Mitsubishi Electric Mini-Split Code E4
Soft lockout
Remote controller signal receiving error detected by the indoor unit. The indoor controller board received no data from the remote controller board for 3 minutes (or no signal at all for 2 minutes).
Manual wording: “Abnormal if indoor controller board cannot receive any data normally from remote controller board or from other indoor controller board for 3 minutes. (Check code: E4)”
Documented for: A-Control systems with a wired remote controller
Likely causes, most common first
- Contact failure at the remote controller transmission wire
- All remote controllers set as 'sub'
- Miswiring of the remote controller
- Defective transmitting/receiving circuit of the remote controller or indoor controller board
- Noise on the remote controller transmission wire
What you can safely check yourself
- Turn the system off at the breaker, wait one minute, and turn it back on once
When to call a technician
Remote controller wiring and main/sub addressing are technician tasks.
A Mitsubishi Electric mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- Indoor Unit Service Manual No. OCH761 Revised Edition-A - PKA-A LA Series (May 2021) (Mitsubishi Electric, PKA-A12LA, PKA-A18LA, PKA-A12LA.TH, PKA-A18LA.TH wall-mounted indoor units) · checked 2026-08-25
- Service Manual No. OCH750 Revised Edition-E - PUZ-HA Outdoor Units (May 2024) (Mitsubishi Electric, PUZ-HA24NHA1, PUZ-HA30NKA, PUZ-HA36NKA, PUZ-HA42NKA1 heat-pump outdoor units) · checked 2026-08-25