Code Definition

P0A78 (286) — Drive motor A inverter fail signal circuit error

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 an electrical-circuit fault in the wiring, connector, or driver associated with the named component.

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 uses a dedicated fail signal line to report internal malfunctions or protection triggered shutdowns, such as overcurrent, overvoltage, or thermal faults, to the MG ECU. DTC P0A78 with this sub code sets when the MG ECU detects an error on that fail signal circuit, with the signal missing when expected, stuck high or low, or inconsistent with the inverter status. This usually indicates a circuit integrity problem such as an open, a short, or a connector fault, a faulty fail signal driver in the inverter, or a genuine inverter protection event bei...

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