Fujitsu Mini Split Diagnostic Error Codes

Fujitsu mini splits (Halcyon, ASY/ASU series, DLF series) store diagnostic trouble codes as 2-digit numbers. These codes are separate from the E-codes and P-codes that display automatically on the remote. You have to enter diagnostic mode to read them. The system records the most recent fault in memory, so even if the unit is running again, you can still pull the code.

How to Enter Diagnostic Mode on a Fujitsu Mini Split

To access the diagnostic codes, press and hold the RESET button and the TEST RUN button on the remote control simultaneously for 3-5 seconds. The indoor unit LED display shows a two-digit code.

On Fujitsu Halcyon models with a wired remote controller, press the TEST button three times within 5 seconds of turning the unit on. The display shows the most recent fault code.

To clear the code after repair: power cycle the unit from the breaker for 60 seconds. For wired controllers, press the TEST button again while the code is displayed to reset the error history.

Error Code Reference Table

Code	Fault	Likely Cause	LED Pattern (Power / Timer)
01	Indoor-outdoor communication fault	Open/short in signal wire, loose terminal, failed outdoor PCB	Power: 1 blink/sec
02	Polarity/phase reversal	Line and neutral swapped at outdoor unit	Power: 2 blinks/sec
03	Power supply voltage fault	Voltage outside range (187-253V)	Power: 3 blinks/sec
04	Indoor room temperature sensor fault	NTC thermistor open or shorted	Timer: 2 blinks on, 2 off
05	Indoor coil temperature sensor fault	Coil thermistor open or shorted	Timer: 3 blinks on, 3 off
06	Outdoor thermistor fault	Outdoor ambient or pipe sensor	Timer: 4 blinks on, 4 off
07	Compressor fault	No rotation, locked rotor, winding fault, inverter failure	Power + Timer: fast flash
08	Outdoor fan motor fault	Hall sensor failure, motor seized	Power: 5 blinks on, pause
09	EEPROM / PCB fault	Control board memory error	Power + Timer: alternating blinks
10	Valve/4-way valve fault	Reversing valve stuck or short cycling	Timer: continuous slow flash
11	Drain pump / float switch fault	Float stuck, pump failed, drain line clogged	Power: 1 blink, Timer: 1 blink
12	Overcurrent protection	Compressor current exceeds rating	Power: fast flash
13	Discharge temperature high	Low refrigerant or blocked EEV	Timer: fast flash
14	High pressure switch open	Condenser coil dirty or fan not running	Power + Timer: both solid
15	Low pressure switch open	Refrigerant leak or restriction	Power + Timer: both fast flash

Code 01: Communication Fault Between Indoor and Outdoor Units

Code 01 means the indoor unit lost communication with the outdoor unit. This is the most common diagnostic code on Fujitsu mini splits.

Check the interconnecting cable first. Fujitsu uses a 3-conductor cable: L (line), N (neutral), and S (signal). The S wire carries serial communication between the two PCBs. Open the electrical covers on both units and verify each wire is tight at its terminal. Loose S-wire connections cause intermittent code 01 faults that appear and disappear as the unit vibrates.

The signal cable must be a twisted, shielded pair when running alongside power wiring. Running unshielded communication wire in the same conduit as line voltage causes induced noise that the PCB interprets as a communication loss. If the cable runs are longer than 100 feet, downsize to 16 AWG max or use a field-supplied communication booster.

After confirming wiring, check the outdoor PCB fuse. A blown fuse on the outdoor board kills the control circuit and prevents communication. The fuse is typically a 6.3A or 10A blade fuse on the outdoor PCB. Test for continuity. If blown, replace, then look for what caused it to blow before powering up again.

If wiring and fuses check out, the outdoor PCB has failed. Replace it with the Fujitsu OEM part for your model.

Code 04: Indoor Room Temperature Sensor Fault

Code 04 indicates the NTC thermistor behind the indoor unit’s return air grille has gone open or shorted. The room temperature sensor communicates air temperature back to the indoor PCB for setpoint control.

To test: remove the front grille and locate the small thermistor clipped into the air inlet area. Unplug the connector from the indoor PCB. Measure resistance across the two pins with a multimeter. At 77F (25C), a healthy Fujitsu thermistor reads 10 kOhm, give or take 5%. Measure the temperature at the sensor location with an independent thermometer and compare.

The resistance table for a standard Fujitsu 10K NTC thermistor:

At 50F (10C): approximately 19.9 kOhm
At 77F (25C): approximately 10.0 kOhm
At 95F (35C): approximately 6.5 kOhm
At 130F (55C): approximately 4.1 kOhm

If resistance is more than 15% off from the spec at a known temperature, replace the thermistor. If resistance is infinite (open) or zero (shorted), replace the thermistor.

Code 05: Indoor Coil Temperature Sensor Fault

Code 05 is the indoor coil thermistor (evaporator temperature sensor). This sensor is clipped into the copper tubing of the indoor coil. Testing is the same as code 04: disconnect, measure resistance, compare to the 10K NTC table above.

A failed indoor coil sensor causes the unit to run wild because the PCB loses its evaporator temperature feedback. In cooling mode, the unit may freeze the coil. In heating mode, it may short-cycle on high pressure.

Code 07: Compressor Fault

Code 07 means the outdoor inverter PCB detected a compressor problem. The system shuts down the compressor and displays the code on the indoor unit.

Start with easy checks first. Verify the outdoor unit has full power. Measure voltage at the L1-L2 terminals at the outdoor disconnect. You need 208-240V, plus or minus 10%. Check that all three phase legs (if a 3-phase unit) are present and balanced. Listen for the contactor pulling in.

Next, test the compressor windings. With the unit powered off and capacitors discharged, disconnect the compressor terminals (U, V, W). Measure resistance between each pair of terminals. All three readings should match within 5%. A short between any terminal and ground (bare copper tube on the compressor shell) means the windings have failed.

If the windings test good but code 07 persists, the inverter board (IPM module on the outdoor PCB) has failed. The Intelligent Power Module converts DC bus voltage to 3-phase AC for the compressor. A failed IPM triggers code 07 even when the compressor itself is fine.

One more thing about code 07: after any power interruption, the unit waits 3 minutes before restarting the compressor. The built-in restart delay protects the compressor from short-cycling against high-side pressure. Do not interpret this delay as a problem.

Code 11: Drain Pump / Float Switch Fault

Code 11 appears on units with a condensate drain pump (common in basement or concealed installations where gravity drainage is unavailable). The indoor PCB detected the float switch in the drain pan remained open for too long, or the drain pump failed to activate.

Check the drain pan first. Remove the front panel and look at the water level in the condensate pan. If water is overflowing the pan, the drain line is clogged. Use a wet-dry vacuum to clear the drain line from the exterior end. Flush with a 50/50 vinegar-water mix to kill algae growth.

If the pan is empty but the code persists, test the float switch. Locate the float switch in the secondary drain pan or inside the unit. Lift the float manually. You should hear an audible click and the multimeter should show continuity between the switch terminals. If the switch is seized or the float is stuck, replace the switch assembly.

If the float switch tests fine, the drain pump motor has failed. The pump impeller may be seized by debris. On some Fujitsu models, you can access the pump impeller through a side panel and clear the obstruction. If the motor is burned out, replace the pump.

3-Minute Restart Delay

Fujitsu mini splits include a 3-minute compressor restart delay. After the compressor stops for any reason (temperature satisfied, protection trip, power interruption), the indoor unit waits 3 minutes before allowing the compressor to restart. The indoor fan runs the whole time. This is not an error. Do not try to defeat this delay. It protects the compressor from slugging refrigerant.

LED Blink Patterns on the Indoor Unit

If the remote display is not available, read the diagnostic code from the LED indicators on the indoor unit. Fujitsu units use the Power LED (green) and Timer LED (orange) in combination:

Power LED blinking 1 per second: Communication fault (code 01)
Timer LED 2-blink pattern: Room sensor fault (code 04)
Timer LED 3-blink pattern: Coil sensor fault (code 05)
Both LEDs fast flashing: Check the outdoor unit (code 07 or code 15)
Power LED 1 blink + Timer LED 1 blink: Drain/float problem (code 11)

Count the blinks and watch for pauses to separate the digit. A 3-blink pause means one digit ends.

Parts Often Needed

Part	Location	Notes
Indoor room thermistor	Behind return air grille	10K NTC, OEM part number varies by model
Indoor coil thermistor	Clipped to evaporator	Same 10K NTC spec
Outdoor PCB fuse	On outdoor control board	6.3A or 10A blade type
Outdoor PCB	Outdoor electrical compartment	Match model number exactly
Drain pump	Inside indoor unit base	Inspect impeller first

Need Replacement Parts?

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When to Call a Professional

Code 07 (compressor fault) and code 10 (valve fault) require refrigerant handling certification and inverter diagnostic tools. Do not attempt compressor replacement yourself. If code 01 persists after you have verified wiring at both terminal blocks and replaced the outdoor PCB fuse, call a Fujitsu-authorized technician. The indoor-outdoor communication circuit uses proprietary signal levels that require manufacturer-specific test equipment.

Fujitsu Mini Split Diagnostic Error Codes — 2-Digit Code Guide

Need this fixed instead of diagnosed?

Price the common parts before you book service.

Run capacitor

Flame sensor

Igniter

Control board