Trane mini split error code P4
2 meanings on Trane, depending on which series you have. Check the model number on the indoor unit's label.
If yours is a 4TXK / 4MXW series unit
Excessive outdoor discharge temperature.
- TypeProtection
- SystemCompressor / inverter
- Can I fix it?Homeowner checks, then maybe a tech
What P4 means on a Trane
The refrigerant leaving the compressor got too hot. The compressor stops to protect itself.
On this platform, P4 is a protection: the system stopped or throttled itself to prevent damage; many clear on their own once conditions return to normal.
Common causes
- Low refrigerant charge.
- A blocked outdoor coil or failed fan.
- A partly closed service valve.
- A failing compressor.
How to fix it yourself
Work through the checks below first; they resolve most cases. If they do not, the repair itself may need a technician.
- Look at the outdoor unit: clear leaves, cottonwood fluff, snow or ice from the coil and make sure the fan can spin freely and nothing is stacked against the cabinet.
- Confirm the service valves are fully open.
- Cool down with power off for 30 minutes and retry.
- Anything inside the refrigerant circuit (sensors are fine, but valves, compressors and leaks are not) needs EPA-certified refrigerant handling. That is a technician job.
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
Recurring P4 with a clean coil needs a charge check.
If yours is a Trane-Mitsubishi Electric NTX series unit
Drain sensor or float switch fault.
- TypeFault
- SystemCondensate drain
- Can I fix it?Usually a homeowner fix
What P4 means on a Trane
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 Trane units show P4
Trane sells 4TXK / 4MXW hi-wall inverter, 4TYK / 4MYW and Trane-Mitsubishi Electric NTX series units, and this code carries more than one meaning across them: on the 4TXK / 4MXW series, P4 means excessive outdoor discharge temperature; on the Trane-Mitsubishi Electric NTX series, P4 means drain sensor or float switch fault. The model number on the indoor unit's label, and which display you are reading, tell you which applies.
Where Trane shows this code
4TXK / 4MXW series: The indoor display shows the code in place of the set temperature. E codes are faults: something has failed and needs diagnosis. P, H, d and F codes are protections: the system stopped or throttled itself to prevent damage, and many clear on their own once conditions return to normal.
Trane-Mitsubishi Electric NTX series: 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 Trane 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
- Mitsubishi Electric P4 Drain sensor or float switch fault
- ACiQ P4 Inverter compressor drive error / Excessive outdoor discharge temperature
- American Standard P4 Excessive outdoor discharge temperature / Drain sensor or float switch fault
Questions people ask
Why does P4 have more than one meaning on a Trane?
Trane sells units built on more than one control platform, and each platform has its own code table. The model number on the indoor unit's label tells you which series you have: 4TXK / 4MXW series units read P4 as excessive outdoor discharge temperature; Trane-Mitsubishi Electric NTX series units read P4 as drain sensor or float switch fault.
Can I reset a Trane 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 Trane showing P4?
Not repeatedly. A protection code means the unit stopped itself to prevent damage, and resetting it over and over can turn a cheap repair into a compressor failure. Reset once, check the basics, and stop if it returns.
Sources
- Trane Mini Split HW Inverter Service Manual (4TXK / 4MXW), SVM027A-EN, 2024, error code table
- Mitsubishi Electric M-Series 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.