Brake Booster Malfunction

But only if the VIN data used on the parts site is better than the VIN data on the Toyota Owners website.

The Toyota Owners website reports my 2010 IV (with 15" wheels from the factory) as being a 2010 V (which would have had the 17" wheels).

 

Is it usually the (lower) pump assembly that goes bad?

 

In my understanding, no.

The pump is the thing you hear when either one goes bad. If there is any fault anywhere in the system that requires the pressure to be frequently replenished, then you hear the pump doing that.

There are two completely different kinds of fault that can lead to that behavior.

In one, some valve loses its ability to completely seal, so pressure bleeds off through it, and the pump has to run to replenish it. There are only a couple valves in the pump/accumulator assembly (and one of them never even opens in normal operation, so has no reason to wear out), while there are a dozen in the master cylinder/actuator/booster assembly and they get used lots. So the odds for this issue are on the box with all the valves in it.

The other, completely different, issue is when the accumulator bellows develops a crack and some of the nitrogen gas leaks out. That also leads to frequent pump running, for a different reason. (With less nitrogen, the volume of fluid between the cut-in pressure and the cut-out pressure becomes lower, just like in a house with well water and not enough air in the pressure tank.)

That second issue is always the accumulator, when it happens; it just doesn't seem to happen as often as the hydraulic leak issue. There was a 2010 batch of accumulators built with a defect that made them crack early, but outside of that batch, it seems to be unlikely until late in old age.

There is an observable difference between the two different causes. The hydraulic-leak issue, once it gets bad enough, can result in the pump having to continually cycle even while nobody is using the brakes. The lost-nitrogen issue does make the pump have to run more often, but still somebody has to work the brakes to use up pressure; it won't just sit there bleeding off and repumping itself with no use of the brakes, the way the hydraulic-leak issue can.

 

Thanks @ChapmanF . I copy/paste the info you posted, and link to location. This stuff is Byzantine.

 

I would email McGeorge and ask them. The 04002-33347 part is more expensive and, as you say, 47050-47140 comes up when you drill down the menus. The odd thing is when you search specifically for 04002-33347 it comes up as acceptable for a gen2 2008 as well as your gen3 2010. That makes no sense if it is the right part. Not so for the 2010 47050-47140.

 

Email them from their online parts website and ask what is the right part and what makes the difference. Inquiring minds want to know.

 

Entering the VIN still allows one to pick either either variant of the ABS assembly(*140 or *150)—both are shown to be compatible. I'm just wondering why the stock wheel size would be more relevant than that of the wheels currently on the vehicle. Are there any other differences in the drivetrain or braking system between a Prius V/5 and the lower trims besides the wheel size and ABS/actuator assembly?

My initial thoughts would be that the ABS module needs to calculate the slip ratio to maximize brake force, and to do that it needs to know the effective radius of the tire. Although this is something that could just be programmed in after installation, perhaps the two variants are pre-programmed differently for different tire sizes? If so, shouldn't it be the current tire size that would matter rather than the stock size?

 

KBeee - I went with Hometown Hybrids who gave me a 12 month 25K mile warranty. Dropped it off Thursday night after they were closed and it was ready today around 1PM. $1900 compared to $3000 or more at the dealer.

 

Good point. If there is no noticeable drop in reservoir fluid level over time, the leak is internal. Then:
Pump cycling continuously without brake use ⇒ Hydraulic leak in actuator assembly
Pump cycling continuously without brake use AND accumulator occasionally "whistling" between successive operations ⇒ Hydraulic leak AND nitrogen leak in accumulator
$5 mechanic's stethoscope can confirm both conditions.

 

Just sharing for people that may want to buy used Prius. Old and updated brake booster pump pictures.

It is a safety issue, it is possible that Toyota will do recall again or campaign even the first one expired in 2021 August. Just like the inverter campaign, they extend it to 15 years/unlimited miles after many complaints. USA and CANADA sold more Prius than any other hybrid in the rest of the world. In USA, most Prius owner drive their cars beyond 150k miles. There is still possibility of a new campaign, so keep the receipt and records from your mechanics. Don't over optimistic but keeping receipt is always good.

 

That's what I'm thinking. It's not the wheel size specifically; it's that models with the 17" wheels have other differences.

The 15" and 17" tires are very close in diameter.

 

It would be interesting to know what these differences are—they might provide some clues about the difference between the two actuator assemblies.

 

With our 2010 Touring (CDN model, similar to US level 5, aka V for 2010 IIRC) I've heard there are suspension differences. In the specs: turning radius is larger, and steering wheel lock-to-lock is reduced. Subjectively: we drove a 15" wheel level tester first, then a few days later the Touring. I felt a lot more comfortable in the latter; it felt more planted, sure-footed somehow.

 

I would be willing to bet there's no physical difference between the actuator assemblies, but they come factory flashed with different firmware calibrations corresponding to the different dynamics of the cars.