What does error code E4 mean on a Mitsubishi Electric mini-split?

Wired remote communication error. Communication error between the wired remote controller and the indoor unit.

Can I fix Mitsubishi Electric code E4 myself?

Start with these safe checks: Turn the system's breaker off for a few minutes and back on. If it returns, call an HVAC technician to check the remote wiring.

When should I call a technician for code E4?

If it returns, call an HVAC technician to check the remote wiring. Don't open the sealed refrigerant system, cut or braze lines, or add refrigerant. That needs an EPA-certified technician. Turn power off at the breaker or disconnect before opening any panel, and leave capacitors, compressors and control boards to a pro: they can hold a dangerous charge even with the power off.

Mitsubishi Electric Mini-Split Error Code E4 / E5 / 9 blinks:…

What E4 means

Communication error between the wired remote controller and the indoor unit.

Also shown as: E5, 9 blinks, depending on the model.

Likely causes

Loose remote wiring
Remote or board fault

Safe first checks

Turn the system's breaker off for a few minutes and back on.

When to stop

If it returns, call an HVAC technician to check the remote wiring.

Checked against: Mitsubishi Electric, Mr. Slim indoor/outdoor unit malfunction-diagnosis check codes (2024-11-18). Codes can differ by model and year, so confirm with your owner's manual.