Prius stalls/shutdown in hot weather

The first thing that occurred to me was the inverter coolant pump having failed or just maybe not working efficiently enough anymore. One thing is for sure if you are seeing many alert dash lights appear including the triangle alert, there are at least 3 or 4 ECUs that have codes just waiting for you to read. This will give you insight into what is causing your car concern. If you could tell us what those codes are, we can give you a direction on how to proceed.

 

All you need to do is open the inverter coolant reservoir and look inside with a flashlight. If the coolant is just sitting there and not moving with the car in Ready the pump is bad. If you continue you use it it will blow fuse AM2.

Its probably the most replaced part on this site besides the mysterious 12 volt battery.

If the pump has over 65,000 miles on it its suspect. Hundreds of posts on how to install a new pump using the Search Forums link up top.

You must use a factory pump. The pump you buy at a parts store is Chinese junk.

I like Olathe Toyota parts Online they do a good job and much cheaper than over the counter at the dealer. Last I looked a pump was $100.

Coolant for that system is the same as the ICE radiator Totoya factory LLC.

 

That is a big no no. The NiMH cells (all of them) self discharge significantly over that long a time period, and that can lead to the pack becoming unbalanced. It is often all downhill from there.

That said, the "fails on heat" behavior is characteristic of a bad inverter pump, much less so of a weak pack. Still, it might show up that way for a bad pack if you were running the A/C, which takes quite a bit of current, and could be enough to push it over the edge.

If you can get Techstream or Dr. Prius working, probably Torque too (but I'm not sure), you could read the module voltages and confirm or rule out a traction battery issue.