Will not enter "Ready" mode, will enter ig on, no red triangle, can't pull any codes

So the past few months my wife's car has intermittently decided that it doesn't want to start, usually when it is very hot outside. But after a few minutes sometimes up to like 10 or 15 minutes of trying to start the car it would ready on and be fine. Until a couple days ago. My wife was at the doctor and when she went to leave the car would not start, she tried for about half an hour letting it sit with windows open, etc and trying again. Since this has been an issue it the past I thought I just needed to be more deliberate with the starting process to make sure the car recognizes all the steps so I do not need a tutorial in how to start a prius please skip that advice. The lights currently lit on the dash during ig-on are the check engine, vsc, abs, ((!)), and the squiggly line car, but mysteriously absent is the big triangle exclamation mark of doom.

Later that day I picked her up from her parents and swung by the car to try again to see what would happen, 90% sure it would just start up and we could leave, but with no luck. I tried unplugging the 12v battery for a few minutes and then plugging it back in, but still no luck. So the next day I came back with my tools and techstream computer. I checked the on board diagnostic screen activated by the headlights and it showed 11.8 volts on the 12v battery, checked with a multimeter and got 12v at the poles which makes sense with all the attempts to start the vehicle, but since I had driven my other prius over to work on hers I swapped 12 v batteries between the two hoping for an easy fix. Other car battery read 12.8v at the poles and when installed didn't change anything. From ig-on I attempted to scan the computer with techstream, but was unable to pull any codes as in the computer shows communication with ecus, but reads no trouble codes, and the engine ecu returned an incomplete scan message during the health check which I assume was due to the fact that I am unable to get the ICE running.

I also attempted to get it into test/maintenance mode so I could try to get info from the engine, but after doing the gas pedal + neutral +pedal + park + pedal dance all I was able to get was the display to show "problem" at the top of the screen the small red car with exclamation in the top left corner. and the engine was still not started, however after looking at that process again I realize that I didn't press the power button after "problem" showed up on the screen so I will have to try this again.

I took a test light and checked the fuses in the engine bay and was unable to find a blown fuse. I checked the main fusible link in the box and did not see any broken copper. I also swapped the positive pole connector that mounts to the 12v battery to make sure that wasn't an issue, as well as the relay box located next to the battery and got no result. My reasoning for checking these parts was due to the fact that we got a lot of rain here about a week ago and I discovered the battery well to be full of water up about half way on the battery. Same water issue happened in my other prius I just sealed the roof and no issues were had, but I don't know where to go from here. I am about to have it towed home, and I'm just frustrated that the car has run fine for us for over a year, and now decided to pretend to be broken. Also it has like 312000 or something miles or 326000, I don't remember which car has which.

Any advice on what to try or where to look next would be helpful, or if any more info from the car would help narrow it down I can get that too.

 

I appreciate the input, Ill check the brake pedal sensor, and see if I can pull some codes again. and if it ever cools down enough here in Florida, I hopefully can get the engine started again and do a full scan, but flying blind makes this very difficult. I did see that there was a fan related to the interior HV battery cooling vent located inside the car that can get clogged with hair and dust and cause some heat related problems as well, I think my next plan of attack will be to swap brake pedal sensors and see if that does anything and if not I'll pull the back seat apart and see about the fan.

 

I haven't had time to work on it and likely wont until this weekend, but I replaced the inverter pump last year with a unit from NAPA, and haven't had a problem with it since, plus there was never a code for it, the thing that is really throwing me off is the fact that my techstream won't communicate with the engine computer, but will with the rest of the car. maybe that computer has gone bad? Hopefully I'll know more this weekend.

 

Final update, I got the car running again, it was the brake light switch preventing the car from recognizing that the brake pedal had been pressed and because of that will not start. I switched the part from my working prius to my dead prius and it started right up. although I bench tested both switches for resistance in open and closed position and both switches seem to operate fine. I believe it may have been out of adjustment. I will reinstall the bad one into my previously working prius with proper adjustment and see if it functions correctly, but in hindsight I should have checked adjustment before I removed the part to swap. But the bottom line is I can't believe a bad brake light switch caused such a headache, I was talking about scrapping the car because I couldn't figure it out, kind of crazy.

 

addition to final update, I put the 'bad' switch in the working car and adjusted it properly, and both cars started just fine, so the culprit was definitively an out of adjustment brake light switch and it cost about $120 to tow the car home because of it.