Code Definition

P0A78 (279) — 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 must switch all three phases in balance and on time to convert high voltage DC into smooth three phase AC for the motor. DTC P0A78 with this sub code sets when the MG ECU detects an abnormality in inverter phase output balance or timing, such as phase current distortion, voltage mismatch between phases, or delayed switching events that deviate from expected operation. Common causes include a weak or slow switching inverter leg, a degrading IGBT or gate driver, thermal stress, a poor high voltage phase connection, or an unstable supply. The E...

Join TaT to view the complete code information and diagnostic details.

Quick Facts