Code Definition

P0A78 (305) — 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 fail signal is expected to follow predefined logic states under normal and faulted conditions to report inverter protection events to the MG ECU. DTC P0A78 with this sub code sets when the MG ECU detects a logical conflict or invalid signal pattern, with the fail signal sitting in an unexpected state, showing erratic transitions, or contradicting the actual inverter status. This usually indicates a logic fault in the fail signal output, a wiring short or open, a connector problem, or noise and crosstalk corrupting the line, rather than a genuine...

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