Mitsubishi MSZ-FS06NA 6,000 BTU Compact Wall-Mount Indoor Unit E4 Error Fix: Indoor Unit PCB Processor Error

Error code E4 on the Mitsubishi MSZ-FS06NA 6,000 BTU Compact Wall-Mount Indoor Unit means: Indoor Unit PCB Processor Error. The main microprocessor on the indoor unit control board has failed or is not functioning correctly. The PCB may have sustained damage from a power surge, lightning strike, or moisture intrusion. Try resetting power to the indoor unit at the breaker for 30 seconds. If E4 recurs, the indoor unit PCB requires replacement. This is not a field-repairable component — order the model-specific PCB from Mitsubishi Electric parts.

The most successful fix is "Replace the Indoor Unit PCB Control Board" (hard difficulty, ~90 minutes). Estimated DIY cost: $0-$20. HomeMD has 2 community-ranked fixes for this error.

This error is rated critical severity. It is generally not urgent and can often be resolved with a simple DIY fix.

Yes — the top-ranked community fix ("Replace the Indoor Unit PCB Control Board") is rated hard difficulty and takes about 90 minutes. Tools needed: T20 Torx screwdriver, Multimeter, Anti-static wrist strap.

DIY cost: $0-$20. Professional repair typically costs $300-$450. Many homeowners save money by trying the top-ranked community fix first.

The Mitsubishi MSZ-FS06NA 6,000 BTU Compact Wall-Mount Indoor Unit has 8 other known error codes, including: E1 (Remote Controller PCB Error), E2 (Remote Controller Signal Receiving Error), E3 (Remote Controller Communication Error), E5 (Indoor/Outdoor Communication Error (Legacy)), E6 (Indoor Unit EEPROM Error), and 3 more.

Error code E4 also appears on 8 other Mitsubishi models: MLZ-KP09NA 9,000 BTU One-Way Ceiling Cassette Indoor Unit, MSZ-EF15NA 15,000 BTU Designer Series (Kirigamine Zen) Wall-Mount Indoor Unit, MSZ-FH12NA 12,000 BTU Hyper-Heat H2i Wall-Mount Indoor Unit, MSZ-GL09NA 9,000 BTU Wall-Mount Ductless Mini-Split Indoor Unit, MSZ-GL12NA 12,000 BTU Wall-Mount Ductless Mini-Split Indoor Unit, SEZ-KD12NA 12,000 BTU Ceiling-Concealed Ducted Indoor Unit, and 2 more. The fix may vary by model, so check each model's specific page for tailored repair steps.