor drive error / Excessive outdoor discharge temperature
Questions people ask
Can I reset a Mitsubishi Electric P4 code myself?
Yes. Turn the system off at the breaker for five minutes, then restart it. If P4 comes back, the fault is real and needs the checks above.
Is it safe to keep running a Mitsubishi Electric showing P4?
The unit will usually refuse to run, or run with reduced output, until the fault is cleared. Repeated resets do not fix anything and can mask a problem that is getting worse.
Do I need a technician for Mitsubishi Electric P4?
You can almost always clear this yourself with the steps below. A technician can replace a failed pump or sensor.
Sources
- Mitsubishi Electric M-Series and Mr. Slim service manuals (self-diagnosis tables)
Updated September 2026. Codes and definitions vary by model year. If your manual disagrees with this page, your manual wins. Send a correction.