Master Cylinder Failure

It would be worth some careful fact-finding before sinking $1200 into it.

My chief concern is that the reported trouble codes indicate a failure to achieve target fluid pressure at the accumulator. There can be several different reasons for that, and there are about 14 pages in the repair manual that detail how to pin down the cause. There was about a ten-year period where if you went in to Toyota with those codes, they wouldn't even bother doing further diagnosis, but would just say "there have been enough problems with these we'll just replace both assemblies under service campaign ZJB" or whatever its Canadian equivalent is called. But with the time/mileage limit on that campaign probably expired, the diagnostic steps in the manual get interesting again. If parts aren't all free, it pays to figure out case by case what really broke.

But I don't know of any obvious way for leaks in a wheel cylinder brake line to produce the codes you've reported. The pressure in question is upstream of those lines. If those valves are not leaking into those lines, I wouldn't expect the reported codes to result. If those valves are leaking ... well, that's the actuator.

I'm not saying a mechanic could never convince me she had found a way for it to happen. But she'd have to make me a convincing case involving the diagrams and whatever actual tests she had done to confirm it was happening.

Toyota uses coated brake lines that are pretty rust resistant, so that makes me wonder: if those lines are eaten through, is rust getting ready to swallow this car whole? That could be a decision influencer. I'm not too spooked by the mechanical complexity of a Prius, but I intensely dislike rust.

 

When I see rust, I expect shit like this to start happening. This leak probably will cause the actuator to go out faster as it keeps trying to apply more pressure.

 

Yes, on most non-hybrid cars the ABS is of a non-integral type that is often sold from the dealer as a single assembly- ecu bolted to the hydraulic assembly (pump/ valve block). In general they fail very rarely (except for Bosch ecu's- but those are available seperately). I think I have replaced maybe 9 or 10 ABS hydraulic assemblies in 30 years?

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It's difficult to say for sure. Failed brake lines are definitely A problem, but it might not be the ONLY problem. Normally if there is a hydraulic leak, I'd expect the system to detect the pressure drop on that line, set a code for that and turn off the solenoid to isolate the leak. The only way I could imagine this could trigger the pump/ accumulator codes was if it DIDN'T isolate the leak and the fluid level got so low that the pump was sucking air (even then I might expect it to set some kind of low fluid code- assuming the level switch worked).

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And come to think of it, that even does make sense, if every use of the brakes ended up sending a bit of fluid out through the leaky wheel cylinder lines, and having to make up the pressure. I had been thinking too much from the "what would set those codes when not braking" angle.

I don't remember that you posted the 3 digit INF code that went with your C1256, but I bet if you had, it would have been 143. One of the ways that can be set is when the pressure is low and a wheel cylinder pressure is short of target while braking.

That could have served as a way to feel more confident the mechanic was on the right track before starting the work.

I hope it stays fixed!

 

Techstream is very useful, and the same hardware that works with less-than-paid-for Techstream works with scrupulously-paid-for Techstream too, so you can put together the necessary hardware to have on hand, and approach the Techstream licensing as your principles guide you. To use it in a scrupulously-paid-for manner, you would sign up here at the "professional/diagnostic" level, and each $65 would give you an authorization key that would allow two days of using the software.

 

Let's hope for the best. I will note that when my brake actuator went out due to excessive pump runtime, the dealer did a full techstream flush first. The system worked flawlessly. For two days.

(I use brake actuator generically to refer to the pump and master cylinder)

 

I think in many cases, strictly speaking, that's "excessive pump runtime due to actuator having gone out".

 

Not wanting to make another thread, so I'll pop into here.

My 220k 2010 just went to the dealer for a IPM Recall. While it was there, the dealer has been trying to convince me that I should absolutely not drive this vehicle off the lot because of the codes concerning the Master Cylinder Leak. They say:

"The brakes could fail catastrophically with no warning. We've had it happen here at the dealership."

I'm skeptical.
1) Never had any brake related codes come up in my owning the car for the last year.
2) Never had brakes leaks, or disappearing brake fluid.
3) I get the feeling they really want to charge me a $100 "Diagnostic Fee" so they aren't eating the entire cost of the IPM failure warranty.

Is there any way of my validating their pointing to this Master Cylinder Failure without TechStream? Will the brake system throw another type of code? If the Brake Accumulator "ABS Assembly" does fail, will it do so catastrophically as they suggest?

 

Plenty of these cars have lost their brake pump and master cylinder. The system is brake by wire and it is common for the brake pump to leak its nitrogen charge. No brake fluid leaks are involved but a complete failure of the brake by wire system defaults you to reduced manual brakes with no power or regen assist. People will be driving normally at speed and sometimes have this failure. Extra long stopping distances can cause a wreck. It is serious and real.

If they will give you a warranty repair on a 2010, jump on it fast. Even if its a $100 diagnosis charge. Verify warranty would be available with the right codes first. My understanding its ten years. Normal discounted cost is at least $2200!

 

The dealership should be willing to tell you what codes they retrieved and are talking about. If you take the car with you, you will be able to confirm the codes, even without Techstream; the brake computer is able to blink its codes for you on three of the dash lights, as you can read about in many threads here.

The "accumulator bellows leaks nitrogen" issue (was recall D0H for 2010s) and the "valves in actuator leak brake fluid internally" (service campaign ZJB for liftbacks) are two completely different issues that have only the word 'leak' in common (even though completely different substances are 'leaking' in the two cases). They get frightfully often mixed up around here.

Either one of those two different conditions will usually progress to noticeable symptoms where you hear the brake pumping its pressure back up much more frequently than usual; codes will be set, and, when things progress to the point that pressure just can't be held up, a long high-pitched beep alarm sounds. Trying to brake without the pressure to assist you means that the pedal feels very high and hard, and you have to step on it way hard to slow the car down, but it does.

That isn't fun, but it is the safer kind of brake failure; it will feel like most other cars do when their power assist has gone out.

An opposite failure mode from that one is the floored-pedal-no-stoppie failure, which is where it doesn't matter how hard you step on the brake pedal because it just goes squish right to the floor and does nothing to the speed of the car. That one is much more rare, which is good news, because nobody likes it.

If there is a problem, there are two different components that might need replacement, so it is good to do a bit of diagnosis to pin a problem down to one or the other if possible.



The normal, new-part, undiscounted, Toyota list prices are (as of this writing) $711 for that top one or $693 for that lower one. Dealers that sell at discount may knock a hundred or so off either price, so if you needed both (and could not apply warranty) you would probably have a parts cost around $1200-ish.

But all of this should start with clarifying what codes the dealer is talking about.

 

I use Dr Hybrid but I've also got the Torque app. Will they show the codes associated with these master cylinder issues?

 

Give it a try, see if any C codes come up. You can post them here.

If you don't get any that way, there are always the blinkenlights.

 

Really appreciate your post. My daughter's 2012 Prius just threw codes C1252, C1253, and C1256 and had a hard pedal. I reset the codes using TechStream and the car is currently driving normally. 2 questions - is there any way to know WHICH of the 2 brake parts is bad? Also, what are the chances it was a fluke and will operate normally for the next months? Anyone here cleared codes and seen it go away? (wishful thinking, I know).

 

For that car, I would dig into the C1253 code first. That indicates an electrical issue that may be keeping the pump from running. If the pump won't run, the other two codes are no surprise.

There are troubleshooting steps for a C1253 code in the repair manual:

Toyota Service Information and Where To Find It | PriusChat

One thing I see there is that C1253 can have nine different "INF" subcodes that would give you more information about what the issue is. If you have Techstream, you can see the INF codes, in the freeze frame for the code.

I don't think the 'fluke' scenario is terribly likely.