NOTE: Inverter pump replacement is covered by Toyota for model years 2004-2007, until November 30th, 2013. For more info, see the dedicated blog:
All hybrids have “inverters”—assemblies that translate high voltage direct current (DC) of the battery into alternating current (AC) for the motor/generator(s). The chopping and reconstituting of current creates heat, which must be dissipated for the components to last. Honda hybrids are relatively light duty and can get by cooling the inverter with air, tucking it back near the trunk alongside the battery. Toyota “hybrid synergy drive” style hybrids are heavier duty and require water-cooled inverters, which is why they are located under the hood (for proximity to the radiator).
On the water-cooled varieties, the “inverter water pump” circulates the coolant from the inverter to the radiator whenever the car is on. Circulation is confirmed by removing the cap on the inverter coolant reservoir and checking for turbulence (see video below). If turbulence is missing, one of the following is true:
1.) The inverter water pump has failed
2.) The pump circuit is open (no power e.g.)
3.) The cooling system is blocked (kinked hose, e.g.)
4.) The cooling system has an air pocket
Regardless of the reason, the lack of circulation will cause the inverter to overheat, setting a trouble code. On the second generation Prius (model year 2004-2009) that code is P0A93, information subcode 346: “Inverter Cooling System Performance.” Diagnosis commonly leads to a seized water pump, a problem we’ve seen multiple times on Prius as young as 55,000 miles.
Toyota has updated the design of the replacement pump (part number G9020-47031) to solve the problem. You can tell the updated design from the original by the color of the mounting base (black is original, silver is updated) though late models with the updated design (silver base) have also experienced failures. Toyota has also issued a Technical Service Bulletin outlining the failure on 2004, 2005, and 2006 Prius: TSB EG001-07.
The pump can be replaced from above in just over an hour (LG bills 75 minutes), with a cost breakdown as follows:
Toyota Inverter Water Pump G9020-47031 = $138.86
Quart of Super Long Life Coolant = $5
Sales Tax = $13.67
1.25 Hours Labor = $150
Total = $307.53