Coolant Temperature Sensor Location?

If you don't get any helpful info here, I'd recommend you try following the coolant hoses using the info you already found about the regular Prius location. If that doesn't help than there is always a 2 day $25 subscript to the repair manual which will include detailed instructions on how to actually install the part.

 

P0117 is a "low" input from the coolant temperature sensor, and Toyota uses negative-temperature-coefficient thermistors (the resistance goes lower when the coolant gets hotter) for these sensors—so a "low" input from the sensor corresponds to very hot coolant (or could also mean damage to the sensor wires so they touch each other and short). A wiring problem is more likely than the sensor itself going bad, something I've never seen happen, but there's a test if you want to be sure.



Because your overheat warning light ("hey the coolant reads hot") flashes at times of high load on the freeway (when hot coolant could be believable), and the P0117 code ("hey the coolant reads off-the-scale hot") can also mean just what it says, I think the first order of business is to make very sure your engine is not really overheating at those times.

If you're sure it's not really overheating, then you can proceed with whether the sensor or (more likely) wiring might be bad.

But I would start with what the coolant level is (in the bottle and in the radiator neck). With an OBD-II scan tool you can watch the temperature reading as you drive. If the reading matches the weather when the car has been sitting before you start it, and if the reading increases steadily as the engine warms up, and on the freeway keeps rising to where the warning light flashes, I would say the sensor is doing its job just fine and you shouldn't shoot the messenger just because it's telling you the engine's too hot.

On the other hand, if you see the reading not match the weather when the engine is cold, or you see the reading bouncing weirdly or flakily like it isn't really tracking the coolant temperature, that could be more of a sign of a sensor or wiring issue.

 

We have this page that explains a number of different ways to access the manual. Some may be no cost to you, if a public library near you participates, etc.

Toyota Service Information and Where To Find It | PriusChat