Mushy brake pedal.

It sounds to me like either there is air in the brake system or the fluid is low. Or both. In any car, it should not be mushy.

 

Mine doesn’t feel extremely firm but it doesn’t seem to be mushy as you describe yours.

Do you know when brake fluid was replaced last? It’s required every 2 years according to my manual.


iPhone ?

 

My guess would be a previous brake fluid replacement that allowed some air into the system. Video #18 here by @NutzAboutBolts :

Nutz About Bolts Prius Maintenance Videos | PriusChat

outlines a brake fluid replacement on regular 3rd gen Prius. I'm not sure how applicable that'd be to your car, but hopefully would help. Try the "invalid mode" procedure for example, see if it works on your vehicle. A few comments on the video:

1. Motorized vacuum source, while handy, is not mandatory. I managed with just a syringe for basting fluid out of the reservoir, and for everything else just relied on someone pushing the brake pedal. I used a tube with a proper brake bolt nipple connector, and a large plastic jar with lid (hole drilled in lid for the tube). Cheap and simple.

2. At least according to the Repair Manual for 3rd gen Prius, the recommended order was Front/Right, Front/Left, Rear/Left, and Rear/Right.

3. I purchased and used two pints of Toyota DOT3 fluid, and that worked well. Per the video, I started out by basting out and refilling the reservoir with clean fluid, then did maybe 100~150 cc on each of the fronts, and the remainder on the rears. I checked the level in reservoir at the beginning, and set it at the same level at the end, holding a little of the new brake fluid in reserve, monitored the level over the next few days. Eventually I just recycled that reserve with the used stuff, since it doesn't store well.

The video is very well done, with split-screen showing how to open/close the bleed bolt, in conjunction with the pressing of the brake pedal, in particular with the front brakes. Following this, I think you'll expel air in the lines, end up with firmer brake. If not, maybe you have air back at the master cylinder, and then it might be time to get a Toyota service department involved.