Inverter Coolant Pump

Master warning light (others too)?

A/C starts blowing warm?

Car shuts down after one or both of the above?

None of the above, but the car abruptly dies and shows little or no sign of life (mostly only headlights and dome lights) and won’t start (more on this towards the end)?

It’s probably your Inverter Coolant Pump, DTC P0A93.

One of the most common failures with the generation 2 Prius is the Inverter coolant pump. Unfortunately, the design is one of the few weak points. The pump runs full time all the time even if it’s not needed, and they just wear out. A Gen 2 will typically go through 2-3 pumps in their lifetime, and that’s AFTER the redesign and recall in 2007.

You can check for proper pump operation via the following video (read the video description for details):

If you don’t see the same vigorous flow as shown in the video, your pump has likely failed.

The car has no direct means of telling when the pump has failed. It only detects that the inverter is getting hotter than it should. It illuminates the warning lights and throws the code. Eventually, the safety systems disable various electrical systems as the Inverter heats up. First to go is typically the A/C (it’s all-electric and runs through the inverter) followed by the inverter shutting down altogether (car shuts off).

If the car sits overnight and cools off, things may be fine the next day… until the inverter heats up more than it should.

We don’t replace them anymore, but we recommend a shop in Tempe that does it for a VERY reasonable price, and they can generally get to you pretty quickly (they charge hundreds less than the dealer, and they only use genuine Toyota parts. Many shops will use Chinese knock-offs that cost half as much, and they pocket the difference).

Okay, so now we’re going to talk about the car being completely dead. If this doesn’t apply to you, then you can stop reading. Shorts seem to happen about 1 in 10 times. This occurs when the pump actually shorts out and blows the AM2 fuse that controls many critical systems. The AM2 fuse is 2nd down from the top right - blue 15A fuse. It is usually visibly bad, but it’s sometimes hard to tell. Check continuity to confirm.

You can also usually confirm this has occurred by placing your nose in the opening between the fuse box and the back of of the driver’s side headlamp. Sniff, and you will typically smell a “burnt electronics” smell. Here’s an image to assist:


AM2 fuse circled in green, and area circled in Red is where you would smell burnt electronics.

In this case, you have three options:

  1. Replace the fuse with a spare and hope the pump has gone open circuit. If the fuse blows again, you must unplug the pump to keep it from blowing the fuse every time.

  2. Unplug the inverter coolant pump - VERY hard to do unless you’ve done it before, but it can be done by hand. Replace the fuse, and you should be good to drive short distances.

  3. Tow it. They won’t be able to get it into neutral.

Driving without a functioning inverter coolant pump is NOT recommended except to drive to the shop. Do not use A/C or ANY other electrical devices. Best if it can be driven to the shop first thing in the morning after cooling overnight.

Good luck!