Mitsubishi Error Code P6 (4102): Open Phase / Power Supply Fault

Quick Answer — Mitsubishi Error Code P6 (4102)

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Error code P6 on Mitsubishi CITY MULTI systems means an open-phase or power-supply fault at the outdoor unit.

The inverter detects unstable or missing power on one line and shuts down the compressor to avoid electrical damage.

Common causes include missing phase (45 %), loose wiring or terminal damage (30 %), and voltage imbalance (15 %).

It’s critical to power off the system immediately and verify supply voltage with a multimeter.

Typical repair cost: $350 – $700, rising to $1 800 if the inverter PCB is damaged.

For professional diagnosis, book Fixair same-day service — most P6 cases are resolved within 24 hours.

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What P6 Means

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The P6 fault (4102) is a power-input error. Mitsubishi outdoor units continuously monitor three-phase voltage to protect the inverter module and compressor.

If one phase drops or voltage becomes unbalanced beyond ±10 %, the controller stops operation and logs code P6.

This safeguard prevents severe inverter or motor burnout.

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Main Causes of P6

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1. Missing Phase (≈ 45 %) — One supply line open due to blown fuse or utility issue.
2. Loose or Burned Connection (≈ 30 %) — Terminal block corrosion or vibration damage.
3. Voltage Imbalance (≈ 15 %) — Uneven line voltages > 10 % difference.
4. Faulty Inverter Power Module (≈ 10 %) — IGBT or IPM damage after surge.

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Immediate Safety Steps

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1. Disconnect power to the outdoor unit.
2. Inspect breaker, fuses, and terminal screws for discoloration or burning.
3. Measure all three-phase voltages (L1-L2-L3) — they must be balanced within ±10 %.
4. If voltage is unstable, contact your electrical provider.
5. Do not reset the controller until the power fault is corrected.
6. Call Fixair for full electrical and inverter-board diagnostics.

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Repair Costs (2025)

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Most P6 repairs average $350 – $700, covering diagnostic time, wiring repair, and power checks.

If inverter damage occurred, costs may rise to $1 200 – $1 800 due to board replacement and testing.

Total service time typically ranges from 2 to 4 hours.

Technicians also verify grounding, fuses, and phase balance before resetting the controller.

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Prevention Tips

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• Verify three-phase voltage balance during each maintenance visit.
• Tighten electrical connections annually to prevent heat damage.
• Use surge protection and phase-failure relays on commercial installations.
• Schedule yearly electrical inspections to avoid repeated P6 faults.

Preventive maintenance eliminates ≈ 80 % of P6 occurrences.

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Frequently Asked Questions

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Is error P6 dangerous?

Yes. An open phase can overheat the compressor and destroy inverter components within minutes.

Can I reset it myself?

Only after confirming stable three-phase voltage. Otherwise, the fault will return immediately.

How much does it cost to fix?

Between $350 and $700 for power-supply repairs; up to $1 800 if the inverter board is replaced.

How long does repair take?

2 – 4 hours for diagnosis and repair, depending on site access and spare parts.

Will it come back?

Not if line voltage remains stable and connections are retorqued during annual service.

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Summary

Error code P6 (4102) means the Mitsubishi outdoor unit has detected an open phase or power-supply fault. It protects the inverter by immediately stopping operation.

Check supply voltage, tighten connections, and have a professional verify power balance before restart.

Most repairs are completed the same day for under $700.

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