Mitsubishi Electric mini split error code E4
Indoor unit signal receiving error (from remote controller).
- TypeFault
- SystemCommunication
- Can I fix it?Homeowner checks, then maybe a tech
What E4 means on a Mitsubishi Electric
The indoor unit is not receiving data from the wired remote controller.
On this platform, E4 is a fault: something has failed or is disconnected and needs diagnosis.
Common causes
- A loose or damaged controller cable.
- A failed controller or indoor board.
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.
- Reset the system: switch the breaker (or the outdoor disconnect) off, wait a full five minutes so the boards fully discharge, then switch it back on and restart from the remote.
- Reseat the controller cable.
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
Technician check.
Which Mitsubishi Electric units show E4
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 E4 as "Indoor unit signal receiving error (from remote controller)", 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 E4:
E4 on other brands
The same characters do not always mean the same thing. Check the brand on your unit.
- Pioneer E4 Indoor room temperature sensor (T1) open or short circuit / Outdoor temperature sensor fault: coil (T3), ambient (T4), discharge (T5) or a zone coil outlet (T2B)
- Blueridge E4 Compressor discharge temperature too high / Indoor room temperature sensor (T1) open or short circuit
- Gree E4 Compressor discharge temperature too high
- Zone Air E4 Abnormal system operation or lack of refrigerant
- Daikin E4 Low pressure protection
- Carrier E4 Indoor room temperature sensor (T1) open or short circuit
- Trane E4 Abnormal system operation or lack of refrigerant / Indoor unit signal receiving error (from remote controller)
- Heil E4 Indoor room temperature sensor (T1) open or short circuit / Compressor discharge temperature too high
- ACiQ E4 Indoor room temperature sensor (T1) open or short circuit / Abnormal system operation or lack of refrigerant
Questions people ask
Can I reset a Mitsubishi Electric E4 code myself?
Yes. Turn the system off at the breaker for five minutes, then restart it. If E4 comes back, the fault is real and needs the checks above.
Is it safe to keep running a Mitsubishi Electric showing E4?
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 E4?
Work through the checks below first; they resolve most cases. If they do not, the repair itself may need a technician. Technician check.
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.