Adventures in inverter coolant pump repair

I’m posting my experience replacing my inverter coolant pump with the hopes that someone might find it helpful if they are faced with a similar situation.

I was 110 miles into a 120 mile trip, going 65 mph on the expressway in my 2006 Prius when my dashboard lit up like I hit a jackpot in Vegas. I had the red triangle of death along with a check engine light and others. Since I was almost home I took a chance and drove the rest of the way and arrived home without a problem. I hooked up my OBD II code reader and saw I had a P0A93 code which indicates a failure of the inverter coolant pump. I looked into the coolant reservoir and the surface of the coolant was perfectly smooth, so the pump was not working. My Prius has 187,000+ miles and the pump, known to be a common point of failure, had never been replaced.

I went on Amazon to order a replacement pump. The part number I looked for was a G9020-47031. While searching for the part I noticed another part designated as 04000-32528 which appeared to be identical (and at $65 vs. $85). The description of the pump indicated it was a “Genuine Toyota part." When it arrived, it seemed identical to the one in my car and came in a Toyota box. Interestingly, the Amazon vendor I purchased the part from sells both part numbers and the in the photos, the parts appear identical except for the price. If it was a counterfeit, at least it was a good one.

I decided to attempt the pump replacement by unbolting the inverter as shown in a Luscious Garage YouTube video. I unbolted the two inverter brackets near the front of the car and found I could shift the inverter slightly to the left (but not quite as much as in the video.) In the video, the mechanic seemed to loosen something near the firewall, but because of the camera angle and speed, it was impossible to see exactly what she was doing. I found I couldn’t quite undo the three bolts holding the old pump because of interference from the frame and headlight connectors. I was also having trouble unlatching the pump electrical connector, so I decided to switch strategies and remove the headlight to gain better access.

There are three bolts holding the headlight. Two are under the hood and easy to reach, but the third is on the side of the car behind the wrap around part of the bumper. I undid the fender skirt and the bolts holding the driver’s side of the bumper and took out the third bolt. Once the headlight was removed, there was plenty of room. I left the old pump bracket in place, unbolted the pump from the bracket and unplugged the electrical connector. I didn’t want to drain/bleed the coolant, so I clamped each hose using two pieces of scrap wood which I pressed together with “C” clamps. Not as convenient as using radiator hose clamps, but it did the job.

With the hoses clamped, I broke the hoses free from the old pump and moved the hoses to the new pump (losing only a small amount of coolant.) With the hoses in place, I bolted the new pump onto the old bracket and hooked up the electrical connector. I turned on the car to check the new pump and . . . nothing. The pump did not run. I bench tested the old pump and it ran fine. I plugged the old pump into the car and like the new pump, the old pump did not run.

Next, I pulled out the wiring diagram. I checked the 15 Amp AM2 fuse which feeds the pump and it’s good. +12 Volts feeds through the driver side J/B assembly behind the dash and I skip trying to check the INV W/P relay for now. I get my multimeter out and check the two wires feeding the pump. Pin 2 which is the black wire has +12 Volts with the car running (IG-ON). Pin 1, white with a black stripe, is supposed to be connected to ground, but is instead open circuit with no connection to ground. I check the wiring diagram and pin 1 is supposed to be connected to the “EE” ground which terminates at the “left side of the suspension tower”.

I start inspecting the white/black ground wire and as I get towards the firewall, I see a 2-pin connector near the suspension tower which is literally chewed up with the single wire going into it separated from the connector. Darn squirrels! I test the wire and find that it is, in fact, the ground connection for the pump. The wire is separated right at the connector, so to reconnect it, I would have to get the pin out the connector. I don’t have a pin removal tool, so I decide to cut off the mating half of the connector and directly solder the two wires together.

I check the pump and it’s working. Phew! I’m philosophical about replacing a working pump and tell myself it was probably going to fail soon anyway.