Toyota Prius: ZVW50 Inverter Electric Water Pump Failure

The ZVW50 Prius (fourth generation) employs a dedicated brushless electric water pump to circulate coolant through the power control unit (PCU), which integrates the boost converter, MG1 inverter, and MG2 inverter into a single assembly. The pump's bearing and impeller are subject to wear from continuous low-speed operation and are known to fail between 80,000 and 150,000 km. Loss of PCU cooling triggers the inverter's thermal protection circuit, reducing available hybrid power immediately, and sustained loss of cooling without intervention can result in PCU damage costing several thousand dollars to rectify.

• Master warning triangle with 'Check Hybrid System' message on multi-information display
• Abrupt reduction to reduced-power mode, particularly after highway driving
• P0A93 or inverter over-temperature DTC logged in PCU ECU
• Inverter coolant reservoir found low without external leak

1. 1

   With ignition switched on, listen for the electric water pump audible hum from the engine bay — absence suggests pump failure.

2. 2

   Scan for P0A93 (inverter cooling system performance) or related PCU thermal DTCs.

3. 3

   Check coolant level in the dedicated inverter reservoir (separate from the engine circuit).

4. 4

   Inspect the pump electrical connector for corrosion or spread terminals.

Parts involved: Water pump.

≈A$410 to ≈A$870 at independent workshop rates, shown as an approximate guide in Australian dollars. That is for this job on its own, not for the car.

An estimate, converted to Australian dollars, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the inverter cooling system ever been serviced or the electric water pump replaced?”
• “Has a 'Check Hybrid System' warning ever appeared during ownership?”
• “Is the inverter coolant reservoir full and free of discolouration?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.