Code Definition

P0A78 (284) — 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

This DTC sets when the hybrid vehicle control ECU detects abnormal performance of the Drive Motor A (MG2) inverter, based on internal monitoring of voltage, current, and thermal behaviour. Subcode 284 points to a fault where the inverter fails to drive the motor as commanded, due to internal degradation, thermal protection, or control circuit malfunction. The ECU sets the fault when the inverter’s output deviates significantly from the expected operating range under load.

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