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Pioneer Diamante / Quantum Error Codes
Older Pioneer lines (Diamante WYT-19/22 and Quantum WYS) use different meanings for some codes. This table is Pioneer's current Diamante and Quantum chart.
| Code | Meaning | What to check |
|---|---|---|
| bc | PM2.5 sensor fault, indoor unit (optional feature). | How to fix → |
| bd | Fresh air fan motor fault. | |
| bE | CO2 sensor fault, indoor unit (optional feature). | How to fix → |
| bf | TVOC sensor fault, indoor unit (optional feature). | How to fix → |
| bj | Humidity sensor fault, indoor unit. | |
| CL | Air filter cleaning reminder (not an error). | Clean the filters and reset the reminder. |
| d4 | Drain pan full protection. | Plugged drain, condensate pump, float switch. |
| d5 | Access control signal protection. | Key card / door contact input on the board. |
| dF | Defrost mode (not an error). | Normal in heating. |
| E0 | Communication fault between indoor and outdoor units. | Interconnect wiring, connections, outdoor power. How to fix → |
| E1 | Indoor room temperature sensor fault. | Measure the sensor; check connector. How to fix → |
| E2 | Indoor coil temperature sensor fault. | Measure the sensor; check connector. How to fix → |
| E3 | Outdoor coil temperature sensor fault. | Measure the sensor; check connector. How to fix → |
| E4 | System abnormality or refrigerant shortage. | Leak search, service valves open, restriction. How to fix → |
| E5 | Model configuration mismatch (production line testing only). | |
| E6 | Indoor DC fan fault. | Fan motor, wheel binding, connector. |
| E7 | Outdoor ambient temperature sensor fault. | Measure the sensor; check connector. How to fix → |
| E8 | Outdoor discharge temperature sensor fault. | Measure the sensor; check connector. How to fix → |
| E9 | Outdoor IPM or compressor drive fault. | Supply voltage, compressor wiring and windings, drive board. How to fix → |
| EA | Outdoor current sensor fault. | Outdoor board. How to fix → |
| Eb | Communication fault between indoor main board and display board. | Display cable and connectors. |
| EC | Outdoor module communication fault. | Board-to-board connections in the outdoor unit. |
| EE | Outdoor EEPROM fault. | Outdoor board. |
| EF | Outdoor DC fan motor fault. | Fan obstruction, motor, connector. |
| EH | Outdoor suction temperature sensor fault. | Measure the sensor; check connector. How to fix → |
| Ej | Outdoor mid-coil temperature sensor fault. | Measure the sensor; check connector. How to fix → |
| En | Outdoor gas pipe temperature sensor fault. | Measure the sensor; check connector. How to fix → |
| EP | Outdoor compressor top temperature sensor fault. | Measure the sensor; check connector. How to fix → |
| EU | Outdoor voltage detection circuit abnormality. | Supply voltage; outdoor board. How to fix → |
| Ey | Outdoor liquid pipe temperature sensor fault. | Measure the sensor; check connector. How to fix → |
| F0 | Indoor infrared sensor fault. | How to fix → |
| F1 | Indoor power detection module fault. | |
| F2 | Outdoor discharge temperature sensor fault protection. | Measure the sensor; check connector. How to fix → |
| F3 | Outdoor coil temperature sensor fault protection. | Measure the sensor; check connector. How to fix → |
| F4 | Abnormal refrigerant flow protection. | Restriction, closed valve, low charge. How to fix → |
| F5 | Outdoor PFC protection. | Supply voltage stability; outdoor board. How to fix → |
| F6 | Compressor phase loss or phase reversal protection. | Compressor U-V-W wiring, drive board. How to fix → |
| F7 | Outdoor IPM abnormal temperature protection. | Outdoor airflow, heat sink mounting. How to fix → |
| F8 | Outdoor 4-way valve reversing abnormality. | Coil voltage, valve operation, pressures. |
| F9 | Outdoor IPM temperature sensor fault. | Outdoor board. How to fix → |
| FA | Outdoor compressor phase current detection circuit failure. | Outdoor board. |
| Fb | Cooling or heating overload frequency limit (protective slowdown). | Check airflow and charge if it persists. |
| FC | Frequency reduced due to high power consumption. | Status; check supply and load if it persists. |
| Fd | Refrigerant leak sensor communication fault. | Leak sensor wiring and module. |
| FE | Outdoor IPM or compressor phase overcurrent protection. | Compressor windings, wiring, refrigerant system, drive board. How to fix → |
| FF | Frequency reduced due to high IPM temperature. | Outdoor airflow, dirty coil. How to fix → |
| FH | Frequency reduced due to compressor drive limit. | Status. How to fix → |
| Fj | Frequency reduced due to high discharge temperature. | Low charge or restriction. How to fix → |
| Fn | Frequency reduced due to high AC input current. | Supply voltage, dirty coils. How to fix → |
| FP | Frequency reduced to prevent condensation. | Status. |
| FU | Frequency reduced to prevent coil freezing. | Airflow: filters, fan, coil. |
| Fy | Refrigerant deficiency protection. | Leak search; charge by weight. How to fix → |
| H1 | Outdoor high-pressure switch fault. | Dirty coil, fan, overcharge, switch wiring. |
| H2 | Outdoor low-pressure switch fault. | Low charge, restriction, switch wiring. How to fix → |
| Hd | Refrigerant leak protection. | Find and repair the leak. How to fix → |
| P0 | Outdoor IPM protection. | Supply voltage, outdoor airflow, compressor, drive board. How to fix → |
| P1 | Overvoltage or undervoltage protection. | Supply voltage under load. How to fix → |
| P2 | Overcurrent protection. | Compressor, refrigerant system, supply voltage. How to fix → |
| P4 | Outdoor high discharge temperature protection. | Low charge, restriction, discharge sensor. How to fix → |
| P5 | Overcooling protection in cooling or dry mode. | Low airflow or low charge. |
| P6 | Overheat protection in cooling mode. | Dirty outdoor coil, fan, high ambient, overcharge. |
| P7 | Overheat protection in heating mode. | Indoor airflow (filters, fan), overcharge. |
| P8 | Outdoor ambient temperature too high or too low. | Outside the unit's operating range. |
| P9 | Outdoor compressor drive overload protection. | Compressor, wiring, drive board. How to fix → |
| PA | Mode conflict (multi-zone) or indoor upper airflow module communication fault. | Set all heads to the same mode. |
How to read the codes
- CL (filter reminder), dF (defrost) and the F codes that say 'frequency reduced' are status messages: the unit is protecting itself and keeps running.
- 0A on the display means Generator mode, not a fault.
- Match the code exactly, including upper and lower case.
Codes point to a circuit, not a part. Test before replacing boards or sensors. Inverter boards hold a dangerous charge after power-off; wait and verify DC bus voltage is gone before touching them. Refrigerant work requires EPA 608 certification.
Source: Pioneer Support: Error Code Table for Diamante & Quantum Series Systems. The "meaning" column follows the manufacturer's wording; "what to check" is our field summary. Always go by the label on the furnace you're working on.
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