Troubleshoot your Mitsubishi FR-S500 micro-drive using our fault code guide. Learn to use the Digital Dial for diagnostics, interpret E.OC1/E.OV1 errors, and clear alarm history.

FR-S500 Fault Codes Reference Table

Below is the complete list of fault codes and error messages for the S500 series. Please use the search function to find your specific code.

Mitsubishi FR-S500 Fault Codes List

Fault Code and Meaning	Cause and Remedy
OC1 (FR-PU04: OC During Acc) Overcurrent cut-off during acceleration	Cause: When the inverter output current reaches or exceeds approximately 200% of the rated inverter current during acceleration, the protective circuit is activated to stop the inverter output. Check points: Check for sudden acceleration. Check for output short-circuit/ground fault. Remedy: Increase the acceleration time.
OC2 (FR-PU04: Stedy Spd OC) Overcurrent cut-off during constant speed	Cause: When the inverter output current reaches or exceeds approximately 200% of the rated inverter current during constant-speed operation, the protective circuit is activated to stop the inverter output. Check points: Check for sudden load change. Check for output short-circuit/ground fault. Remedy: Keep load stable.
OC3 (FR-PU04: OC During Dec) Overcurrent cut-off during deceleration	Cause: When the inverter output current reaches or exceeds approximately 200% of the rated inverter current during deceleration (other than acceleration or constant speed), the protective circuit is activated to stop the inverter output. Check points: Check for sudden speed reduction. Check for output short-circuit/ground fault. Check for too fast operation of motor's mechanical brake. Remedy: Increase the deceleration time. Adjust brake operation.
OV1 (FR-PU04: OV During Acc) Regenerative overvoltage cut-off during acceleration	Cause: When the main circuit DC voltage in the inverter rises to or above the specified value due to excessive regenerative energy during acceleration. May also be activated by surge voltage in power supply. Check points: Check for too slow acceleration. Remedy: Decrease the acceleration time. Install a power factor improving reactor.
OV2 (FR-PU04: Stedy Spd OV) Regenerative overvoltage cut-off during constant speed	Cause: When the main circuit DC voltage in the inverter rises to or above the specified value due to excessive regenerative energy during constant speed. May also be activated by surge voltage in power supply. Check points: Check for sudden load change. Remedy: Keep load stable. Install a power factor improving reactor.
OV3 (FR-PU04: OV During Dec) Regenerative overvoltage cut-off during deceleration or stop	Cause: When the main circuit DC voltage in the inverter rises to or above the specified value due to excessive regenerative energy during deceleration or stop. May also be activated by surge voltage in power supply. Check points: Check for sudden speed reduction. Remedy: Increase the deceleration time. (Set the deceleration time which matches the inertia moment of the load). Decrease the braking duty. Install a power factor improving reactor.
THM (FR-PU04: Motor Overload) Motor overload cut-off (electronic thermal overcurrent protection)	Cause: The electronic overcurrent protection detects motor overheat due to overload or reduced cooling capability during low-speed operation. Check points: Check the motor for use under overload. Remedy: Reduce the load weight. For the constant-torque motor, change the Pr. 71 setting to the constant-torque motor setting.
THT (FR-PU04: Inv. Overload) Inverter overload cut-off (electronic thermal overcurrent protection)	Cause: If a current of more than 150% of the rated output current flows and overcurrent shut-off does not occur (200% or less), inverse-time characteristics activate protection to stop the inverter output to protect output transistors. Check points: Check the motor for use under overload. Remedy: Reduce the load weight.
FIN (FR-PU04: H/Sink O/Temp) Fin overheat	Cause: If the cooling fin overheats, the overheat sensor is actuated to stop the inverter output. Check points: Check for too high ambient temperature. Check for cooling fin clogging. Remedy: Set the ambient temperature to within the specifications. Clean the cooling fins.
GF (FR-PU04: Ground Fault) Start-time output side ground fault overcurrent protection	Cause: A ground fault overcurrent flowed due to a ground fault which occurred in the inverter's output (load) side. (Valid when Pr. 40 = "1"). Check points: Check for a ground fault in the motor and connection cable. Remedy: Remedy the ground fault portion.
OHT (FR-PU04: OH Fault) External thermal relay	Cause: The external thermal relay (motor overheat protection) or internally mounted temperature relay in the motor switched on (contacts open). Check points: Check for motor overheating. Check that value of 7 (OH signal) is set correctly in Pr. 60 to Pr. 63. Remedy: Reduce the load and operating duty.
OLT (FR-PU04: Stll Prev STP) Stall prevention (overload)	Cause: The running frequency has fallen to 0 by stall prevention operation activated. OL appears while stall prevention is being activated. Check points: Check the motor for use under overload. Remedy: Reduce the load weight.
OPT (FR-PU04: Option Fault) Communication error	Cause: A setting error or connection (connector) fault occurred during use of the RS-485 communication function. Check points: Check that the connector is plugged securely. Remedy: Make connection securely. Please contact your sales representative.
PE (FR-PU04: Corrupt Memory) Parameter error	Cause: A fault occurred in parameters stored (example: E2PROM fault). Check points: Check for too many number of parameter write times. Remedy: Please contact your sales representative.
PUE PU disconnected	Cause: Communication between inverter and PU is suspended (e.g., if the PU is disconnected with "1" set in parameter n17). Remedy: Fit the FR-PU04 securely.
RET Retry count	Cause: If operation cannot be resumed properly within the number of retries set, this function stops the inverter output. Remedy: Eliminate the cause of the error preceding this error indication.
CPU CPU error	Cause: If the arithmetic operation of the built-in CPU does not end within a predetermined period, the inverter self-determines it as an alarm. Remedy: Please contact your sales representative.
FN Fan trouble	Cause: The cooling fan stops due to a fault or operates differently from the setting of Pr. 76 "cooling fan operation selection". Remedy: Change the fan.
OL Stall prevention (overcurrent)	Cause: Current of more than 150% of the rated inverter current flows in the motor during acceleration, constant speed, or deceleration. The function stops frequency change to prevent overcurrent shut-off. Remedy: The acceleration/deceleration time may change. Increase the stall prevention operation level with Pr. 22. Disable stall prevention with Pr. 21. Check that the torque boost (Pr. 0) setting is not higher than required.
oL Stall prevention (overvoltage)	Cause: During deceleration, if regenerative energy increases too much to exceed brake capability, this function stops the decrease in frequency to prevent overvoltage shut-off. Remedy: Increase the deceleration time using Pr. 8 "deceleration time".
PS PU stop (Stopped with PU STOP key)	Cause: Pr. 75 "reset selection/PU stop selection" had been set and a stop was made by pressing the STOP/RESET key during external operation mode. Remedy: Refer to page 94 (Check for a stop made by pressing the STOP/RESET key).
UV Undervoltage	Cause: Power supply voltage reduced below about 115VAC (230VAC for 400V series) resulting in control circuit issues. Remedy: Check the power supply system equipment. Check for a start of large-capacity motor.
Er1 Write disable error	Cause: Write performed with "1" (write disable) set in Pr. 77. Frequency jump setting range overlapped. Parameter write performed without write precedence (only for RS-485 types). Remedy: Check the setting of Pr. 77 "parameter write disable selection". Check the settings of Pr. 31 to 36 (frequency jump). Check communication operation settings.
Er2 Write-while-running / mode designation error	Cause: Write was performed during operation. Attempt made to change Pr. 79 setting while operation command input. Write performed in external operation mode. Remedy: After stopping operation, make parameter setting. After setting the operation mode to "PU operation mode", make parameter setting.
Er3 Calibration error	Cause: Analog input bias and gain calibration values are too close. Remedy: Check the settings of C3, C4, C6, and C7 (calibration functions).

 

How to Read FR-S500 Faults via the Digital Dial

The FR-S500 is unique because it relies on a central Digital Setting Dial for both operation and diagnostics. Here is how to use the built-in interface to troubleshoot issues effectively:

• Active Fault Display: When the drive trips, the display automatically switches to the Alarm Indication mode. It will alternate between the fault code (e.g., E.THT) and the output frequency at the time of the trip (e.g., 0.0).
• Accessing Alarm History: The S500 memory retains the last 4 alarms. To retrieve them:
  1. Press the MODE button until the display shows the parameter setting mode.
  2. Turn the Digital Dial to locate the alarm history parameters (often automated in the monitoring loop).
  3. The most recent alarm is displayed first. Turning the dial further will show older alarms (indicated as dot suffixes like E.OC1.).
• Using External Keypads: If the onboard display is difficult to access, the FR-S500 is compatible with the FR-PU04 or FR-PU07 parameter units (connected via cable), which display full text descriptions of the faults rather than just codes.

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Frequently Asked Questions (FAQ)

Q: What does a flashing “OL” mean on the FR-S500?
A: OL stands for Overload (Stall Prevention). This is a Warning, not a Fault. It means the motor is drawing too much current, and the drive is actively lowering the frequency to prevent a full trip. If the load isn’t reduced, it will eventually trip on E.THM (Thermal Overload).

Q: How do I reset the FR-S500 after a fault?
A: You can reset the drive using one of the following methods:

• Press the STOP/RESET button on the front panel.
• Cycle the main power (Wait for the LED display to fully extinguish before turning power back on).
• Connect the RES (Reset) terminal to the SD (Common) terminal for at least 0.1 seconds.

Q: Can I clear the fault history?
A: Yes. You can clear the stored alarm history by performing an “All Clear” or “Parameter Clear” operation using the parameter settings, usually found under parameter Pr.CL (Parameter Clear) in the setup menu.