Toshiba Q9 Fault Codes List

Troubleshoot your Toshiba Q9 HVAC drive with our updated fault code guide. Learn to interpret OC, OL, and EPH trips, view the LCD trip history, and reset faults.

Toshiba Q9 Fault Codes Reference Table

Below is the complete list of trip codes and alarms. Please refer to this table to match the code on your LCD display with the specific hardware or parameter issue.

Toshiba Q9 ASD - User Notification Codes, Alarms, and Faults

Fault Code and Meaning	Cause and Remedy
Atn Autotune active.	Cause: Autotune function is currently running. Remedy: Indication only; no action required.
ETN Autotuning error.	Cause: Autotune readings significantly inconsistent with configuration. A non-3-phase motor is being used. Improper settings at F400 or F410 to F413. Motor rating significantly smaller than ASD rating. Output cabling too small, too long, or EMF interference. Motor is running during Autotune. Remedy: Verify motor wiring and type. Check and adjust parameters F400 and F410-F413. Ensure motor is stopped before tuning.
ETN1 Autotuning error — Torque boost error.	Cause: Improper setting at F410. Remedy: Correct setting F410.
ETN2 Autotuning error — Leak inductance error.	Cause: Improper setting at F412. Remedy: Correct setting F412.
ETN3 Autotuning error — Motor rating error.	Cause: Improper setting at F405, F406, or F407. Remedy: Correct settings F405, F406, or F407.
ETYP Typeform error.	Cause: Firmware information inconsistent between Application Board and Motor Control board. Application Board or Motor Control board is defective. Remedy: Perform a Typeform Reset. Replace defective board if reset fails.
4-20 mA 4-20 Signal Loss.	Cause: Misconnection, poor connection, or broken wire. Improper programming at F201 and associated parameters. Remedy: Check wiring continuity. Verify parameter F201.
CM1 Internal communications error.	Cause: Improperly programmed ASD. Improper communications settings. Remedy: Check communications programming.
CM2 External communications error.	Cause: Improperly connected cables. Remedy: Secure and check external cable connections.
COFF Under-voltage condition at optional Control power supply.	Cause: Misconnection, poor connection, or broken wire. Defective power supply. Remedy: Check wiring. Replace power supply if defective.
DAMP Damper closed.	Cause: Improper configuration/programming for Damper Control at discrete input terminals. Remedy: Check discrete input terminal configuration.
Emergency Off Output signal terminated/Brake applied.	Cause: Stop-Reset pressed twice at the EOI. EOFF command received remotely. Remedy: ASD reset required.
HLD Heavy load — motor/ASD overloaded.	Cause: Accel setting is too short. ASD/Motor not right-sized for application. Excessively fluctuating load. Remedy: Increase Accel time. Verify motor/drive sizing.
LLD Light load.	Cause: ASD/Motor should be right-sized for application. Remedy: Verify load matches drive capacity.
LLT Lower-limit time.	Cause: Parameter F256 adjustment required. Remedy: Adjust parameter F256.
LTA Part replacement alarm.	Cause: Part Replacement Alarm activation as set at F634. Remedy: Perform scheduled maintenance/replacement.
MOFF Main under-voltage condition.	Cause: Low 3-phase commercial power voltage level. Remedy: Check input power supply voltage.
OC Over-Current — ASD output > F601.	Cause: Phase-to-phase short (U, V, or W). Defective IGBT. Output cabling connected incorrectly. Restarting into a spinning motor (no catch-spin). Motor/machine jammed or brake engaged. Accel/Decel too short or Voltage Boost too high. Load fluctuations or high temp. Remedy: Check cabling and motor for shorts. Check for mechanical jams. Adjust Accel/Decel or V/f settings.
OH Overheat — ASD ambient temp excessive.	Cause: ASD operating at elevated temperature. Cooling fan obstructed or inoperative. Internal thermistor disconnected. Remedy: Clean vents and check fans. Reduce ambient temperature.
OJ User-set run-time counter exceeded.	Cause: Run-timer limit reached. Remedy: Type Reset required; select Clear run timer.
OLI ASD overload.	Cause: Carrier frequency too high. Excessive load. Accel time too short. DC damping rate too high. Motor starting into spinning load. Remedy: Reduce carrier frequency. Increase Accel time. Check load conditions.
OLM Motor overload.	Cause: V/f parameter improperly set. Motor locked or running low speed continuously. Motor improperly matched to load. Remedy: Adjust V/f parameters. Check for motor locking/jams.
OLST Overload soft Stall active.	Cause: Soft Stall Selection adjustment required (F017). Remedy: Adjust parameter F017.
OP DC bus voltage exceeds specifications.	Cause: Starting into spinning motor after momentary power loss. High input voltage or spikes (install inductive filter). Decel time too short. Regenerative load (Over-voltage stall turned off). Remedy: Increase Decel time. Install input reactor/filter. Enable Ridethrough (F302) or Over-voltage stall.
OT Over-torque.	Cause: Torque requirement exceeds F616/F617 for time > F618. ASD not matched to application. Load obstructed. Remedy: Check load for obstructions. Adjust torque parameters F616, F617, F618.
POFF Under-voltage at 5, 15, or 24 VDC supply.	Cause: Defective Control board. Excessive load on power supply. Low input voltage. Remedy: Check input voltage. Replace Control board if defective.
POT Pre-over-torque.	Cause: Torque requirement exceeds F616 or F617. Load obstructed. Remedy: Clear load obstruction. Adjust F616/F617 if necessary.
PTC Optional thermal sensor threshold exceeded.	Cause: User-set thermal threshold (F646) exceeded. Remedy: Check temperature or adjust F646.
UC Under-current.	Cause: Current below level defined at F611. Remedy: Disable detection at F610 or adjust F611.
E-10 Over-voltage at analog input.	Cause: Mis-wire at the ASD input terminals. Remedy: Check input terminal wiring.
E-12 Open circuit at shaft-mounted encoder.	Cause: Encoder signal missing. Remedy: Check encoder connection.
E-13 Over-speed error.	Cause: Motor speed > commanded speed. Improper encoder connection or setup. Defective encoder. Remedy: Check encoder setup and hardware.
E-18 Loss of signal at analog input.	Cause: V/I input missing or low. Over-current at P24. Remedy: Check analog signal source.
E-19 CPU communication error.	Cause: Internal CPU communication failure. Remedy: Service call required.
E-20 Speed/torque/direction signal error.	Cause: Control signal transfer error. Remedy: Service call required.
E-21 Stack overflow error.	Cause: Internal processing error. Remedy: Service call required.
E-22 Improper input voltage at discrete input.	Cause: Input activation voltage out of specification. Remedy: Check discrete input voltage levels.
E-23 Expansion card option 1 hardware error.	Cause: Option card 1 failure. Remedy: Service call required.
E-24 Expansion card option 2 hardware error.	Cause: Option card 2 failure. Remedy: Service call required.
E-26 CPU fault.	Cause: Internal CPU fault. Remedy: Service call required.
EEP1 EEPROM write error.	Cause: Data storage failure. Remedy: Service call required.
EEP2 / EEP3 EEPROM read error.	Cause: Data retrieval failure during initialization. Remedy: Service call required.
EF1 Software-detected earth fault.	Cause: Mis-wired ground. Loose ground connection. ASD setup improperly. Remedy: Verify ground wiring.
EF2 Hardware-detected earth fault.	Cause: Mis-wired ground or loose connection. Remedy: Verify ground wiring.
Emergency Off Emergency Off command (Trip).	Cause: Stop-Reset pressed twice. EOFF command received. Remedy: ASD reset required. Check stopping method at F603.
EPHI Input phase loss (R, S, or T).	Cause: Mis-wired input phase. Loose input phase connection. Remedy: Check input power wiring.
EPHO Output phase loss (U, V, or W).	Cause: Mis-wired output phase. Loose output phase connection. Remedy: Check motor wiring.
ERR2 / ERR3 / ERR4 / ERR5 / ERR6 Internal ROM/RAM/CPU/Comm/Gate Array errors.	Cause: Internal hardware or communication timeouts. Improper setup or connections (ERR5/ERR8). Remedy: Service call required (for most hardware errors). Check cables and setup (for Comm/Net errors).
OC1 / OC1P Over-current during acceleration.	Cause: V/f setting needs adjustment. Restart from momentary power outage. Starting into rotating motor. Phase-to-phase short. Accel time too short. Voltage Boost too high. Motor jammed or brake engaged. Remedy: Adjust V/f or Accel settings. Clear jams/brakes. Check for shorts.
OC2 / OC2P Over-current during deceleration.	Cause: Phase-to-phase short. Decel time too short. Motor/machine jammed. Remedy: Increase Decel time. Check for shorts/jams.
OC3 / OC3P Over-current during run.	Cause: ASD/Motor load not matched. Load fluctuations. Elevated temperature. Remedy: Verify drive sizing. Check cooling.
OCA1 / OCA2 / OCA3 Over-current at U/V/W phase IGBT.	Cause: Low impedance at the specific phase (U, V, or W). Remedy: Check IGBT and motor phase impedance.
OCL Output short circuit at U-V-W.	Cause: Phase-to-phase short. Starting into rotating motor. Short Circuit Detection adjustment required (F613). Remedy: Check wiring for shorts. Adjust F613.
OH Over temperature error.	Cause: Cooling fan inoperative. Ventilation obstructed. Remedy: Check fans and clear vents.
OH2 Over temperature at PTC1/PTC2.	Cause: Over-temperature detected by option board. See F637 and F638. Remedy: Check external device temperature.
OL1 ASD overload error.	Cause: Accel time too short. DC Injection current too high. V/f setting needs adjustment. Remedy: Adjust Accel or V/f settings.
OL2 Motor overload error.	Cause: Motor locked or continuous low speed. Load exceeds motor ability. Remedy: Check for jams. Review sizing.
OP1 / OP2 / OP3 Over-voltage (Accel/Decel/Run).	Cause: Motor running during restart. Decel time too short. Stall protection disabled. Input voltage out of spec. Remedy: Increase Decel time. Check input voltage. Install input reactance if needed.
OT Over-torque error.	Cause: Torque exceeds F616/F617 settings. Load obstructed. Remedy: Clear obstruction. Adjust torque parameters.
SOUT Permanent magnet motor pull out trip.	Cause: Motor sync loss. Remedy: Service call required.
UC Low-Current error.	Cause: Improper low-current detection level setting. Remedy: Adjust detection level.
UP1 Main power under-voltage.	Cause: 3-phase input voltage low. Defective control board. Excessive load on power supply. Under-Voltage/Ridethrough settings require adjustment. Remedy: Check input power. Adjust Ridethrough settings.

 

How to Read Q9 Faults via LCD Keypad (EOI)

The Q9’s Electronic Operator Interface (EOI) is a powerful tool for facility managers. In 2026, you can access deep diagnostic data directly from the keypad without needing a laptop or proprietary software:

• Trip History: The Q9 records the last 4 faults in its non-volatile memory. Press the MON (Monitor) button and scroll down to “Trip History.” This shows the chronological order of failures (Past Trip 1 through 4).
• Status at Trip: By selecting a specific past trip and pressing ENT (Enter), you can view the “At-Trip” data. This captures the output frequency, current, and voltage at the exact moment the drive tripped—vital for knowing if a pump was ramping up or running steady.
• I/O Status: You can view the real-time status of input terminals (RES, S1, S2, etc.) to verify if an external safety interlock, such as a Freeze Stat or Vibration Switch, triggered the shutdown.

General Troubleshooting Steps

Before resetting an HVAC drive, ensure you check the mechanical systems to prevent damage:

1. Overcurrent (OC1/OC2/OC3): Short circuit or ground fault. In HVAC applications, check for water intrusion in the motor peckerhead or conduit. Perform a megger test if the fault persists.
2. Overload (OL1/OL2): OL1 is Motor Overload; OL2 is Drive Overload. Check for slipping belts causing torque spikes, closed dampers preventing airflow (backpressure), or seized bearings on the fan shaft.
3. Input Phase Failure (EPH1): This indicates a loss of one of the incoming power phases. Check your building’s fuses or disconnect switches immediately, as running on single-phase can destroy the drive’s input rectifier.

Frequently Asked Questions (FAQ)

Q: What is the difference between an Alarm (C code) and a Fault?

A: An Alarm (flashing codes starting with “C”, like CM00) alerts you to a condition—such as high current—but allows the fan or pump to continue running. A Fault (codes like OC or E) instantly stops the output to protect the equipment.

Q: How do I reset a Toshiba Q9 fault?

A: You can reset the drive using one of these methods:

• Press the STOP/RESET key on the keypad twice.
• Momentarily close the RES (Reset) terminal to CC (Common).
• Cycle the main power (Turn OFF, wait for the screen to go black, Turn ON).

Q: Why does the drive display “OFF”?

A: OFF means the drive is powered and ready but has no “Run” command. In HVAC, this often means the Building Automation System (BAS) is not calling for the unit to run, or the “Hand/Off/Auto” switch is in the Off position.