Short version: P0A93 means Inverter “A” Cooling System Performance. Your Prius runs a separate cooling loop just for the inverter, the power electronics that drive the hybrid motors. P0A93 sets when that loop can’t move enough coolant to keep the inverter cool. On the 2004–2009 (Generation 2) Prius, the usual cause is a worn-out inverter coolant pump. Toyota even extended the warranty on it. It’s mostly a hot-weather, hot-car problem, so if the car cools off you can often limp it home. But an overheating inverter can shut down the DC-to-DC converter that charges your 12-volt battery. That’s why some owners see a battery light come on with it.
| Code | What it means | Most common cause we see | Typical fix |
|---|---|---|---|
| P0A93 | Inverter “A” Cooling System Performance — the inverter’s dedicated cooling loop isn’t keeping the inverter cool | A failing inverter coolant pump, especially on the 2004–2009 (Gen 2) Prius; low or old coolant and trapped air come next | Confirm the pump is genuinely moving coolant, then replace the pump (and the AM2 fuse if it shorted), or correct the coolant level, trapped air, or restriction — with a proper bleed |
What P0A93 means
The inverter is a box of power electronics. It takes high-voltage DC from the hybrid battery and turns it into the AC the drive motors need. When you brake, it runs the other way and helps recharge the battery. All that switching throws off a lot of heat. Air can’t carry it away fast enough, so the inverter gets its own liquid-cooling system, separate from the engine’s: a dedicated electric pump, a small radiator, and its own coolant.
P0A93 sets when the hybrid computer watches that loop and decides it isn’t keeping up. Maybe the coolant isn’t circulating. Maybe the inverter temperature won’t come down the way a healthy system brings it down. Either way, it’s a performance code, not a “replace this exact part” code. That’s why it needs a real diagnosis, not a guess.
Why P0A93 can turn on your battery light
This part surprises people. A Prius has no alternator. Instead, a DC-to-DC converter sits inside that same inverter assembly. It steps the high-voltage battery down to about 14 volts. That’s what charges your ordinary 12-volt battery and runs everything electrical in the car. So a part inside the inverter does the alternator’s job, and it shares the very same cooling loop.
When the cooling system fails and temperatures climb, the car protects the electronics. One way it does that is to shut the DC-to-DC converter down. The moment it stops, your 12-volt battery stops charging. It runs down like a flashlight, and the 12-volt battery / charging warning light comes on. Let it go long enough and the 12-volt system drops too low to run the car. Then it shuts off and won’t restart.
Here’s the connection a lot of owners miss. A battery light on a Prius isn’t always about the 12-volt battery itself. When it shows up next to P0A93, the battery isn’t the problem. The inverter cooling is, and the car shut the charging down to keep the inverter from cooking. (For how the 12-volt system works on these cars, see Why Your Prius or Toyota Hybrid Won’t Start: The 12V Battery Explained.)
What actually causes P0A93 on a Prius
Across the Priuses we’ve diagnosed for this code, the causes fall into a fairly clear order.
A failing inverter coolant pump — the big one on Gen 2. On the 2004–2009 Prius, the electric pump wears out and stops moving fluid. It’s common enough that Toyota extended the warranty on it. When the pump can’t keep coolant flowing, the inverter heats up and P0A93 sets. We check this first on a Gen 2. The shop video below shows how we confirm the pump is really doing its job.
Low or old inverter coolant. The loop can run low from a slow leak, or because nobody ever serviced it. The pink Toyota coolant also breaks down over years and miles. Too little coolant, or coolant that’s past its life, and the system can’t shed heat fast enough.
Air trapped in the cooling loop. This one catches people out. You have to bleed the inverter coolant system correctly. If an air pocket sits where coolant should be, the pump spins but moves no heat, and P0A93 comes right back. We see it after someone tops off or swaps the coolant and skips the bleed procedure. People blame the pump when the real culprit is air.
Less common causes
The pump’s electrical circuit. No power, a blown fuse, or corroded wiring will stop the pump just as surely as wear. So a good diagnosis confirms the car is actually commanding and powering the pump before condemning it.
A restriction in the loop. A kinked hose, a blockage, or a clogged inverter radiator can choke flow even with a good pump and fresh coolant. It’s less common, but real. That’s why we verify actual flow instead of assuming.
When the pump takes out the AM2 fuse
There’s a worse way this can go, and it doesn’t look like a cooling problem at all. Sometimes the pump fails by shorting internally instead of just wearing out. When it does, it can blow the AM2 fuse. That’s no ordinary fuse. AM2 is a main 15-amp feed. On the Gen 2 Prius it’s a genuine Toyota “ultra mini” fuse (part 90080-82052), not the standard mini fuse in a glovebox kit. So even swapping it isn’t a gas-station fix.
And when AM2 goes, it takes a lot with it. It cuts power to the Power Source Control ECU, often setting code B1210. The car simply dies, usually while driving, and won’t restart. There’s often a burnt-electronics smell around the fuse box by the driver’s-side headlight. Drop a fresh AM2 in and it can blow again the moment the shorted pump loads it up. The only real fix is to replace the pump and the fuse together. So a Prius that “just died and won’t start” can trace back to the same pump behind P0A93. It just took out a critical fuse on the way out.
Is it safe to drive?
Here’s the practical part, and it catches people off guard. P0A93 is mostly a hot-day, hot-car problem. The cooling only falls behind when there’s real heat to shed: a hot engine bay on a hot afternoon, stop-and-go traffic, a long climb. That’s when temperatures cross the line. The code sets, and the car may pull power back or shut the DC-to-DC converter down. Let everything cool off, and the same car often acts completely normal again.
So if this strands you in the heat of the day, you usually have options. Park it and let it cool down. Wait for the cool of the evening. Once the inverter isn’t fighting the heat, you can often limp it home at night. What you shouldn’t do is keep pushing it hot with the light on. The inverter is one of the priciest parts on the car, and it needs that liquid cooling. Without it, the inverter overheats and fails. Limping it home cool is fine. Daily-driving it with an active P0A93 is how a cooling problem becomes a new inverter. Get it diagnosed promptly instead of living with it.
How P0A93 should actually be diagnosed
The wrong move is to throw a pump at it and hope. The right sequence looks like this:
- Scan the whole car and read the data. With Techstream, Toyota’s factory software, we watch inverter temperature and cooling data live, not just the stored code. That tells us whether the system is failing right now or set the code once and recovered.
- Check the coolant, level and condition. Is the loop actually full? Is the coolant healthy or years past due? It’s quick, and it rules out the cheapest cause first.
- Confirm the pump is really pumping. This is the key step, and the one in the video below. Hearing the pump or seeing it get power isn’t enough. A pump can hum with power and still move no fluid, so we verify it’s genuinely circulating coolant.
- Rule out air and restrictions. If the pump checks out, we make sure no air pocket is trapped in the loop and nothing is choking flow. If anyone’s opened the system up, we bleed it properly.
Done in that order, you fix the real failure. You don’t pay for a pump the car never needed. And you don’t replace the pump only to have the code return because the real problem was air.
Our own shop video: checking whether the inverter coolant pump is actually circulating fluid on a Generation 2 Prius that set P0A93.
From the shop floor: The Gen 2 Prius earned this code so reliably that Toyota extended the warranty on the pump. But we still see shops replace the pump without checking for air, or without confirming the new pump actually moves coolant. Then P0A93 comes back, and the customer is out a part that wasn’t the whole story. Confirming real flow is the difference between fixing it once and chasing it twice.
Related reading from our shop
P0A93 sits alongside a few other Prius topics worth understanding:
- Why Your Prius or Toyota Hybrid Won’t Start: The 12V Battery Explained — how the DC-to-DC converter and the 12-volt battery work together.
- How We Diagnose Toyota Hybrid Problems: The 6-Step Process — the method behind reading data before replacing parts.
- The 2004–2009 Prius “Triangle of Death” — what the red triangle warning light really means on a Gen 2.
- Toyota Hybrid Trouble Codes — our index of the hybrid trouble codes we cover.
- Toyota Prius P148F00 Code Explained — the engine’s electric water pump code, a different cooling loop with its own failure patterns.
- Toyota Prius Catalytic Converter Theft: Which Years Are Targeted, and How a Cat Shield Helps — another risk for the same 2004–2009 Prius generation.
- The Hidden Danger Under Your Hood: How to Spot Counterfeit Toyota and Denso Parts — why a suspiciously cheap replacement pump can be worse than no repair.
Frequently Asked Questions
What does the P0A93 code mean on a Toyota Prius?
P0A93 is “Inverter A Cooling System Performance.” The inverter runs the hybrid drive motors, and it has its own cooling loop, separate from the engine’s. P0A93 sets when the hybrid computer decides that loop isn’t cooling the inverter enough. Most often, the inverter coolant pump is failing.
Why is my Prius battery light on with a P0A93 code?
A Prius has no alternator. A DC-to-DC converter inside the inverter charges your 12-volt battery, and it shares the inverter’s cooling. When the inverter overheats, the car can shut that converter down to protect it. The moment it stops charging, the 12-volt battery light comes on. The battery usually isn’t the real problem. The inverter cooling is.
Why does P0A93 only act up when it’s hot out?
The cooling system only works hard when there’s heat to remove. On a cool morning, the inverter can stay in range even with a weak pump or low coolant, so the car acts normal. Add a hot day, a hot engine bay, and stop-and-go traffic, and the temperature climbs past the limit. The code sets, and the car may pull power back or shut the DC-to-DC converter down. Let it cool and it often behaves again. That’s why the failure looks intermittent and is easy to dismiss until it strands you.
Can I keep driving my Prius with a P0A93 code?
Not as a daily driver. P0A93 is mostly a hot-car, hot-weather problem, so the car may act up in the afternoon and feel normal after it cools. If the heat catches you out, let the car cool and drive it home in the evening. That will often get you there. But an active P0A93 is a real cooling failure on a very expensive part. Limp it somewhere and get it diagnosed rather than living with it.
Why did my Prius suddenly die and blow the AM2 fuse?
On the Gen 2 Prius, a failing inverter coolant pump can short internally and blow the AM2 fuse. That’s a main 15-amp “ultra mini” fuse, not a standard mini fuse. When it goes, it cuts power to the Power Source Control ECU (often with code B1210) and the car dies, usually while driving, and won’t restart. You’ll often notice a burnt-electronics smell near the fuse box. A new fuse alone won’t hold if the pump is still shorted, so you replace the pump and the fuse together. It’s the same pump behind P0A93, just failing in a way that takes out a critical fuse.
What usually causes P0A93 on a 2004–2009 Prius?
On the Generation 2 Prius, the most common cause by far is a failing inverter coolant pump. Toyota extended the warranty on it because it happens so often. Low or old coolant, trapped air, a fault in the pump circuit, or a restriction in the loop can all do it too. So confirm the pump, don’t just assume it.
Is the inverter coolant the same as the engine coolant?
No. The inverter has its own cooling loop, with its own coolant, pump, and radiator, separate from the engine’s. It uses Toyota’s pink long-life coolant. You have to bleed the air out of it correctly when you service it. Skip that step, and P0A93 often comes back after a coolant or pump job.
How does Atomic Auto diagnose P0A93?
We scan the whole car and read the inverter’s live temperature and cooling data with Techstream. We check the coolant level and condition. Then we confirm the pump is genuinely moving fluid, not just getting power. If the pump checks out, we rule out trapped air and restrictions in the loop. That way the repair matches the real failure, instead of a guessed-at pump.
Seeing P0A93 on your Prius? Book online or text us at 503-969-3134.
About the author: Travis Decker is the owner of Atomic Auto in Portland, Oregon, and an ASE Master Technician (L1, L3). Atomic Auto specializes in Toyota, hybrid, and EV service.