P0A05: Motor Electronics Coolant Pump A Control Circuit/Open
What to do
Expect reduced power, since the car will not let the electronics work hard without cooling it can verify. If you have ever heard a soft whirring from the front of the car for a minute or two after switching off, that is this pump doing its job rather than a fault.
What this code means
A fault in the circuit controlling the electric pump that circulates coolant through the power electronics.
The pump is electric rather than belt-driven, and the reason is fundamental to how a hybrid works: the inverter does its hardest work when the engine is switched off. Pulling away on electric power alone means the inverter is handling full drive current with no engine running, so a belt-driven pump would be stationary at exactly the moment cooling matters most. An electric pump can run whenever the module says so, including with the vehicle stationary and silent.
That also explains a noise owners sometimes report and worry about: a soft whirring from the front of the car after it has been switched off and locked. That is usually this pump running on to remove residual heat from the electronics, and it is the system working correctly.
Likely causes
Start here
- Faulty inverter coolant pump · moderate
- Open circuit in pump wiring · moderate
- Corroded or loose connector · easy
Less common
- Blown fuse or failed supply · easy
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 P0A05.