Troubleshoot your Mitsubishi FR-F 500L inverter with our updated fault code guide. Learn to interpret “E.” error codes, access alarm history, and reset the drive to restore operation quickly.

FR-F 500L Fault Codes Reference Table

Below is the comprehensive list of fault codes for the Mitsubishi FR-F 500L series:

Mitsubishi FR-F 500L Fault Codes List

Fault Code and Meaning	Cause and Remedy
E.OC1 Overcurrent shut-off during acceleration	Cause: When the inverter output current reaches or exceeds approximately 150% of the rated current during acceleration, the protective circuit is activated to stop the inverter output. Check point: Check for sudden acceleration. Check for output short circuit. Remedy: Increase the acceleration time.
E.OC2 Overcurrent shut-off during constant speed	Cause: When the inverter output current reaches or exceeds approximately 150% of the rated current during constant speed, the protective circuit is activated to stop the inverter output. Check point: Check for sudden load change. Check for output short circuit. Remedy: Keep load stable.
E.OC3 Overcurrent shut-off during deceleration	Cause: When the inverter output current reaches or exceeds approximately 150% of the rated current during deceleration (other than acceleration or constant speed), the protective circuit is activated to stop the inverter output. Check point: Check for sudden speed reduction. Check for output short circuit. Check for too fast operation of motor's mechanical brake. Remedy: Increase the deceleration time. Adjust brake operation.
E.OV1 Regenerative overvoltage shut-off during acceleration	Cause: If regenerative energy causes the inverter's internal main circuit DC voltage to reach or exceed the specified value, the protective circuit is activated to stop the inverter output. It may also be activated by a surge voltage generated in the power supply system. Check point: Check for too slow acceleration. Remedy: Decrease the acceleration time.
E.OV2 Regenerative overvoltage shut-off during constant speed	Cause: If regenerative energy causes the inverter's internal main circuit DC voltage to reach or exceed the specified value during constant speed. Check point: Check for sudden load change. Remedy: Keep load stable. Use the brake unit or power return converter (FR-RC) as required.
E.OV3 Regenerative overvoltage shut-off during deceleration or stop	Cause: If regenerative energy causes the inverter's internal main circuit DC voltage to reach or exceed the specified value during deceleration or stop. Check point: Check for sudden speed reduction. Remedy: Increase the deceleration time. (Set the deceleration time which meets load GD²). Decrease the braking duty. Use the brake unit or power return converter (FR-RC) as required.
E.THM Motor overload shut-off (electronic overcurrent protection)	Cause: The electronic overcurrent protection detects motor overheat due to overload or reduced cooling capability during constant-speed operation. When 85% of value is reached, pre-alarm occurs. When specified value is reached, inverter stops. Check point: Check the motor for use under overload. Remedy: Reduce the load weight.
E.THT Inverter overload shut-off (electronic overcurrent protection)	Cause: If a current of more than 120% of the rated output current flows and overcurrent shut-off does not occur (150% or less), inverse-time characteristics cause the electronic overcurrent protection to be activated to stop the inverter output to protect output transistors. Check point: Check the motor for use under overload. Remedy: Reduce the load weight.
E.IPF Instantaneous power failure protection	Cause: If a power failure occurs for longer than 15ms. If power failure persists for longer than 100ms, the alarm warning output is not provided, and inverter restarts if start signal is on. Check point: Find the cause of instantaneous power failure occurrence. Remedy: Remedy the instantaneous power failure. Prepare a backup power supply for instantaneous power failure. Set the function of automatic restart after instantaneous power failure.
E.UVT Undervoltage protection	Cause: If the power supply voltage reduces below 150V (approx 300V for 400V class), output stops. Also activated if jumper is not connected across P-P1. Check point: Check for start of large-capacity motor. Check that a jumper or DC reactor is connected across terminals P-P1. Remedy: Check the power supply system equipment such as power supply. Connect a jumper or DC reactor across terminals P-P1.
E.FIN Fin overheat	Cause: If the cooling fin overheats, the overheat sensor is actuated to stop the inverter output. Check point: Check for too high ambient temperature. Check for cooling fin clogging. Remedy: Set the ambient temperature to within the specifications.
E.GF Output side ground fault overcurrent protection	Cause: This function stops the inverter output if a ground fault overcurrent flows due to a ground fault which occurred in the inverter's output (load) side at the start. Check point: Check for a ground fault in the motor and connection cable. Remedy: Remedy the ground fault portion.
E.OHT External thermal relay operation	Cause: If the external thermal relay designed for motor overheat protection or the internally mounted temperature relay in the motor switches on (contacts open). Check point: Check for motor overheating. Check that the value of 7 (OH signal) is set correctly in Pr. 180 to Pr. 186. Remedy: Reduce the load and operating duty.
E.OLT Stall prevention (Stll Prev STP) The running frequency has fallen to 0 by stall prevention activated.	Cause: Check the motor for use under overload. Remedy: Reduce the load weight.
E.OPT Option alarm (Option Fault) Stops the inverter output if the dedicated option used results in setting error or connection fault.	Cause: AC power supply is connected to R, S, T <L1, L2, L3> when high power factor converter connection is selected. Remedy: Check option connection and power supply settings.
E.OP1 to E.OP3 Option slot alarm 1 to 3 Stops the inverter output if a functional alarm occurs in the plug-in option loaded in the corresponding slot.	Cause: Check for a wrong option function setting and operation (1 to 3 indicate option slot numbers). Remedy: Confirm the option function setting, etc.
E.PE Parameter storage device alarm (Corrupt Memory) Stops the inverter output if a fault occurs in the E²PROM device.	Cause: Check for too many number of parameter write times. Remedy: Change the inverter.
E.PUE Parameter unit disconnection (PU Leave Out) Communication between the inverter and PU is suspended/disconnected.	Cause: Check for loose fitting of the DU or PU. Check the Pr. 75 setting. Remedy: Fit the DU and PU securely.
E.RET Retry count exceeded (Retry No Over) If operation cannot be resumed properly within the number of retries set.	Cause: Find the cause of alarm occurrence. Remedy: Eliminate the cause of the error preceding this error indication.
E.LF Output phase failure protection Stops output if one of the three phases (U, V, W) on the load side results in open phase.	Cause: Check the wiring (Check the motor for a fault). Remedy: Wire the cables properly.
E.CPU CPU Error (CPU Fault) Arithmetic operation of built-in CPU does not end within predetermined period.	Cause: Internal calculation error or connection issue. Remedy: Make connection securely.
E.6 CPU Error (Error 6) Arithmetic operation of peripheral circuit of built-in CPU does not end within predetermined period.	Cause: Check for a loose connector. Remedy: Make connection securely.
E.7 CPU Error (Error 7) Arithmetic operation of peripheral circuit of built-in CPU does not end within predetermined period.	Cause: Internal circuit timeout. Remedy: Make connection securely.
E.LF (Duplicate) Error (Built-in CPU Malfunction) The inverter output is stopped if a malfunction occurs in the built-in CPU.	Cause: Check value of parameter, operation mode and connectors. Remedy: Make connection securely.
E.P24 24VDC power output short circuit 24VDC power output from the PC terminal is shorted.	Cause: Check for a short circuit in the PC terminal output. Remedy: Remedy the short circuit portion. (Reset via operation panel or power cycle).
E.CTE Operation panel power supply short circuit Operation panel power supply (P5S of the PU connector) is shorted.	Cause: Check for a short circuit in the PU connector cable. Remedy: Check the PU and cable. (Reset via RES signal or power cycle).
E.15 Main circuit error (Error 15) Brake unit overheat, DC fuse blown, control board temp error, output overcurrent, etc.	Cause: Multiple hardware causes (Cooling fin, DC fuse, Gate power supply). Refer to manual page 148. Remedy: Refer to detailed manual investigation procedures.

 

How to Read FR-F 500L Faults via Operation Panel & Software

To get the most accurate diagnostic data in 2026, you can utilize the local Parameter Unit (PU) or connect via PC using Mitsubishi setup software (FR-Configurator).

1. Alarm History (Parameter Unit)

The FR-F 500L stores the most recent fault history. By navigating to the Alarm History Mode on the operation panel, you can view the last 8 alarms. This is crucial for identifying recurring issues that happen when you aren’t watching the drive.

2. Diagnostic Display

When the drive trips, the display alternates between the error code (e.g., E.OC1) and the output frequency at the time of the trip. Pressing the “SET” key during a fault often reveals the output voltage and current at the moment of failure.

3. FR-Configurator / Setup Software

For advanced troubleshooting, connecting a PC allows you to use the Graph Function (oscilloscope function). This records waveform data (current, voltage, speed) leading up to the trip, helping you distinguish between load issues and drive hardware failures.

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Frequently Asked Questions (FAQ)

Q: What is the difference between a Minor Fault and a Major Fault?

A: The Mitsubishi system categorizes these as:

• Minor Fault (Warning): The display may blink or show a specific code (like ‘OL’ for Overload or ‘PS’ for PU Stop), but the drive may continue to operate or decelerate safely.
• Major Fault (Protective Function): Codes starting with “E.” (e.g., E.OV1, E.THM). These immediately shut off the inverter output to prevent damage to the IGBTs or motor.

Q: How do I reset a Mitsubishi FR-F 500L fault?

A: You can reset the inverter using one of the following methods:

• Press the STOP/RESET button on the operation panel.
• Turn the power supply OFF and then ON again (Power Cycle).
• Short the RES (Reset) terminal to the SD (Common) terminal for more than 0.1 seconds via an external switch.

Q: Why does my drive show E.OC1 (Overcurrent)?

A: E.OC1 is one of the most common faults. It usually indicates a short circuit in the motor wiring, a locked rotor, or acceleration that is set too fast for the load inertia.