Toyota Prius C [Aqua] 2012 Brake Booster Assembly removed, pictures

Good work!

One clarification: if you have brake codes reported and the brake pump is running frequently, the original cause can be in either assembly. Both of them contain valves that could stick open, causing pressure loss. There are more of those valves in the booster assembly, so more chances for that one to be the culprit, but the facts on the ground can turn out to be either one. There is also a metal bellows in the pump/accumulator assembly that can fail, which is another way to cause much the same symptoms.

So the best way to avoid the expense of replacing both assemblies is to both (a) not go too long with a known problem before addressing it, and (b) make some effort to pin down which assembly has the problem. Some people report their pump is running every several seconds, and when the leakage is that bad, a mechanic's stethoscope can probably tell you which assembly is doing the leaking.

It's also worth the effort to read the brake diagnostic codes when those warning lights come on, and not just jump to conclusions because the lights are on. They can come on for a lot of reasons, and some of them won't require replacing any expensive parts at all.

It is probably possible in the c to read the brake codes without any special code reader whatever, just by using a jumper wire and counting some blinks. (I say 'probably' only because I don't know about the c for sure; it's definitely true in Gen 1 through the Gen 3 liftback, and the c system is very much like Gen 3.)

With a scan tool, especially with Techstream, it is also possible to watch various pressure readings inside the unit, test-actuate different valves, and so on, as part of tracking down a problem.

 

There aren't electronic ones like you find in the booster assembly, but there are a couple simple mechanical ones, a check and a relief. As I said, if it's a valve leaking the odds favor the booster assembly because there are a dozen valves in there and they operate so often, but the possibility of a problem originating in the pump/accumulator shouldn't be ignored, given the cost and annoyance factor of replacing the wrong thing.