Brake booster pump runs every 15-30 seconds

Hi everyone,

I'm new to this forum because frankly this is the first problem I have had with my wife's Prius. It's a 2012 Prius Two with about 130k miles on it. We have other cars, so downtime is not an issue, but we would like to fix this problem and keep her car on the road for several reasons. The big reason is that this car allows my wife to use the HOV lane to get to work, and she parks at work in a small parking garage that fits this car perfectly.

I was driving her car the other day and noticed a whirring sound coming from the driver's side dashboard every 30 seconds or so. More often when using the brakes. Some research on this forum pointed me in the direction of the brake booster pump. There was a very helpful post by mr_guy_mann here: whirring noise, both while running and after stopping | PriusChat

Using the Autel Maxi AP200 scan tool I confirmed the problem. The accumulator sensor pressure sensor voltage rapidly drops from 3.6V to 3.2V, at which point the pump kicks in, and this happens every 15-30 seconds. So, the issue is leaking valves.

Now that I know the problem, what I don't know is what I need to replace. The consensus is that I need to replace the complete ABS hydraulic assembly (pump, accumulator, and valves). Problem is, I can't find the part number for that entire unit. I found the brake booster assembly, and I found the pump assembly. The pump works fine and sounds fine. Can someone please point me in the right direction for the part or parts that I need? I understand that it's not cheap, but I don't want to buy used parts. If they are rebuildable, I can try, if it's worth it, but I'm guessing probably not. I do plan on doing it myself, I understand the bleeding procedure is very involved, but the Maxi AP200 has the software built in to do that. I am not a mechanic, but this is more of a hobby for me. I have rebuilt manual transmissions in the past. And like I said, I don't care about downtime for the car, we have other cars, so I can take my time waiting for parts. Thank you everyone for your help.

 

Thank you for your reply. Do we see ourselves driving this car for 10 more years? Hard to say. It's purely a cheap commuter beater for the wife, but her commute is about 70 miles round trip, 5 to 6 days per week. So I do need it to be reliable. But the car has literally zero other problems, so I think it's worth keeping it going for now. If I can find a good used part with a warranty, I would absolutely consider it. But I don't want to start scouring junk yards to pull parts from. Do you know the actual part that I need? Is it the brake booster assembly?

 

Perfect, thank you. I forgot about the mechanics stethoscope, that sounds like a great idea. Also, I wanted to make sure there wasn't something else I may have missed, so that narrows it down to the two units. Question then becomes, should I just replace both, as the pump is also a known failure point. Would really suck to replace the booster, only to have to do everything all over again because the pump fails in six months. I'm actually now leaning towards just doing them both. But the important thing for me was also to know that there isn't a third part or assembly that I am missing.

Any thoughts on whether I should replace a likely still good pump. It'll save about $600, but I'd rather do this only once.