Diagnostic trouble code
P0A93 — Inverter cooling system performance
What it means in plain English
Toyota hybrids run a dedicated coolant loop just for the inverter, with its own electric pump and reservoir. P0A93 indicates that this cooling circuit isn't performing as expected. It's an important code to recognise in Arizona because the symptom — a hybrid warning and reduced power on a hot day — looks exactly like a failing battery to anyone who doesn't check.
Which Toyota and Lexus models this applies to
Toyota and Lexus hybrids that use a dedicated inverter coolant circuit, which covers the Prius family and most Toyota/Lexus hybrids we service.
Possible causes
Plural on purpose. Any of these can produce this result — which is exactly why a code is not a diagnosis.
- A failing or failed inverter coolant pump.
- Low coolant in the inverter loop.
- Air trapped in the cooling circuit after a previous service.
- A restricted inverter cooler or radiator section.
- A wiring, relay or connector fault affecting pump operation.
- A coolant temperature sensor fault.
What a professional diagnostic process should check
- 1Check inverter coolant level and condition in the correct reservoir — it's separate from the engine coolant.
- 2Verify the inverter coolant pump actually runs and circulates coolant, rather than just checking that it's powered.
- 3Look for air in the circuit and bleed properly if the system has been serviced before.
- 4Inspect the inverter cooler/radiator section for restriction or debris — worth noting in a dusty climate.
- 5Check pump wiring, connector and relay.
- 6Confirm coolant temperature sensor readings are plausible.
What you can safely do now
- Check the inverter coolant reservoir level if you can identify it in your owner's manual — it's a separate reservoir from the engine coolant.
- Note whether the fault appears specifically on hot days or in slow traffic.
- Get it addressed before summer rather than during it.
- Mention any recent cooling system work, since trapped air is a real cause.
What not to do
- Don't top up with the wrong coolant. Toyota hybrids use specific coolant types and mixing them causes problems.
- Don't open any cooling system while it's hot.
- Don't accept a hybrid battery quote for a car whose only stored code points at inverter cooling.
- Don't keep driving in reduced power on a hot day — the system is protecting itself for a reason.
When towing or urgent service is appropriate
If the vehicle has gone into reduced power or is showing overheating-related messages, stop and have it towed. Continuing to drive an inverter that isn't being cooled properly risks turning a moderate repair into a very expensive one.
Not sure which category you're in? Call 623-323-0737 and describe what the car is doing. That call is free and it might save you a tow — or a much bigger repair.
Do not replace parts based on a code alone
Do not replace parts based on a code alone. A diagnostic trouble code tells you which circuit or system reported a problem — it does not identify which component failed. The same code can be set by several different faults, and clearing it without a diagnosis just hides the evidence. This page is educational; your vehicle needs its own inspection before any repair decision.
P0A93 — common questions
Is P0A93 a hybrid battery problem?
Why does this happen more in Arizona?
Can I just top up the inverter coolant?
Get P0A93 diagnosed properly
Tell us the code, the year and model, and what the car is doing. We'll tell you what we'd check — and we won't quote a repair from a code.
Not sure what your hybrid needs? Start with the free diagnostic.
We come to you, test the pack, the 12V and the cooling, and you get a written quote before anything is decided. No charge, no obligation.