When working on the Prius brakes the important thing is to disconnect the 12 volt battery and if you wish to be super safe remove the two light blue relays in the fuse box under the hood. Failure to do at least one of these or both can lead to the pistons being ejected from the wheel cylinders. John (Britprius)
Have done many rear brakes without touching any relays or the 12v battery.. The front brakes I do take out the two blue relays only.
There have been a number of reports here on PC of rear pistons being ejected, and noted on my own car (UK version with rear discs) after changing the pads and refitting the relays, and connecting the battery an audible clang as the pads hit the discs, it not being possible to push them up to the discs with the brake pedal, as is possible with the fronts. This procedure is also called for in the manual. John (Britprius)
I ONLY work on 04 to 09 Prius and have NEVER had any brake errors. Ive done 5 or 6 rear brake jobs. I've probably been lucky. Maybe I should start taking the relays out.
The hydraulic circuit is identical. There may be times when you can get away with it, but from what I can make out if the hydraulic boost pump starts (low pressure or opening the drivers door can start this) pressure is applied to the front and rear brakes and a hydraulic integrity check carried out the reason codes can be issued by the brake ECU. Again per the manual. John (Britprius)