P0A79: Drive Motor B Inverter Performance
What to do
As P0A78, including the recall check. On a rear-motor car, add the underfloor supply and coolant runs to the list of cheap things to inspect first.
What this code means
The inverter section driving the second motor is not performing as commanded.
P0A78's whole checklist transfers — cooling loop, supply and earth, software and campaigns before hardware — with motor B's usual geography: on rear-motor cars this inverter may live at the back with its own coolant run and its own supply wiring, all of it in underfloor weather.
Likely causes
Start here
- Faulty inverter coolant pump · moderate
- Failed power or earth supply to the module · moderate
Less common
- Road damage to underfloor wiring · moderate
- Faulty power inverter · specialist
Symptoms
Components involved
Information, not instruction
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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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