Motor-generador defectuoso

The electric machine that both drives the vehicle and generates from it, and on a hybrid it is also the starter — which is the fact that makes its failures read so strangely. A code saying the engine failed to start on a hybrid is very often not a starting-system fault at all, because there is no conventional starter to be at fault; the traction machine cranks the engine.

Its faults split into electrical and mechanical and the codes reflect that. A winding or insulation failure usually presents through the inverter and the high voltage system, so battery voltage and current codes appear alongside it. A mechanical performance code is the machine's rotor, bearings or coupling — it turns, but not with the torque or at the speed commanded.

What it is most often blamed for is a weak battery. A machine cannot deliver torque the pack cannot supply, so a degraded pack, a cold-soaked one, or a state of charge that has fallen too low produces exactly the symptoms of a failing motor generator: slow or failed cranking, poor assist, warnings under load. Establish that the pack can deliver current before condemning the machine, because it is among the most expensive parts on the vehicle and the pack is the commoner fault.