Mitsubishi Electric P4 error code

What it means

P4 means the indoor unit sees a drain, drain-sensor, or indoor valve signal problem. If water cannot leave the unit or a drain sensor cannot be trusted, the system may stop to prevent overflow or abnormal operation. Check for visible water or a blocked drain outlet only from outside the cabinet. Manual trigger: Drain sensor connector CN1S1 is open for more than 3 minutes.

Urgency

Likely causes

1. Temperature sensor reading out of range
2. Loose sensor connector or damaged sensor lead
3. Moisture, corrosion, or vibration affecting the sensor circuit
4. Control board input fault after the sensor checks out

Homeowner fix

If you see water at the indoor head, turn the system off. Check only for an obvious blocked drain outlet or overflowing pan; if water is present or the code remains, leave it off.

When to call a pro

Call a licensed HVAC technician if water is present, the indoor head is dripping, or the code returns. Tell them the code points to the drain sensor, drain pump, or indoor LEV/drain circuit.

Repair vs replace

Drain and condensate faults are usually repairable and are rarely a reason to replace the whole mini split. Replacement only becomes relevant if water damage, age, and other major failures are already part of the picture.

• Mitsubishi Electric M-Series GX 9,000 BTU R-454B 208/230V (MSZ-GX09NL / MUZ-GX09NL)

  M-Series GX

• Mitsubishi Electric M-Series GX Hyper-Heat 9,000 BTU R-454B 208/230V (MSZ-GX09NL / MUZ-GX09NLHZ)

  M-Series GX

• Mitsubishi Electric M-Series GX 12,000 BTU R-454B 208/230V (MSZ-GX12NL / MUZ-GX12NL)

  M-Series GX

• Mitsubishi Electric M-Series GX Hyper-Heat 12,000 BTU R-454B 208/230V (MSZ-GX12NL / MUZ-GX12NLHZ)

  M-Series GX

Parts for this line

The parts catalog for Mitsubishi Electric M-Series GX lists 6 sourced replacement parts for this product line.

For your technician

Technician note: inspect condensate drainage, drain sensor/pump connector, indoor LEV where applicable, and indoor P.C. board inputs. Page context: Mitsubishi Electric maps this display to the M-Series GX line; source: Mitsubishi Electric MSZ-GX/MUZ-GX R454B service manuals; display convention: match the letter P and four marker exactly before comparing neighboring codes.

Which systems show it

• Mitsubishi Electric MSZ-GX R454B wall-mounted indoor units covered by OBH950B; common M-Series wall-mount diagnostics apply where matched by model manual.

Related troubleshooting

Use the symptom guide alongside the exact display code if the unit is flashing, cycling, or showing comfort symptoms.

Reset note

After the documented cause is corrected, operate the unit and confirm the failure-mode recall/error-code display returns to 00.

Manual trigger

Drain sensor connector CN1S1 is open for more than 3 minutes.

Related codes

Source

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