P0A78 on Toyota
Drive Motor A Inverter Over-Temperature
P0A78 on Toyota vehicles indicates drive motor a inverter over-temperature. Au7o has documented this code across 1 Toyota model — most commonly on Prius C. P0A78 is a hybrid/electric-vehicle code indicating that drive motor 'A' inverter has overheated. The inverter converts the high-voltage battery's DC power into AC to drive the electric traction motor, and it has temperature sensors; when the inverter temperature exceeds safe limits, the control module sets this code and usually reduces power to protect the components. Symptoms include reduced power (limp mode), warning lights, or in severe cases the vehicle refusing to drive. It points to an inverter cooling or electronics problem in the high-voltage drive system rather than the gasoline engine. Typical repair costs on Toyota range from $200 to $600, depending on the specific model and root cause.
Common Causes of P0A78
- •Low coolant or air in the inverter cooling loop
- •Failed inverter/electronics coolant pump
- •Clogged or restricted inverter cooling passages/radiator
- •Faulty inverter temperature sensor
- •Failed or degrading inverter/power module
- •Cooling fan or thermostat fault in the inverter loop
- •Excessive load or related high-voltage system fault
P0A78 on Toyota by Model
Toyota Prius C(1 issue)
- Inverter Coolant Pump Failure and Hybrid System Overheat2012-2019
The Prius C has a separate cooling circuit for the power electronics (inverter/converter). The electric pump that circulates coolant through this circuit can fail, causing the inverter to overheat. When the inverter overheats, the hybrid system enters a protective shutdown mode, displaying "Hybrid System Malfunction" and severely limiting power output. The pump failure is often caused by coolant contamination or bearing wear.
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View P0A78 across all makes →Frequently Asked Questions
What does P0A78 mean on Toyota?▼
P0A78 stands for "Drive Motor A Inverter Over-Temperature." P0A78 is a hybrid/electric-vehicle code indicating that drive motor 'A' inverter has overheated. The inverter converts the high-voltage battery's DC power into AC to drive the electric traction motor, and it has temperature sensors; when the inverter temperature exceeds safe limits, the control module sets this code and usually reduces power to protect the components. Symptoms include reduced power (limp mode), warning lights, or in severe cases the vehicle refusing to drive. It points to an inverter cooling or electronics problem in the high-voltage drive system rather than the gasoline engine. On Toyota specifically, this code is documented across 1 model.
What causes P0A78 on Toyota vehicles?▼
Common causes on Toyota: Low coolant or air in the inverter cooling loop, Failed inverter/electronics coolant pump, Clogged or restricted inverter cooling passages/radiator, Faulty inverter temperature sensor, Failed or degrading inverter/power module. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0A78 on a Toyota?▼
Repair costs on Toyota range from $200 to $600, depending on the specific model and root cause.
Which Toyota models have P0A78 documented?▼
Au7o has documented P0A78 on 1 Toyota model: Prius C.