Gen1 Prius DTC 3125 & 3130

Once the car has cooled down, see if you can drive it (around the block in your neighborhood, for example.) If you can, then the inverter should be OK.

 

The inverter coolant pump may indeed be at fault. However, if you have P3130 with info code 346, and P3125 with info code 264, you may want to read TSB EG023-07, which identifies the inverter itself as the root cause of the issue if it occurs during heavy stop-and-go traffic and/or ambient temperatures above 90ºF. A redesigned inverter cures the issue.

NOTE: if the info codes are not those described above, the TSB does not apply.

Keep in mind that the coolant pump itself can fail intermittently. This can make diagnosis difficult. The pump has also been redesigned for improved reliability.

That is sort of true, and sort of not true. If the vehicle starts and runs normally after the system has cooled, the inverter is probably not damaged at that point. However, it may still become damaged.

See below.

If the problem is a lack of coolant flow, there is a very real chance of future damage. Patrick Wong's advice - to assume that the inverter is OK if the vehicle starts and runs after it has cooled down - may lead you to believe that the vehicle can now be safely driven. This is not necessarily so.

You'll want to first (1) confirm correct coolant level at the inverter's plastic expansion tank, near the firewall, as well as (2) confirm plainly visible flow (Toyota calls it "turbulence") when you remove the tank's cap and peer down into the tank itself. You may need a flashlight to get a good look, and the ignition key must be turned to the RUN position to power up the pump. If the engine is off, you may hear the whir of the pump running.

Drive without checking this, and yes, you may damage the inverter.

 

Then there must be another reason why the inverter coolant pump was diagnosed as the root cause of the problem.

Yes, it's possible.

Yes. At the very least, you may want to advise the service manager of the potential relevance of TSB EG023-07, and let him know that your vehicle was experiencing ambient temperatures above 90ºF, which is consistent with the conditions described in the TSB.

The time to ask that is before agreeing to the repair. Ask now, if you haven't already.

If you have signed an agreement to do so, and the car is not yet apart, you are liable for the retail price of the pump. However, if the inverter is not at fault, the pump is the most likely root cause.

Please note that this is not a diagnosis. It's common for folks on many forums to claim that a part is at fault simply because it commonly fails. If that part does turn out to be at fault, they then claim that they "diagnosed" the vehicle, when in fact they were making an educated guess with someone else's money.