The AM2 fuse blowing unexpectedly and repeated inverter overheating are two classic red flags that the Prius inverter coolant pump is not doing its job. In real-world diagnostics, these symptoms usually show up after the cooling loop has already been compromised for a while—meaning the safest and cheapest outcome comes from acting quickly, not “waiting to see if it goes away.”
Hybrid systems are remarkably durable when they stay within their intended temperature range. But once heat management fails, damage can cascade: an inexpensive pump issue can become an inverter failure, a fuse problem can become a stalling event, and intermittent warning lights can turn into a no-start condition. The goal of this guide is to help you understand what the inverter pump actually does, how to recognize failure symptoms early, how to verify the pump’s operation correctly, and how to think about repair cost and recall coverage like a professional—without wasting money on guesswork.
Important note before we begin: the Prius inverter loop deals with high-voltage components. You do not have to touch high-voltage wiring to diagnose the pump, but you should still treat the area with respect. If you’re uncomfortable around hybrid systems, have the inspection performed by a technician experienced with Toyota hybrids.
What is the purpose of the inverter pump?
To understand why the inverter pump matters so much, you first need a clear picture of what the inverter does in a Prius.
What is an inverter on a Prius vehicle? The inverter converts the DC current coming from the Hybrid battery and converts it to a higher voltage.
And it also converts electricity from a higher voltage to a lower voltage. Since the inverter works directly with electricity, it retains a lot of heat.
That description is accurate in principle, and here is the more detailed technician-level version: the inverter assembly in a Prius is not a single “box.” It is a group of power electronics that manage energy flow between the high-voltage (HV) battery, the motor-generators (MG1 and MG2), and the 12-volt electrical system. It performs multiple tasks:
- DC-to-AC conversion: the HV battery stores energy as DC, but the electric motor-generators operate on AC. The inverter creates and controls that AC power.
- AC-to-DC conversion (regeneration): when the vehicle is slowing down, the motor-generators act like generators, producing AC that must be converted back to DC to recharge the HV battery.
- DC/DC conversion: the inverter/converter assembly also supports the 12V system (charging the 12V battery and powering accessories) by stepping voltage down appropriately.
Every one of these conversions creates heat. Power electronics are efficient, but not perfect—especially under load, in hot weather, or during sustained high-speed driving. That heat must be carried away consistently. If it is not, the system protects itself by reducing power, logging fault codes, and in some cases shutting down to prevent more severe damage.
If there is no way to cool down the inverter, then it will overheat. So that’s where the Prius inverter pump comes in.
The main purpose of the inverter pump is to circulate coolant to the inverter and its many components. The coolant will draw away heat from the inverter and prevent it from overheating.
Think of the inverter coolant pump as the heart of a dedicated cooling loop. Unlike the engine cooling system (which manages engine temperature), the inverter loop is primarily there to protect expensive electronics. If the pump stops moving coolant—or if air gets into the loop and circulation becomes weak—temperatures rise rapidly during normal driving. Toyota’s hybrid control logic may then limit performance or force a shutdown to prevent catastrophic failure.
Also, when there is an issue with the inverter pump, the Prius computer system will display the diagnostic code. The diagnostic warning code for an inverter pump issue is P0893.
In practice, the code most technicians associate with inverter cooling performance problems on Toyota hybrids is commonly P0A93 (Inverter “A” Cooling System Performance). The “P0893” reference is frequently the result of misreading, miscoding, or an incorrect association in informal notes. The key takeaway remains the same: when the Prius detects that inverter cooling performance is not meeting requirements, it stores a diagnostic code that must be read with a scan tool capable of hybrid data. Some vehicles and scan tools may also show related subcodes (“INF” codes) that refine whether the issue is pump-related, coolant flow-related, or sensor-related.
As an owner, you do not need to memorize every code. You need to understand that the warning light is the symptom, and the code is the diagnosis. The code tells you where to focus your inspection, which is the difference between replacing one pump and replacing half the inverter assembly unnecessarily.
Prius inverter pump failure symptoms
Any vehicle can break down for any reason. The inverter pump is an important part of a Prius.
If it is not working as it should, there will be obvious signs that you will notice in no time.
When there is an issue with the inverter pump, your Prius will activate the check engine light. It may also turn on a different light which will look like a yellow triangle. Inverter pump issues are not something that should be ignored.
From a diagnostic standpoint, inverter pump issues usually present in a predictable pattern. To make this easier to interpret, here are the most common symptoms, rearranged from “most critical safety consequence” to “supporting evidence.”
- Sudden stall or shutdown (especially if the AM2 fuse blows or inverter protection logic cuts power)
- Master warning / triangle warning light and/or Check Engine Light, often accompanied by hybrid system warnings
- Loss of hybrid power, reduced acceleration, or limp behavior after the vehicle warms up
- Inverter overheating during highway driving, hot weather, or heavy acceleration
- Coolant in inverter reservoir shows no movement when the car is READY
- Intermittent warning lights that reset after cooling down (classic thermal pattern)
Now let’s break down the “headline” symptoms described in your original notes, and add the practical reasoning behind each one.
The inverter keeps overheating.
When the Prius pump does not work as it should, it will not be able to circulate coolant to the inverter and to other components in the system. Since cooling cannot reach these parts, the inverter will overheat. Then the check engine light will turn on.
This sequence is a textbook example of how hybrids protect themselves. When coolant flow stops (or becomes too weak due to air pockets, blockages, or pump failure), heat accumulates inside the inverter assembly. The system may:
- Reduce electric assist to lower inverter load
- Trigger warning lights and store DTCs
- Enter a limited-power mode
- In extreme cases, shut down to prevent damage
What makes overheating so dangerous is that it often does not feel dramatic at first. Many owners notice only a warning light, then continue driving. But power electronics can be damaged quickly by sustained heat. Once that happens, the repair isn’t “replace a pump”—it becomes “repair or replace the inverter assembly,” which is a much more expensive job.
Professional tip: overheating often follows a pattern. If your Prius drives normally for the first 10–20 minutes, then begins throwing warnings after the system is heat-soaked, that thermal timeline is a strong indicator that cooling performance is deteriorating rather than a random sensor glitch.
Inverter pump sensors do not work
Sensors around the inverter and inverter components send information to the main module of the Prius’ computer. The computer then commands the inverter pump to pump coolant to cool down the inverter.
If the sensors do not pick up on the heat of the inverter, the inverter pumps will not pump coolant to cool down the inverter.
It could be that the sensors fried because of the inverter overheating one or two times. The sensors have to be replaced.
This section captures an important concept, but it’s worth clarifying how Toyota typically designs these systems. On most Prius generations, the inverter coolant pump is expected to run when the car is in READY (though exact logic varies). The pump is not always “commanded on only when hot” like an engine fan might be. Instead, Toyota tends to circulate coolant continuously or semi-continuously to keep inverter temperature stable and predictable.
That said, sensors still matter. The hybrid control system uses temperature sensors and other feedback to decide how much load is safe. If a sensor is inaccurate (or wiring is compromised), the ECU may interpret conditions incorrectly—either underestimating heat (risking damage) or overestimating heat (causing unnecessary power limits and warnings).
In a real repair scenario, “sensors do not work” can mean several different things:
- Sensor failure: the sensor itself is out of range or intermittently drops out.
- Connector or harness issue: corrosion, loose pins, water intrusion, or vibration damage.
- Thermal damage: repeated overheating can degrade plastics and electrical insulation, making failures more likely over time.
- Air in the coolant system: temperatures spike because coolant isn’t actually flowing correctly, making the sensor “look bad” when it’s simply reporting a real problem.
So yes—sensors may need replacement in some cases, especially after overheating events. But as a diagnostic strategy, a professional will confirm whether the sensor is wrong or the cooling system is wrong by comparing scan data, physical coolant movement, and temperature behavior under controlled conditions.
The am2 fuse blows out
The scariest aspect of the am2 fuse blowing out randomly is that when it blows, your Prius will immediately stall. You could be on the freeway and it will start shutting down out of nowhere. So why does the am2 fuse blow out?
One reason why the am2 fuse shorts out, especially in Prius, is because the inverter becomes too hot. When you check on the fuse, the metal side pieces will have a light burnt color.
You can replace the fuse, but you must find the reason why the inverter pump is not working. If you simply replace the fuse and don’t check on the pump, the am2 fuse will blow again.
This is one of the most important real-world warnings in the entire article. An AM2 fuse event can turn a repair into a safety incident because stalling at speed is dangerous. The “why” matters, and it’s usually not that the fuse “randomly decided to fail.” Fuses open because the circuit experienced abnormal current flow—often due to an overload, short, or component failure.
In Prius diagnostics, AM2 fuse issues can relate to electrical faults that may be influenced by heat and inverter system stress. If the inverter overheats repeatedly, you can see abnormal electrical behavior that contributes to fuse problems. That’s why replacing the fuse without investigating cooling and inverter health is a short-term reset, not a solution.
From an expert perspective, the correct approach is:
- Replace the fuse with the correct rating (never “upsize” a fuse to stop it blowing—this can create a fire risk).
- Pull hybrid and powertrain codes with a Toyota-capable scan tool.
- Verify coolant movement and pump operation in READY mode.
- Inspect inverter coolant level and signs of air (gurgling, inconsistent reservoir level, no flow).
- Confirm no harness or connector damage around inverter/pump circuits.
In other words, the AM2 fuse is not merely a “parts store problem.” It is a diagnostic clue that points to a system condition that must be corrected—often involving heat management and component reliability.
How to check a Prius inverter pump
Turn on your Prius and leave it in park. Wait a few minutes for the engine to warm up. Open the hood of your Prius and prop the hood open.
Locate a long and slightly orange container next to the Prius battery. Remove the small circular plug and look inside the water pump container. The water should be moving slightly.
This means the pump is not working and will not pump coolant into the system.
The inspection method above is a good starting point, but the last sentence needs one critical clarification. If the fluid is moving, that typically indicates the pump is circulating coolant. If the fluid is not moving (no turbulence, no visible flow), that strongly suggests the pump is not circulating coolant—either because the pump has failed, the system is air-locked, or circulation is blocked.
Here is the refined, expert-friendly step-by-step procedure that avoids common mistakes and makes the result easier to trust:
Step-by-step: visual coolant flow check (the fast test)
- Make the car READY. On most Prius models, the inverter pump runs reliably in READY. Accessory mode is not enough for consistent testing.
- Park safely. Parking brake on, transmission in Park, hood secured open.
- Locate the inverter coolant reservoir. It is often a translucent container with pink/orange coolant (Toyota Super Long Life Coolant is commonly pink).
- Remove the cap carefully. The system is not usually high-pressure like the engine system, but always open slowly and safely.
- Look for movement. You want to see gentle turbulence/flow in the reservoir. Some vehicles show obvious movement; others show subtle rippling—use good lighting.
- Listen and feel. A functioning electric pump often produces a faint hum/vibration. Carefully feel hoses for temperature change and flow response (avoid hot components).
Interpreting results:
- Visible movement = pump is likely running (still verify codes and temperatures if you have warnings).
- No movement = strong indication of pump failure, air in system, blockage, or electrical supply issue.
- Bubbling/foaming = possible air intrusion, improper bleeding after service, or leaks allowing air in.
For a more definitive test, technicians use scan data: inverter temperature values, pump command status (if supported), and cooling performance under controlled load. But the visual reservoir test is still one of the best “no-tools” checks a Prius owner can perform.
Common reasons the flow check can fool you
Even good tests can be misread. Here are the most common reasons owners get confused when checking inverter coolant movement:
- Car not in READY: in accessory mode, you may not see pump operation.
- Subtle flow: some reservoirs show only mild rippling; use a flashlight and look carefully.
- Air pockets: a pump can “spin” but move little coolant if air is trapped in the loop.
- Low coolant: low fluid level can reduce visible turbulence and increase the chance of sucking air.
- Recent service: after coolant replacement, improper bleeding can mimic pump failure symptoms.
If you see no movement and you have warning lights, don’t keep driving “to see what happens.” Confirm the issue and repair it before overheating damages expensive components.
Cost of replacing an inverter pump
The average price of an inverter pump is around $250. Now you must add the cost of labor. A typical mechanic will charge around $450 for the labor and the parts.
Those numbers are realistic as a baseline, but actual totals can vary widely depending on Prius generation, shop labor rate, local market pricing, and whether coolant replacement/bleeding is included. In many cases, the “real” cost difference isn’t just labor—it’s how accurately the shop diagnoses the issue and whether they replace only what’s needed.
To help you plan like an expert, here’s what usually makes the price move up or down:
- OEM vs aftermarket pump: OEM parts cost more but tend to have more predictable quality and fitment.
- Coolant included: proper service often includes topping up or replacing coolant, plus bleeding air from the system.
- Diagnostic time: a reputable shop will confirm the fault rather than replacing parts based on assumption.
- Additional issues discovered: leaks, corroded connectors, brittle hoses, or prior improper repairs can add cost.
If you take your Prius to a Toyota mechanic, they will find every opportunity to charge you more. But since they are trained by Toyota, they will know exactly how to fix your Prius.
They can also find out why the inverter pump stopped working and give you tips on how to care for it.
If you take your Prius to a non-certified mechanic, their prices may be cheaper.
You will have to find one that knows how to repair and care for hybrid vehicles as many mechanics still do not know how to do this. They won’t be able to tell you how to prevent your inverter pump from malfunctioning in the future.
From a professional standpoint, the best shop is not necessarily “dealer” or “independent.” The best shop is the one that can do three things consistently:
- Access Toyota hybrid codes and subcodes and interpret them correctly.
- Confirm coolant flow and thermal behavior before installing parts.
- Bleed and refill the inverter cooling loop correctly so the new pump isn’t immediately compromised by trapped air.
If a shop quotes you for an inverter pump but cannot describe how they will verify flow after repair, that is a red flag. Proper verification is not optional; it is how you ensure you’re paying once, not twice.
Why the Inverter Pump Fails (And How to Slow Down the Next One)
Owners often ask, “Why did the inverter pump stop working?” In many cases, it isn’t a single dramatic event. It’s slow wear combined with heat, age, coolant condition, and sometimes vibration or electrical issues.
Common failure contributors include:
- Internal electric motor wear: like any electric pump, bearings and internal components can fatigue over time.
- Coolant contamination: debris, corrosion byproducts, or degraded coolant can reduce pump efficiency and harm internal seals.
- Air in the system: air pockets reduce cooling effectiveness and can cause noisy operation and poor flow.
- Electrical supply issues: poor connectors, corrosion, or harness strain can cause intermittent pump operation.
- Heat stress from prior overheating: once the inverter loop has overheated, components in the area become more vulnerable.
Prevention isn’t complicated, but it does require consistency:
- Maintain coolant condition. Use the correct Toyota-specified coolant and service interval guidance for your model.
- Fix small leaks early. Low coolant invites air, and air kills cooling performance.
- Take warning lights seriously. A hybrid system that limits power is telling you it’s protecting expensive parts.
- After any coolant service, confirm flow. The job is not complete until circulation is visually verified and codes are cleared properly.
Most inverter pumps don’t fail because owners “did something wrong.” They fail because all mechanical/electrical parts eventually wear. The key is catching the early signs before the pump failure drags other components down with it.
Professional Diagnostic Checklist (What a Hybrid Technician Looks For)
If you want to think like a technician, use this checklist. It helps you avoid the most common misdiagnoses and focuses attention on the highest-value verification steps.
1) Confirm the car is logging hybrid-related cooling codes
A weak 12V battery can cause confusing errors, and unrelated codes can coexist. Before replacing any inverter cooling parts, read the stored diagnostic codes with a scanner that supports Toyota hybrid systems. If you only have a generic reader, you may miss key hybrid ECU codes.
If a code indicates inverter cooling performance, that supports the pump diagnosis. If codes point elsewhere, the pump may be a secondary symptom rather than the cause.
2) Verify coolant level and look for signs of air
Low coolant can mimic pump failure. Air pockets can mimic pump failure. A quick visual inspection of the inverter coolant reservoir level and condition is one of the simplest steps that prevents expensive mistakes.
Signs that air may be present include fluctuating level, gurgling noises, and inconsistent heat behavior. Air matters because it reduces heat transfer and may prevent the pump from circulating coolant effectively.
3) Verify actual flow at the inverter reservoir (READY mode)
This is the “trust but verify” moment. The pump can fail electrically, mechanically, or intermittently. Flow confirmation tells you whether circulation is happening right now. If there’s no flow, do not assume the inverter is safe to keep driving.
4) Inspect pump electrical connector and harness routing
Before you condemn the pump, confirm the pump is actually receiving power and that its connector isn’t corroded, loose, or damaged. In many real repairs, a connector issue creates intermittent pump operation that looks like “random overheating.”
5) Confirm post-repair circulation and temperature stability
The repair is not complete when the part is installed. The repair is complete when:
- Coolant flow is visible in READY mode
- No air pockets remain (system is properly bled)
- Codes are cleared intentionally and do not return
- Inverter temperatures stabilize under normal driving load
This post-repair verification is the difference between a professional fix and a repeat failure.
Prius Inverter pump Recall
In 2018, the Toyota motor engineering Factory sent out a recall notification to certain Toyota Prius models. The models were between 2010 and 2014 for the Toyota Prius and 2012 to 2014 for the Toyota Prius 5.
The reason the Toyota company sent out recall notifications was that these vehicles were installed with faulty power inverters.
The main issue with the power inverters was that the system allowed too much electricity to flow through the IPM or the intelligent power module.
This issue caused Prius and Prius 5 to shut down. If you own a Prius and Prius 5, you may have been driving with a faulty inverted pump or faulty inverter.
There’s also a separate recall in 2009 specifically for the inverter pump. It appears that it was common for inverter pumps to fail in second-generation Toyota Priuses.
Many of the inverter pump failure questions and information on the internet pertain mostly to the second-generation Priuses. It seems like it is an ongoing issue.
The reason why these inverted pumps had to be recalled is that the pumps allowed air inside the coolant system.
There would be sections of the coolant system that only pumped air, not coolant. Air in the coolant pump system means that the system could not cool down the inverter.
Here is the expert-friendly takeaway from the recall discussion above: not all Prius inverter-related recalls are the same, and not all are strictly “pump recalls.” Some campaigns focus on the inverter’s power electronics (IPM behavior), while others target coolant pump reliability and air ingestion issues. Both matter because both can lead to shutdown events.
If you suspect your Prius is affected, the best practice is to do three things:
- Check recall status by VIN using official resources or a dealer inquiry.
- Confirm whether the repair was performed (some vehicles change owners and repairs are missed).
- Do not confuse “inverter recall” with “pump failure.” A recalled inverter campaign may not fix a mechanical pump that is currently failing, and a pump recall does not fix IPM transistor stress.
Understanding that difference prevents a common owner mistake: assuming a recall automatically explains today’s warning lights. Recalls provide useful context, but you still need current diagnostic codes to confirm the actual present-day fault.
Conclusion
The two most common symptoms of a failed inverter pump are the inverter overheating and the am2 fuse blowing out. You can check on the inverter pump by opening the pump container located in the middle of your Prius.
The cost to replace an inverter pump can be as high as $450. There have been several inverter pumps and inverter recalls in the last 10 years.
To wrap it up in the most practical terms: inverter pump problems are not worth ignoring. The pump exists to protect the inverter, and the inverter is one of the most expensive components in the hybrid drivetrain. If you catch the issue early—by confirming coolant flow, checking codes, and addressing air or pump failure—you usually prevent the most costly outcomes.
If you remember only one professional rule, make it this: verify coolant circulation in READY mode and read the stored codes before replacing parts. That combination keeps you safe, keeps the hybrid system reliable, and keeps your repair bill proportional to the actual problem.
