P261B code. Could I have damaged a water sensor if there is such a thing?

There are a couple water temperature sensors, but you're unlikely to have damaged them, and they aren't what a P261B code is about, anyway.

P261B means the electrically-powered engine water pump was doing less than 900 RPM when the engine control module wanted it to pump faster than that.

There's a plastic impeller in there that sometimes swells or splits and becomes harder to turn, slowing the pump down. It's possible having the wrong stuff in there might have accelerated that deterioration of the plastic, but it's also possible it just happened to be about that time for the water pump. You haven't mentioned the mileage on the car.

You might be used to cars that have a radiator filler and an overflow bottle. Your Gen 3 liftback doesn't. The bottle over by the inner fender isn't an overflow bottle, it's a "degas bottle" and it is the only filling location for the system.

You'll notice it has lines marked LOW , FULL, and B. B is above even FULL, and it is the line you use when burping the system. If the system has been drained, you fill it all the way to B, put the cap back on, start the engine, warm it up to full operating temperature and run it that way for several minutes, shaking various radiator hoses (while keeping your fingers out of the fans). Then you turn the engine off, wait for everything to cool, and notice the level has normally gone right down to FULL, just like the engineers knew exactly how much air would burp out.

You'll have another chance to practice that after replacing the water pump.

 

Seems like 90,000 is early for a water pump to poop out, but you could just be lucky, I guess.

Also seems like early-ish mileage for EGR cleaning ... it would be interesting to see your before-cleaning and after-cleaning EGR flow test results if you saved those.

 

People often work on their EGR systems and then report qualitative judgments of the condition like that.

For the PriusChat community, it is really useful to also report the EGR flow self-test numbers from before and after the work. Helps us kind of map out how common qualitative judgments at different mileages map out into actual flow.

Had you received a P0401 insufficient-flow code before doing the work?

 

P261B means the electrically-powered engine water pump was doing less than 900 RPM when the engine control module wanted it to pump faster than that.

The pump doesn't "send" the code. It has a tachometer output. The ECM reads that, and decides when to set the P261B code.

Techstream isn't needed to get EGR flow numbers. "Mode 6" monitor test results are a standard OBD-II feature.