Code Definition

P0A78 (266) — Drive motor A inverter performance

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Toyota

About P0A78

P0A78 is a generic (obd-ii standard) powertrain diagnostic trouble code recorded for Toyota vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0A78 is stored, the module has detected a plausibility fault — the measured value is in the electrical range but is not consistent with expected operating behaviour.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0A78 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

On this Toyota hybrid the inverter for Drive Motor A converts high voltage DC from the hybrid battery into three phase AC for the motor, and the MG ECU continuously monitors its output voltage, current balance, switching operation, and feedback signals. DTC P0A78 sets when the MG ECU detects abnormal performance or an internal malfunction in this inverter that is not traced to a specific motor or sensor fault. Common causes include an internal inverter or IGBT fault, overheating from a cooling system problem, a three phase output imbalance, a weak high voltage supply, or a degraded DC link. Wh...

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