Gen 2 C1256 low accumulator pressure -- help verify part numbers for fix?

In gen 2 I have not heard of much need to replace the master cylinder. The gen 2 M/C is conventional and very simple. Nearly all the interesting stuff is glommed together into the actuator assembly. (The stroke simulator is off someplace else, but I don't hear much about that needing attention either.)

 

You've quite possibly read a lot that was about gen 3. In gen 3 the master cylinder and the actuator and the booster and the brake ECU are a single assembly, while the booster pump (note that 'booster' and 'booster pump' are different things) and accumulator make up a different assembly, and both of those two assemblies can contribute when pressure isn't being held.

But if you're talking about a gen 2, the booster pump and accumulator and actuator are all combined in one assembly that is pretty much where most of what can go wrong is, and the master cylinder in gen 2 is a dead-simple conventional one—lacking even a booster—more like you'd find on a car of the '60s.

I'm not at all surprised that an AI would come up with some cockamamie result, given the number of significant differences between Prius generations that it would hardly know to keep apart in all the internet text it has ingested.

 

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You should order the 44510-47051 part if you have a Gen 2 car. This is a pretty expensive part, if you can wait on it, they often go on special for 25% off the dealer discount prices. The last one I bought I paid $917 with the discount

 

When you order it from the parts department, it'll be under part 44500-47141. The reason is because this part is sold with a resistor. And because of that, Toyota had to create a part number for you to purchase with the resistor.

So when you order 44500-47141, it'll come with the actuator part 44510-47051 and the resistor

 

I find it strange you can't buy it without the resistor. I changed the resistor when I did mine but I didn't find any issues with the old resistor. All the values were very similar to the new one. And to top it off, it's a pain in the butt to change it under the dash

 

Or it will come with an actuator part, that happens to have a number 44510-47051 visible on it that may never have been its part number, but may be an engineering number, a number for one of its component parts that happens to be on a surface that's visible after assembly. etc.

 

04xxx- numbers are numbers of kits Toyota puts together to conveniently supply some things often needed together.

It's always worth looking to see if there is some 04xxx- kit that includes the thing you're looking for, because it will often include some other miscellaneous bits, like gaskets maybe, that you'll need anyway and that would otherwise be a la carte, and also because, surprisingly enough, the kit often has a much lower price than the thing alone.

 

I'm not sure how many conclusions I'd be confident in drawing from the level of detail that's in the accessible parts catalogs. (I don't even know how much better the dealer-accessible EPC is.)

Often, an 04xxx- kit of something will have been announced in a Technical Service Bulletin about some issue. Sometimes if you go and find that TSB it will list what's supposed to be in the kit. Otherwise it might be like a mystery package until you open it.

The resistor I used to think they included because they had matched the resistance to the properties of each pump motor. But the resistor has its resistance in milliohms stamped on it, and I haven't read of anybody here seeing any that didn't have the exact same number stamped on. The resistance of old ones, when measured, doesn't seem to have changed or anything. Bit of a mystery to me why there's a new one in every box.