Mitsubishi Electric Mini-Split Code E9
Soft lockout
Indoor/outdoor unit communication error - transmitting error detected by the outdoor unit. The outdoor controller board could not find a free slot on the transmission path for 3 minutes.
Manual wording: “E9 Indoor/outdoor unit communication error - Transmitting error (Indoor unit)”
Documented for: A-Control outdoor units (PUZ, MUZ, MXZ)
Likely causes, most common first
- Indoor/outdoor unit connecting wire has contact failure or is miswired
- Defective communication circuit of the outdoor controller board
- Defective communication circuit of the indoor controller board
- Noise has entered the power supply or the indoor/outdoor connecting wire
What you can safely check yourself
- Check that the breaker feeding the outdoor unit is on and has not tripped
- Turn the system off at the breaker, wait one minute, and turn it back on once
When to call a technician
Connecting-wire and board work is a technician job.
A Mitsubishi Electric mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- 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