2004 Prius cold weather brake problem

Although this may not be the cause, are you still on your original 12 volt? If yes, it's definitely at end of life now.

Please run the test at Weird stuff happening? MPGs dropping? Test The Battery | PriusChat after the car has sat MANY hours or overnight. Please tell us the 3 values (not just 1). Don't go changing the battery first until you tell us the values...

If you have HIDs, you can avoid unnecessary cycles on the lights by toggling between off and parking light positions.

Weird stuff can start happening w/a low or bad 12 volt. Don't waste $ on having a dealer "test" the 12 volt (07 Prius Dead - Any Guesses? | PriusChat).

What do you mean by "all of the brake indicators go on"? Are you talking about warning lights? Which ones? Any message on the MFD? My 1st wild nice person guess would be a bad brake actuator, but that would suck as it's really expensive to replace. I'll let the repair experts (not me) chime in.

If you finally get to the bottom of this w/an actual correct fix, it might be worth filing a safety complaint at Home | Safercar -- National Highway Traffic Safety Administration (NHTSA).

 

This is very strange. If any brake warning lights are on <such as ABS, VSC, and/or ((!))> then the skid control ECU is supposed to log the appropriate DTC and retain the fault codes even if 12V battery power is lost. Perhaps the problem is with the skid control ECU itself.

I suggest the next time this happens during business hours, that you make every effort to immediately proceed to your local Toyota dealer, show the service writer the warning lights, and ask that the DTC be immediately read by a tech to ensure they are not lost when the car is powered down.