First gen brake issues

This is partially a follow-up to my last post. I've gotten my '03 Prius running and driving now and it's been great the last few days. The issue turned out to be the inverter (including my first replacement one), and then I pulled, replaced a few modules, balanced, and reinstalled the HV battery. That has all worked great. I was poking around with the aftermarket radio and interior controls that didn't function. This is when I put my foot on the brake with the car off to put the car into "B" so that I could fully remove the center trim piece (which didn't shatter, fortunately). The pedal basically went to the floor with little pressure. I thought that was odd, but didn't want to worry about it until I had to since I know that these Prius brakes are weird.

Anyhow, the next time that I went to start the car (which was just a few minutes later to test the radio and such, which I fixed), the brake pedal goes to the floor with little resistance and will build a bit of pressure with pumping the pedal but does not hold that pressure. The ABS and BRAKE lights are also on, and the red triangle shows up and the car screams at me when the car is put into gear. I can hear the accumulator pump thing running occasionally but it doesn't seem to really be doing anything like it usually does. I attempted to use my Veepeak bluetooth scanner with the Torque Pro app and that did not read any codes. What do I need to do to diagnose further? I'd love to have this car driving as the MFD tracked 52-53 MPG on average over the last couple of days. Other than this brake stuff the car drives and runs great now.

 

I also forgot to mention that I had disconnected the 12v battery to unplug the radio things, and this happened when I attempted to start the car after I reconnected the 12v. That being said, I have also disconnected the 12v before and not had any issue like this.

 

Nevermind, tried bleeding the brakes and that just worked. Funny how that is. I guess the $500 Prius lives with no issues whatsoever. Suspension looks great, and tires are even in good condition. It'll need front pads soon-ish but it is a hybrid so they'll last considerably longer.