Engineering guide
Toshiba G9000 fault codes explained
On a Toshiba G9000, codes starting with UA are alarms and codes starting with UF are failures, according to section 8 of Toshiba's installation and operation manual 61480-018. The last two digits tell you the weight: 00 to 49 is a Major failure, where the load goes to the static bypass line, and 50 to 99 is a Minor one, where the UPS keeps running but the cause still has to be found. The tables below give the manual's meaning and guidance for the codes operators meet most.
Key facts
- UA808 INVERTER OVERLOAD: load current above 150% of rated current
- UA codes: alarms; UF codes are failures
- Last two digits 00 to 49: Major failure; 50 to 99 is Minor
- UA805 INVERTER OVERLOAD: load current above 105% of rated current
How a G9000 code is built
The second letter separates alarms (UA) from failures (UF). The first digit after the letters points to the circuit: 0 for the rectifier, 1 for the DC circuit, 2 for the inverter, 3 for control, 4 for the bypass system and 8 for alarms. The last two digits give the weight: 00 to 49 is Major, 50 to 99 is Minor.
The display shows the code, a status message and a guidance line. Note all three, with the time, before anyone resets the unit; the manual asks for that record first.
Input and bypass alarms
| Code | Message on the display | What the manual says | What to do |
|---|---|---|---|
| UA801 | AC INPUT VOLTAGE OUT OF RANGE | Input line voltage out of the specified range. | Check the input power source. |
| UA802 | AC INPUT FREQUENCY OUT OF RANGE | Input line frequency out of the specified range. | Check the input power source; a generator may be running. |
| UA803 | AC INPUT PHASE ROTATION ERROR | Input conductors not in the proper phase sequence. | Have an electrician check the input wiring. |
| UA812 | BYPASS VOLTAGE OUT OF RANGE | Bypass line voltage out of the specified range. | Check the bypass input. |
| UA813 | BYPASS PHASE ROTATION ERROR | Bypass conductors not in the proper phase sequence. | Have an electrician check the bypass wiring. |
| UA814 | BYPASS FREQUENCY OUT OF RANGE | Bypass line frequency out of the specified range. | Check the bypass input. |
| UA815 | TRANSFER PROHIBITED | Transfer to bypass unavailable because the bypass is abnormal. | Postpone any planned transfer. |
| UA835 | TRANSFER PROHIBITED | The UPS could not transfer because the bypass source has an abnormality. | Check the bypass source. |
These alarms report the supply. Check for a utility event, a generator start or recent upstream work. A phase rotation error after electrical work is corrected at the wiring, by an electrician.
Overload alarms
| Code | Message on the display | What the manual says | What to do |
|---|---|---|---|
| UA805 | INVERTER OVERLOAD | Output load current above 105% of rated current. | Reduce the load (DECREASE LOAD). |
| UA806 | INVERTER OVERLOAD | Output load current above 110% of rated current. | Reduce the load. |
| UA807 | INVERTER OVERLOAD | Output load current above 125% of rated current. | Reduce the load. |
| UA808 | INVERTER OVERLOAD | Output load current above 150% of rated current. | Reduce the load now. |
| UA810 | INVERTER OVERLOAD | Short-time overcurrent detected during inverter operation. | Reduce the load. |
| UA870 | BALANCER OVERLOAD | Neutral point voltage unbalance detected. | Check how single-phase loads are spread across phases. |
| UF258 | LOAD ABNORMAL | Load transferred for overload more than 4 times within 5 minutes. | Call a technician. |
The four inverter overload codes step up from 105% to 150% of rated current, so the code itself tells you how far over the unit is. Shed non-critical load first. UF258 means four transfers in five minutes: leave the load on bypass and call.
Battery codes
| Code | Message on the display | What the manual says | What to do |
|---|---|---|---|
| UA824 | CB2 OPEN | The battery circuit breaker (CB2) is open. | Confirm whether it was opened for work; the guidance is TURN ON CB2. |
| UA834 | BATTERY DEPLETED/AC OUT STOPPED | Battery voltage has reached the depleted level (Major). | Restore the input supply; call a technician. |
| UF157 | BATTERY OVERTEMPERATURE | Overtemperature detected at the batteries. | Check the battery room temperature (CHECK BATTERY). |
| UF158 | BATTERY LIQUID LOW | Low battery electrolyte level. | Have the battery string inspected (CHECK BATTERY). |
| UF162 | BATTERY ABNORMAL | Failure found by the battery self-check. | Call a technician. |
| UF163 | BATTERY VOLTAGE ABNORMAL | Battery voltage is abnormal. | Call a technician. |
Overtemperature and self-check failures are usually the first sign that a string is aging. Our Toshiba UPS service team tests the string under load before deciding on replacement, and matching blocks for G9000 cabinets are in the replacement battery catalogue.
Breakers, emergency stop and external signals
| Code | Message on the display | What the manual says | What to do |
|---|---|---|---|
| UA817 | EMERGENCY STOP ACTIVATED | Emergency stop activated by the EPO switch or an external contact. | Find what triggered the EPO before any restart. |
| UA822 | TRANSFER PROHIBITED | No transfer to bypass because the generator-operation signal says a backup generator is running. | Expected while on generator. |
| UA831 | EMERGENCY BYPASS SWITCH ON | The emergency bypass switch has been turned on. | Check whether work is under way; call a technician. |
| UA833 | 52L OPEN | The load circuit breaker (52L) is turned off. | Confirm whether it was opened on purpose. |
| UA890 | EXTERNAL ALARM | An external alarm relay turned on. | Check the equipment wired to that input. |
| UF420 | 52L OPERATION ERROR | Load breaker 52L opened during inverter operation (Major). | Call a technician (guidance: CHECK 52L). |
Failures that need a technician
| Code | Message on the display | What the manual says | What to do |
|---|---|---|---|
| UF102 | DC OVERVOLTAGE | DC voltage above the overvoltage level (Major). | Call a technician. |
| UF103 | DC UNDERVOLTAGE | DC voltage below the undervoltage level (Major). | Call a technician. |
| UF201 | INVERTER OVERVOLTAGE | Output overvoltage detected (Major). | Call a technician. |
| UF203 | INVERTER OVERCURRENT | Inverter overcurrent detected (Major). | Call a technician. |
| UF213 | OVERTEMP | Heatsink temperature above its thermal setting (Major). | Call a technician; check the room cooling. |
| UF214 | COOLING FAN ABNORMAL | Thermal relay protection activated (Major). | Call a technician. |
| UF301 | UPS CONTROL CIRCUIT ERROR | AD reference has an abnormal value (Major). | Call a technician. |
| UF401 | 52S ABNORMAL | Contactor 52S failed to close (Major). | Call a technician. |
Every UF code with CALL SERVICE ENGINEER is a technician job. Keep the cabinet closed, leave the load where the UPS put it, and pass on the record of codes and times.
Related pages
Common questions
What is the difference between UA and UF on a Toshiba G9000?
UA codes are alarms and UF codes are failures, per the code key in manual 61480-018.
How do I know if a G9000 failure is Major?
Look at the last two digits: 00 to 49 is Major, with the load moved to the static bypass; 50 to 99 is Minor.
What does UA805 INVERTER OVERLOAD mean?
The output load current has exceeded 105% of the rated current. Reduce the load.
Why does the G9000 refuse to transfer to bypass on generator?
UA822 appears when the generator-operation signal says a backup generator is running; the transfer is blocked on purpose.
What does UF213 OVERTEMP mean?
The heatsink temperature exceeded its thermal setting. It is a Major failure: call a technician and check the room cooling.
Sources, checked October 4, 2026:
- Toshiba G9000 Series Installation and Operation Manual 480/480 V 300-750 kVA, Document 61480-018, Rev. J (January 2022), section 8, p. 73
- Toshiba G9000 Series Installation and Operation Manual 480/480 V 300-750 kVA, Document 61480-018, Rev. J (January 2022), Table 8-1 notes, p. 77
- Toshiba G9000 Series Installation and Operation Manual 480/480 V 300-750 kVA, Document 61480-018, Rev. J (January 2022), Table 8-1, pp. 73-74, 73-76, 74-75, 74-77
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