P0A78: Drive Motor A Inverter Performance
What to do
Do not accept an inverter quote on this code alone. In order, ask: has the inverter's own coolant loop been checked; has its supply and earth been tested; is there a software update; are there open recalls or service campaigns for this vehicle — that last one costs nothing to check and has covered this exact repair on some models.
What this code means
The inverter section driving the main motor is not performing as commanded — the module's broadest verdict on its most expensive electrical component.
Read the breadth of this code as its main content. "Performance" is what gets stored when the inverter's behaviour is wrong in a way none of the specific families — phase currents, current sensors, its own temperature — has already named. A broad code invites the broad conclusion, and the broad conclusion here is a four-figure inverter; that is exactly the sequence to resist, because the specific causes are cheaper and come first.
The checklist, cheapest first. The inverter's own cooling loop — an inverter running hot performs badly before it fails outright, and the loop's pump, level and air content are a five-minute check (P0A3C explains why the engine's coolant bottle proves nothing). Its twelve-volt supply and earth — the control side of the inverter is a module like any other, and the P0882 rule about undersupplied modules reporting phantom faults applies in full. Software — inverters have shipped with control-logic bugs, and several manufacturers have fixed exactly this code with an update; on some models the same behaviour has been the subject of recalls, so checking for open campaigns by chassis number is free and occasionally pays for the whole visit. The inverter itself is real as a failure, but it is the end of the list, not the beginning.
Likely causes
Start here
- Faulty inverter coolant pump · moderate
- Failed power or earth supply to the module · moderate
Less common
- Module software fault needing an update · specialist
- 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
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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.
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