APC Smart-UPS Fault Codes and Alarms Explained | Indigi Power & Cooling
Common APC Smart-UPS Fault Codes and Alarms Explained
The APC Smart-UPS is the world's most widely deployed UPS platform for server rooms, IT racks, and network infrastructure - and the most commonly Googled UPS when something goes wrong. Whether your unit is beeping, showing a red LED, displaying a cryptic code on the LCD, or sitting stuck in bypass mode, this guide will tell you exactly what is happening and what to do about it.
This guide covers the SMT (Smart-UPS SMT), SMX (Smart-UPS X), and SRT (Smart-UPS SRT Online) ranges, which share common alarm behaviour across the APC Smart-UPS family.
Reading the APC Smart-UPS Front Panel
LCD Status Indicators
The Smart-UPS LCD display shows a combination of icons and text messages. The key status icons to understand:
Beep Patterns
APC Smart-UPS Fault Code Reference Table
The Smart-UPS SMT, SMX, and SRT display alphanumeric fault codes on the LCD alongside the alarm text. Use this table to identify exactly what your unit is telling you.
P. Codes - Output and Power Faults
b. Codes - Battery Faults
G. Codes - Site and General Faults
Alarm Text Messages (LCD Display - No Code)
How to retrieve fault history on your APC Smart-UPS:
The Smart-UPS maintains an internal error log accessible from the front panel:
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Press any button to activate the display
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Navigate to Logs > Error Log on the LCD menu
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Review all stored events and faults with timestamps
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To clear the log after resolving a fault, navigate to Logs > Reset Energy Meter
Fault 1: Replace Battery
What it looks like: Replace Battery LED illuminated amber or red. UPS emits short beeps for one minute, then repeats the alarm every five hours.
What it means: The UPS has detected that the battery either failed a self-test, has a weak charge, or has reached the end of its design life. The connected load is still powered and protected but runtime is reduced and unreliable.
What to check first:
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Check when the battery was last replaced. APC VRLA batteries in the Smart-UPS range last 2-4 years depending on ambient temperature and discharge history. In Australian conditions, expect the shorter end of that range.
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Navigate to Configuration > UPS Self Test and run a manual self-test. If the unit passes, allow the battery to charge fully for 24 hours and retest. If it fails again, replacement is required.
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Check if the LCD shows "LifeTime NearEnd" or "LifeTime Exceeded" - this is the battery management system calculating based on accumulated charge cycles and time that the battery has reached end of service life.
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Check for the "Battery Disconnected" variant (beeping every 2 seconds) - if the battery connector is not fully engaged, reseating it may clear the fault immediately.
Resolution: Genuine APC replacement battery cartridges (RBCs) are available for every Smart-UPS model. The RBC number for your specific unit is printed on a label inside the battery access door. Do not use third-party batteries - they can cause continued Replace Battery alarms and may void warranty. For a full guide on battery replacement timing, see our article on how often UPS batteries should be replaced.
Fault 2: Internal UPS Fault (System Error)
What it looks like: System Error LED illuminated red. LCD displays "Internal UPS Fault" or a constant tone alarm. The alarm stops when the Power ON/OFF button is pressed for two seconds (this performs an Error Reset).
What it means: The UPS has detected an internal electronics failure. This is the most serious alarm the Smart-UPS can generate. In its severe form, the UPS stops supplying power and equipment loses protection.
What to do:
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Do not continue to use the UPS.
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Press and hold the Power ON/OFF button for two seconds to acknowledge and reset the error display.
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Attempt a controlled restart - if the fault clears and does not return, document it and monitor closely.
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If the fault persists after a restart, unplug the UPS and contact a service technician. This is not a user-serviceable condition.
Fault 3: Overload
What it looks like: Overload LED or icon illuminated. Continuous audible alarm. If overload is severe, the UPS transfers to bypass immediately.
What it means: The connected load exceeds the UPS's rated output capacity. The Smart-UPS cannot sustain this condition and will transfer to bypass, leaving equipment unprotected.
APC Smart-UPS overload response:
What to check:
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The LCD load bar shows current load as a percentage of rated capacity. Navigate to Status > Load to see the exact figure.
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Disconnect non-essential equipment immediately - printers, monitors, and secondary peripherals are the first to unplug.
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If load consistently exceeds 80% of rated capacity, the UPS is undersized for the current environment.
Fault 4: Bypass Mode (Unplanned)
What it looks like: Bypass icon illuminated. Audible alarm may be active. Load is powered but the battery backup LED is off.
What it means: The UPS has transferred the connected load to raw mains power. Equipment is powered but has no power protection - a mains failure now causes an immediate outage.
The Smart-UPS enters bypass when:
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An overload condition is detected
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An internal fault forces a safe fallback
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The bypass switch on the rear panel has been manually activated
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A remote bypass command has been issued via software
What to check:
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Check the rear panel bypass switch - if it has been moved to the bypass position, return it to normal.
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Check the LCD for an overload or fault condition that may have triggered the bypass.
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Navigate to Control > Turn On UPS or power cycle the unit to attempt a return to online mode.
Fault 5: Site Wiring Fault
What it looks like: LCD displays "Site Wiring Fault" or code G.00. The UPS continues to operate but logs the condition.
What it means: The Smart-UPS has detected one or more of the following electrical faults at the input connection: missing earth, hot and neutral wires reversed, polarity reversal, or overloaded neutral circuit. This is a fault in the building wiring - not the UPS itself.
What to do:
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Do not attempt to correct the wiring yourself. Contact a licensed electrician to inspect the circuit.
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The site wiring fault detection on the Smart-UPS applies to 230V Australian installations. The fault will persist until the underlying wiring issue is corrected.
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This alarm cannot be cleared by resetting the UPS - it will reappear every time the unit starts while the wiring fault exists.
Fault 6: On Battery (Extended)
What it looks like: Amber "On Battery" LED. Audible beep four times every 30 seconds.
What it means: This is normal operation during a mains power failure. However, if the UPS is running on battery with utility power connected, this indicates a different problem - the input circuit breaker may have tripped, or there is a severe input voltage or frequency distortion that the UPS cannot accept.
What to check:
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Verify that mains power is present at the socket.
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Check the UPS input circuit breaker on the rear panel - if it has tripped, reduce the load and reset it.
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If mains voltage is present but the UPS remains on battery, check the input voltage on the LCD. If it reads significantly outside the 220-240V range, the UPS is rejecting the input and running from battery. This can happen on generators with poor voltage regulation.
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Reduce the UPS input sensitivity via Configuration > Sensitivity if the unit is installed behind a generator or in an environment with unstable voltage.
Fault 7: AVR Boost / AVR Trim
What it looks like: AVR Boost or AVR Trim icon on the LCD.
What it means: The Smart-UPS is actively correcting the input voltage using its Automatic Voltage Regulation circuit. This is normal operation - the UPS is doing its job and the battery is not being used. AVR Boost corrects low voltage; AVR Trim corrects high voltage.
If the UPS is in AVR mode continuously, it indicates persistent voltage instability on the mains supply. This is common in older buildings, regional areas with aging grid infrastructure, and sites using small generators.
When to Call a Technician
The following conditions on an APC Smart-UPS require a qualified service technician:
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Internal fault alarms (P.xx codes) that do not clear after a single restart
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Constant tone alarm that returns after pressing the Error Reset
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Inverter error (P.13), output relay error (P.08), or AVR relay error (P.06)
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Battery voltage sensor error (b.12) or battery overtemperature (b.07)
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A UPS that enters bypass repeatedly without an obvious overload cause
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Any situation requiring internal component access beyond the battery door
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Site wiring faults (must be a licensed electrician)
Indigi Power & Cooling provides UPS maintenance and servicing for APC Smart-UPS systems across Brisbane, Sydney, Melbourne, and regional Australia. Our technicians carry genuine APC replacement battery cartridges for the full Smart-UPS range and can perform on-site fault diagnosis, battery replacement, and full preventative maintenance. If your Smart-UPS is showing a fault you cannot resolve, contact us or call 1800 046 344.
Get Your APC Smart-UPS Serviced by a Specialist
A fault alarm on your APC Smart-UPS is your UPS telling you it needs attention. Ignoring it risks unexpected downtime, corrupted data, and a battery that fails during the next power event.
Indigi Power & Cooling is an APC-experienced UPS service provider based in Brisbane, servicing organisations across Queensland, New South Wales, Victoria, and regional Australia. Our licensed technicians carry genuine APC replacement battery cartridges (RBCs) for the full Smart-UPS range, from the SMT 750 through to the SRT 10kVA, and can be on site for routine maintenance or urgent fault response.
APC Smart-UPS Battery Replacement
VRLA batteries in the APC Smart-UPS typically last 2-4 years depending on ambient temperature and discharge history. Australian summer temperatures accelerate degradation significantly. We supply and install genuine APC replacement battery cartridges for the full Smart-UPS range - the correct RBC number for your unit is printed inside the battery door.
APC Smart-UPS Preventative Maintenance
A structured annual maintenance visit covers battery impedance testing, full load transfer test, thermal imaging of connections, firmware version check, error log review and clearance, and a written service report. Finding a degraded battery before it causes a failure is the entire point of the exercise.
Fault You Cannot Resolve? Call Us Now.
If your APC Smart-UPS is showing an active fault, is stuck in bypass, or is no longer providing battery protection, call our team directly.
1800 046 344
admin@indigipc.com.au
Brisbane, Sydney, Melbourne and regional Australia.
Indigi Power & Cooling is an Indigenous and Veteran-owned Australian business. Supply Nation and ICN Gateway registered.
