Code Definition

P0A78 (283) — Drive motor A inverter fail signal circuit shorted

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 short-circuit (voltage pulled to ground or to supply) in the monitored circuit.

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 a short circuit condition in the fail signal line from the inverter for Drive Motor A (MG2). Subcode 283 specifically indicates a short to power or ground in the fail signal circuit between the inverter and the ECU. The fail signal is a dedicated line used by the inverter to report internal faults or protections. If the signal line is stuck at an unexpected voltage level or shorted, the ECU interprets this as a communication fault with the inverter.

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