Code Definition

P0A78 (285) — Drive motor A inverter fail signal indicates overheating

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.

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 receives a fail signal indicating an over-temperature condition within the Drive Motor A (MG2) inverter. Subcode 285 specifically denotes that the inverter’s internal thermal sensors have detected a temperature above the calibrated threshold, prompting a protective fail signal to be sent to the ECU. This may occur due to excessive load, cooling failure, or internal inverter degradation.

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