P0A00: Motor Electronics Coolant Temperature Sensor A Circuit
What to do
Expect reduced power, since the car limits what the electronics may do when it cannot confirm they are being cooled. Do not top up any coolant reservoir without being certain which system it belongs to — a hybrid has two, they take different coolant, and they are easy to confuse. If in doubt, leave it to the workshop.
What this code means
A fault in the sensor measuring coolant temperature in the power electronics circuit. The first thing to establish about this code is which cooling system it refers to, because a hybrid has more than one and they are not interchangeable.
A hybrid typically carries two entirely separate coolant circuits: the engine's, which runs at the usual ninety degrees or so, and a low-temperature circuit for the inverter, converter and drive motor. Power electronics tolerate far less heat than an engine does — the semiconductors that switch hundreds of amps are the limiting component — so the second circuit runs much cooler and has its own radiator, its own reservoir and its own electric pump.
That separation matters practically, and not only to a workshop. The two reservoirs sit under the same bonnet, look similar, and take different coolant. Topping up the wrong one is an easy mistake with expensive consequences, and it is worth knowing which is which before opening either.
With this sensor unreadable the module cannot verify that the electronics are being cooled, so it protects them the only way it can — by limiting how hard they are allowed to work.
Likely causes
Start here
- Faulty inverter coolant temperature sensor · moderate
- Corroded or loose connector · easy
- Low inverter coolant level · moderate
Less common
- Open circuit in sensor wiring · moderate
Rare
- Faulty power inverter · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0A00.