If your AED’s self-test has failed, the device is working exactly as designed. The self-test runs automatically, finds a problem, flags it, and waits for someone to notice. That is the entire system doing its job. The failure is not the machine breaking down — it is the machine telling you something needs attention before it actually breaks down when it matters.
What you do in the next 24 to 48 hours is what separates a program that handles this correctly from one that doesn’t.
An AED with a failed self-test is out of service until the issue is resolved and the device clears a follow-up self-test. The two most common causes are expired or disconnected electrode pads and a depleted or expired battery — together accounting for nearly half of all real-world AED failures according to FDA adverse event data. Both are fixable in under 15 minutes. The third possible cause, an internal hardware or firmware fault, is less common but requires manufacturer support rather than a supply swap.
What an AED self-test actually checks
Understanding what the self-test looks at makes troubleshooting significantly faster — you know exactly where to look first. The Zoll AED Plus administrator’s guide documents the most specific publicly available list, and it’s representative of how all modern AEDs approach self-testing:
- Defibrillation electrode connection — verifies the electrode cable and pads are properly connected to the device
- ECG circuitry — verifies signal acquisition and processing electronics are functional
- Defibrillator charge and discharge circuitry — verifies the internal electronics can charge and discharge at rated energy
- Microprocessor hardware and software — verifies the AED’s processor and software integrity
- CPR circuitry and sensor (on models with CPR feedback) — verifies compression depth detection
- Audio circuitry — verifies voice prompts are functional
- Battery voltage and capacity — verifies sufficient charge to power operations
If any of these checks falls outside acceptable parameters, the self-test fails and the status indicator flips from ready to fault.
What the self-test cannot check (the part most guides miss)
This is the insight most articles on this topic skip, but it matters for understanding both why the self-test fails and why monthly manual inspections still matter even when the self-test passes.
⚠ Pad gel integrity
The self-test confirms the pad cable is connected and the circuit is intact. It cannot assess whether the conductive gel has dried out or lost adhesion — gel state doesn’t affect the electrical continuity test. A pad with significantly degraded gel can pass the connection check and still fail to adhere properly during a rescue.
⚠ Full capacitor charge/discharge verification
The self-test checks that charge circuitry responds correctly but cannot actually charge to full energy and discharge — doing so would deplete the battery for every test cycle. This means capacitor or high-voltage discharge damage can theoretically go undetected until actual rescue use.
⚠ Physical damage and accessories
The self-test checks internal electronics. It does not detect a cracked housing, a cabinet alarm that has stopped working, moisture damage, a missing rescue kit, or corrosion from heat or humidity. These conditions can coexist with a perfectly passing self-test.
Key implication: A passed self-test is necessary but not sufficient. Monthly manual inspection — walking up to the device, reading the indicator, physically checking pad and battery dates, inspecting the rescue kit — remains essential even when the self-test is passing cleanly.
The most common causes of a failed self-test
Based on FDA adverse event data from the MAUDE database, battery and power problems account for roughly 23% of AED failures and pad/connector issues account for another 24%. Together these represent nearly half of all real-world AED malfunctions — and both are directly what the self-test is checking.
✕ #1 — Expired or disconnected electrode pads (check first)
The pad cable can work itself slightly loose from the connector, especially in units that are moved or bumped regularly. Pad circuitry also shows as a fault when pads are expired, because gel’s electrical properties change as it ages and some devices detect this during the pad connection check. In programs using Zoll AED Plus units, pad cable disconnection from inspection or cabinet maintenance is the most commonly reported false alarm.
✕ #2 — Depleted or expired battery
Battery voltage drops below the threshold the device requires for self-test functions. On most models, the fault shows as low battery with some reserve remaining. On others, the voltage has dropped enough that the device can no longer complete the charge circuit check.
⚠ #3 — Zoll AED Plus mixed cell issue (brand-specific)
Unique to the Zoll AED Plus: the device runs on 10 Type 123 lithium batteries simultaneously. If cells are replaced individually rather than all 10 at once, the mixed charge state triggers a self-test failure even when most batteries are fresh. This is the specific, predictable Zoll failure mode that trips up programs that don’t know the “replace all 10 together” rule.
⚠ #4 — Defibtech 9-volt pilot cell failure (brand-specific)
The Defibtech Lifeline battery pack contains two power sources: the main lithium battery and a 9-volt cell that powers the self-test circuitry. If the 9V cell dies, the device fails self-test even with a healthy main battery. This produces the 7010 service code and is frequently mistaken for a full battery failure when only a $10–$12 9V cell needs replacement.
⚠ #5 — Temperature exposure outside rated range
AEDs stored in unheated cabinets over winter, in direct sun, or in humid environments (near pools, kitchens, loading docks) experience battery voltage drops that trigger self-test failures. The battery may be fully within its rated lifespan but insufficient voltage at low temperature.
↗ #6 — Internal hardware or firmware fault (less common)
If replacing pads and the battery doesn’t clear the failure, the device has an internal issue. This requires manufacturer service and is not user-fixable.
💡 AED Log fires battery and pad expiration alerts 60 and 30 days ahead — so self-test failures from predictable expirations don’t happen.
Fix steps by brand (what to do right now)
Philips HeartStart OnSite & FRx
Fault signal: Green ready light OFF + blue “i” button flashing + chirping
- Press the flashing blue “i” button briefly. The device speaks the specific fault out loud — most common messages are “Replace battery” and “Pads cartridge expired” or “Pads cartridge damaged.”
- Act on what you hear. Replace the M5070A battery or the SMART Pads cartridge as directed.
- Wait for the automatic self-test. After replacement, the device runs a self-test automatically. Wait for the green ready light to begin flashing before returning to service.
- If the “i” button isn’t flashing and the green light is simply off with no chirp, the battery is likely completely dead or absent. Insert a fresh M5070A battery and wait for the self-test to complete.
Zoll AED Plus
Fault signal: Red X in status indicator window (left side of handle) + possible beeping every minute
- Check the electrode cable connection. Unplug it and firmly reconnect it.
- Press and hold the ON/OFF button for more than 5 seconds to initiate a manual self-test. Listen for the voice message — “Change Batteries” or “Plug In Cable” — to identify the specific cause.
- Replace all 10 Duracell Type 123 batteries simultaneously if directed. Never replace a subset. Press the Battery Reset button inside the battery compartment after loading fresh batteries.
- Turn the device on and wait for “Unit OK” before returning to service. Confirm the status indicator window shows a green checkmark.
- If the red X persists after a fresh 10-pack and electrode reseating, contact Zoll Technical Service at 1-800-348-9011 with the device serial number.
Cardiac Science Powerheart G3
Fault signal: Rescue Ready indicator on handle turns red + intermittent audible beep
- Open the lid. The diagnostic panel under the lid shows which specific component triggered the failure. Match the lit indicator to the troubleshooting table in the owner’s manual.
- Check pad expiration date first, then battery manufacture date. Address whichever component is at fault.
- Close the lid to trigger a self-test. If the indicator returns to green, the device is ready.
- If the indicator stays red after replacing components, contact Cardiac Science Technical Support (24 hours) with the device serial number.
Cardiac Science Powerheart G5
Fault signal: Readiness indicator (top right corner) turns red with cross displayed + beeping
- Check pad expiration date, then battery date. Replace whichever is expired or suspect.
- If components are in date and the indicator stays red, press both grey buttons on the dashboard simultaneously to enter Diagnostics Mode. The device speaks the specific fault.
- Contact Cardiac Science with the spoken fault code and serial number if the issue doesn’t resolve with component replacement.
Stryker LifePak CR2
Fault signal: Green Readiness indicator stops flashing + alert tone every 15 minutes (no red light)
- Check the battery expiration date (printed to the right of the hourglass symbol in the battery compartment). Check whether the Charge-Pak has reached its expiration date.
- Replace the expired component.
- For diagnostic detail: open the lid, then press and hold the Language and Child Mode buttons simultaneously until the device speaks “Device Ready” or “Device Not Ready” followed by specific instructions.
Stryker LifePak CR Plus
Fault signal: Wrench icon on readiness display
- Check the Charge-Pak expiration date. The Charge-Pak bundles battery and pads — if expired, replace the entire Charge-Pak. Batteries and pads cannot be replaced separately on this model.
- Confirm the replacement Charge-Pak is fully seated. The OK symbol should return to the readiness display.
Defibtech Lifeline (DCF-100 and variants)
Fault signal: Red status indicator light + chirping tone
- Press the power button briefly. The device speaks the specific fault code. Listen to the full message before acting.
- Check pad connection first. Unplug and firmly reseat the electrode cable.
- If the fault message references the battery, check the main battery pack date. If the pack is within its rated life, check the 9-volt pilot cell inside the pack — the 7010 service code specifically points to the 9V cell. Replacement battery packs (DBP-1400, DBP-2800) include a fresh 9V pre-installed.
- Run a manual self-test: hold the power button until the device announces “Performing unit self-test.” In most cases it announces “Unit OK” once the component issue is resolved.
HeartSine Samaritan PAD (350P, 360P, 450P)
Fault signal: Status indicator flashing red + chirping tone
- Check the Pad-Pak expiration date. The Pad-Pak is a combined battery and pad cartridge with a single expiration date. If expired, replace the entire Pad-Pak.
- If the Pad-Pak isn’t expired but the indicator is flashing red, the battery within the Pad-Pak may have depleted before its listed date. Replace the Pad-Pak regardless.
How to confirm the fix worked: running a manual self-test
After replacing any component, confirm the fix worked before returning the device to service. Don’t assume a fresh battery means the device is ready.
| Brand | How to trigger a manual self-test |
|---|---|
| Philips HeartStart OnSite/FRx | Remove and reinstall the battery — device self-tests on installation |
| Zoll AED Plus | Press and hold ON/OFF button for more than 5 seconds |
| Zoll AED 3 | Press and hold ON/OFF button for 5 seconds |
| Cardiac Science Powerheart G3 | Open and close the lid |
| Cardiac Science Powerheart G5 | Open and close the lid; or press both grey diagnostic buttons |
| LifePak CR2 | Hold Language and Child Mode buttons simultaneously after opening lid |
| Defibtech Lifeline | Hold power button until unit announces self-test beginning |
| HeartSine Samaritan PAD | Install new Pad-Pak — device self-tests on installation |
LifePak CR2 caveat: Stryker’s documentation notes that running a manual self-test on the CR2 depletes battery capacity by the equivalent of one shock. Acceptable for occasional confirmation testing, but not for routine verification that would be better served by reading the green indicator.
What to do if the self-test keeps failing after you’ve replaced everything
A persistent self-test failure after both the battery and pads have been replaced points to an internal hardware or firmware fault. This is not user-serviceable.
- Tag the device OUT OF SERVICE with a physical label.
- Contact the manufacturer’s technical support with the device serial number and model:
Philips1-800-263-3342Zoll1-800-348-9011Cardiac Science1-800-426-0337Stryker (LifePak)1-800-722-9377Defibtech1-203-975-8000
- If the device is under warranty (most AEDs carry 7 to 10 year device warranties), repair or replacement may be covered.
- If the device is beyond warranty and beyond its expected useful lifespan (8 to 10 years), this is a natural replacement trigger, not a repairable fault.
Can you use an AED that’s failed its self-test during an actual cardiac arrest?
Yes. Attempt to use the device if it’s the only one available. A failed self-test means the device found a problem it can check — not that the device is completely dead. The battery may have enough reserve to deliver shocks even though voltage dropped below the self-test threshold.
⚠️ What you cannot count on: The impedance check the device runs before delivering a shock may fail, and the device may not advance to the shock step. If that happens, start continuous chest compressions and do not stop while waiting for EMS or another device. The goal of catching a failed self-test during a monthly inspection is specifically to prevent this scenario from ever happening.
The wider failure this flag reveals
A single AED failing its self-test is a fixable problem. What it sometimes reveals is a larger tracking problem underneath it. If the failure came from a battery that had been approaching its date for 6 months, the monitoring system didn’t catch a known, predictable event. If it came from pads that expired while the device was in a remote location nobody inspected monthly, the inspection cadence broke down.
Neither of these is a dramatic failure. They’re the normal outcome of managing AED maintenance with a reminder in someone’s calendar and a paper log on the cabinet, which works fine for one or two devices and breaks down reliably past five.
Battery Tracking and AED Inspections in AED Log are specifically built around catching these events before the self-test has to. Battery and pad expirations trigger alerts 60 and 30 days ahead. Monthly inspection reminders go to the named responsible person on a fixed date. Every completed inspection is timestamped and logged — so when a self-test fails, the audit trail shows whether this was a known approaching expiration or an unexpected fault, which is information an insurance carrier or compliance auditor will ask for. Pricing is based on the number of AEDs in your program, starting free on 1 AED.
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