I've noticed that each summer a reasonable number of posters report inverter coolant pump failures. As a result I've recommended that owners consider replacing that pump no later than at 100K miles as a preventive measure. Taking my own advice, I decided to replace that pump on my 2004 with 81K miles since we are about to move to the very hot southern Arizona area. I'm not interested in having that pump fail in 110 degree F weather, resulting in a potential life-threatening emergency if we are stuck in the desert. I would rate the pump replacement as an intermediate level DIY project. It is not very easy because access to the pump is tight. You can see the pump if you open the hood and look behind the driver's side headlight assembly. What you will need: - G9020-47031 MSRP $116, Net $88 for weborders at Champion Toyota, Houston - One gallon of Toyota Super Long Life Coolant. You'll end up using 3 quarts or so. - 10 mm and 12 mm sockets, a good socket wrench and extensions. I found a U-joint was helpful as well as box wrenches in those sizes. You will need a 14 mm open end wrench and a 10 mm box wrench when opening the inverter coolant bleed valve. 24 mm (or 15/16") socket for the transaxle coolant drain plug. - Drain pan for old coolant The Toyota repair manual suggests removing both engine under covers to start. There is no reason to remove the RH under cover and the LH under cover doesn't provide much additional access. Hence I did the job working through the hood opening, except when draining the old coolant. Start by making the Prius IG-ON (not READY) and listen to the sound of the old inverter coolant pump, so that you have an idea of where you need to end up when you are done. You should see turbulence in the inverter coolant container and you should not hear air bubbling in the fluid. Then make the Prius IG-OFF. Drain the inverter/transaxle coolant by removing the 24 mm hex drain plug at the bottom of the transaxle. Do not confuse with the transaxle ATF fluid drain plug which requires a 10 mm hex key socket to remove. After the old coolant has been drained, tighten the drain plug to 29 ft.-lb. Remove the black plastic cover over the radiator. Then remove a nut and a bolt that secures a bracket for a water valve located near the pump. The reason that you have to remove the valve is because that bracket is mounted on the same stud, and located on top of the bracket for the inverter coolant pump. Then remove the bolt that secures the back end of the pump. Disconnect the wiring harness connector. You will need to squeeze the tab on the connector to release it. This is not easy to do. Remove the two hoses. Note which hose goes to which part of the pump. This is not too easy; I ended up using a flat-blade screwdriver to insert between the hoses and the pump inlet pipe and outlet pipe in order to break up the seal that had formed. Remove the pump from the car. There is barely enough room to lift the pump up between the radiator hose and the inverter. Note that the inverter cover has a couple of curves in the leading edge. The curve closest to the LH fender is where I positioned the top spout of the pump while removing it. Installation of the new pump is the reverse of the removal process. Tightening torque of the hardware is 62 in.-lb. The bolt at the rear of the pump, although needing a 12 mm socket, does not require greater torque since it is also holding down the plastic relay/fuse box. Fill the coolant reservoir with SLLC, using a plastic funnel to avoid spills. Keep filling until the fluid level stabilizes at the FULL mark. Make the car IG-ON for 20 seconds. As the fluid level drops, replenish to keep the fluid at FULL. Then make the car IG-OFF. Open the bleed valve until you see fluid appear, then close. Repeat the steps in this paragraph until the sound of the pump quiets down, you don't hear air in the system, you see turbulence in the inverter coolant reservoir, and the fluid level no longer drops below FULL. Take a test drive for a couple of blocks. Then check the fluid level when the car is IG-OFF. Top off as needed so the fluid level is at the FULL mark, make sure the bleed valve is tight, replace the radiator cover, and you are done. The old antifreeze is poisonous and very harmful to local fauna, pets etc. so please dispose of it responsibly. The first two photos show the inverter coolant pump outlet hose (forming a reverse S shape) in the middle, and the mounting hardware for the valve bracket immediately to the left and the right of that hose. You can see this is not easy to get to. The next photo shows the new pump and its part number. The next photo is blurry and underexposed unfortunately, but shows the location of the old pump. Note that it is in front of the main relay/fuse box (you can see the leading edge of the relay/fuse box where you depress the catch to release the cover) and behind the LH headlamp. The final photo shows the new and old pumps side by side. A curious note: I used my Fluke DMM to measure the resistance across the two terminals of the old pump which was still operational. The resistance value was around 1.5 M ohms. When I reversed the ohmmeter leads I got a negative value, so it appears that the pump has more to it than just a simple DC motor - looks like at least an inline diode and a capacitor are involved, who knows what else. I did not measure the resistance of the new pump.