Code Definition

P0A78 (505) — 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 Drive Motor A inverter runs self checks, energises its phases, and activates its control signals as part of the startup sequence at system power up. DTC P0A78 with this sub code sets when the MG ECU detects that the inverter fails to initialise or output the expected parameters within the specified time frame during that startup. Common causes include a startup circuit or timing fault, faulty power electronics preventing phase activation, an unstable control supply, a high voltage supply or precharge problem, or a control activation fault. When the inverter does not i...

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

Quick Facts