ABS, Brake and Traction lights on with codes C1252, C1253, C1256, C1365

Looks like my ISA 10 model . I'm guessing the part on the firewall with all the computer parts is the part that is probably failing but I don't know that there are tests to separate that You can use a mechanic stethoscope shut down the car listen for leaks at both units see if you hear any leaking down going on and that's kind of a dead giveaway but it seems the things that do the computer controlling are in the part that goes on the firewall and then I guess there's a different rack with the pump and something else with it It's two pieces If you misdiagnose you replace the wrong piece and then have to buy the other piece in the manual which is posted somewhere out in the wild there is extensive testing procedures that you need to follow to a t so you're not buying $1,500 worth of parts versus like seven this is all stateside prices that I've looked up recently this is for new parts from whoever I don't think any of this is available in the aftermarket sometimes the JDM importers will grab you one or we'll have some of these parts You have to check around.

 

You've got these two things under the hood:



The bottom thing has an electric pump (the smaller round bit) that puts brake fluid under pressure into an accumulator (the bigger round bit). That pressurized brake fluid is used by the upper thing, which controls the fluid and sends it to the brakes.

The pump usually runs for just a second or so whenever the accumulator pressure gets a little bit used up. Because the pump starts when only a bit of pressure is used up, it doesn't normally take longer than a second or so to pump back up. It sounds a little bit like a rattlesnake. Or a joy buzzer.

Here's where it might be important to know exactly what you've been hearing. A lot of people with old enough cars get a problem where the pressure tends to bleed off, and the pump has to keep repeatedly running to build it back up. That's one kind of problem. It's usually a "replace that top thing" kind of problem.

But it sounds like maybe your pump just wasn't running at all. If you get that low-pressure warning beep and you're not hearing that rattlesnake or joy buzzer trying to build the pressure back up, well, nobody needs to look any further to see why the pressure's too low.

If the mechanic bopped the pump with a hammer and suddenly a rattlesnake noise started, and a few seconds later the low-pressure beep stopped, then to me that could suggest the motor brushes in the pump are just worn out. That would be more of a "replace that bottom thing" kind of problem.

 

It won't hurt the system further, but the beeping is warning you that there's low or no boost pressure, so you might only be braking the front wheels and only with the force your own leg can make. So be careful that driving this way doesn't hurt you.

Also, in a crash, there's a chance the brake system gets further damaged.

 

If you count 90 seconds after switching the car off, and you hear a sort of click squish click click squish click, that's just the brake system doing its self test. Not a concern. (However, if you are ever planning to do some brake work, don't start taking things apart before that test happens; you don't want anything pressure-tested while disassembled.)

It is normal for the level to rise slowly when the car is off. Even in a non-worn system, the accumulator does not hold pressure perfectly; the fluid slowly escapes back to the plastic reservoir. That's why the pump normally has to run for a few seconds when you first open the car in the morning. It has to pump a bunch of fluid back to the accumulator, and the reservoir level drops.

The marks on the reservoir are placed for when the pressure is zeroed down and all the brake pads are fresh. So the fluid should be right at MAX then, and go a bit lower when the pump runs, and return to MAX slowly after the car is turned off. As the brake pads wear, the levels will stay a little lower.

You seeing it above MAX when it is zeroed down probably just means that somebody didn't understand how that's meant to work, and topped off the fluid some time in the past when it wasn't zeroed down (so it was supposed to be below MAX), and now it is slightly overfilled. Or somebody topped it off while the brake pads were old, and later new pads were installed, and now it is slightly overfilled. There's a bit of extra room in the reservoir so that is probably not much of a problem.

Of course, if your pump has ceased running at all, then you're going to see the zeroed-down levels pretty much any time you look.

The whole assembly is the only way Toyota sells it. I sometimes see threads with people scavenging individual bits and pieces of assemblies from other sources. If you have an easy source for the pump on its own you could try that, but I have no sense of how easy or practical it is to disassemble the assembly.

 

I had same exact problem. Same lights same sound same hard brakes.

1252 1256 where the same codes I had. Checked for sensors/ leaks / oil/ brake fluid… everything else that could cause abs problems that’s minor. Ultimately I found a honest mechanic and he changed The ABS CONTROL MODULE AND ABS ACCUMULATOR ! my Prius v 2012 is now perfectly running. No lights, no hard brakes, nothing. You are wasting your time if you don’t get the accumulator and control module because trust me I looked for every single possible way to avoid it. Got both to be installed flr $1800 altogether. I was blessed with such a honest mechanic. Good luck.

 

Is that with the 2012 Prius v mentioned in your profile? I see that you've made this identical post on several threads, some Gen 2 and some Gen 3.

There are some differences between the generations: if you meant a Gen 3, it sounds like your mechanic replaced two assemblies under the hood. In Gen 2, the accumulator is integrated with the actuator. In Gen 3, they're separate assemblies and you don't always need to replace both; sometimes you can diagnose which one is at fault.

Also, there are other possible causes of the codes. If the pump can't run for an electrical reason, for example, there will be too-long-pump-run and low-pressure codes.

So a person wouldn't be wasting time, to go through the recommended diagnostic procedure before going straight to the big-bucks replacement. If the replacement is what's needed, the diagnostic procedure will tell you that. If you want to save time and just bet that way, and you win the bet, that rocks. But it'll suck for the guy who jumps right to the big-bucks fix and it still doesn't work, and then finds out the 5¢ wiring fix takes care of it.

NB when I say "go through the diagnostic procedure", I just mean the steps in the manual for pinning down what's causing the problem. I don't mean the kind of further wishful thinking people sometimes go through before finally getting it fixed.

 

That video is for a conventional car with a vacuum-powered booster, nothing like a Prius at all.

Usually, those vacuum-powered boosters can hold enough engine vacuum for two or three good strokes of the brake pedal with the engine stopped, after which it will get hard.

In a Prius, the pressure accumulator holds more like twenty or thirty strokes' worth of pressurized fluid. You can do a similar test, and pump the pedal 20 or 30 times or so, and find that it suddenly gets quite hard. But to do that, you have to first disable the pump, because otherwise it will come on to replenish the pressure, even when the car is off. (Trivia: this test doesn't work in Gen 2, which assisted your braking a different way than all the other generations.)

It's a generic car part name; nothing in a Prius is actually called that. There are two things a person might mean when they say it: they could mean the ABS actuator (the thing with electromechanical valves to control the individual wheel brakes for ABS), or they could mean the ECU that's in control of all that (in the Prius, Toyota calls that the "skid ECU" because it is in charge of the electronically controlled braking, the ABS, and the skid control functions).

The parts move around in different Prius generations, but in a Gen 3, if you look back at the drawing in post #4, the upper unit there contains both the ABS actuator and the skid ECU. So if that assembly has been replaced, both of those parts have.

 

So we had these symptoms in a 2013 prius and decided to change out the brake booster assembly w/ master cylinder. We could hear the pump still clicking and assumed it was still good. That said, after taking out the assembly and placing the new one in, we couldn't get tech stream to bleed the brakes nor did it appear that the new assembly was getting power in any way. My mechanic has done 100 of these and we're not sure what could be causing the assembly to not get power. The fuses seem to be okay and when we plugged in the original assembly just to check, now it too doesn't seem to be getting power either? Any tips or ideas as to what may be causing this? We think it could be either the abs 30/30/40 fuse although it appears to be in tact and he said something about the 12v possibly. Just tossing this out there to see if anyone had run across this issue and has a solution.

 

Maybe a new thread "brake actuator not seeming to get power after replacement"? That's kind of an unusual situation, sets it apart from this thread a little.

Have you arranged access to a multimeter and the wiring diagram?

Toyota Service Information and Where To Find It | PriusChat

The two 30s in that 30/30/40 fuse are for power specifically to the pump motor. The brake system other than the pump motor gets power through ABS MAIN NO. 1, ABS MAIN NO. 2, and IGN.

What are the observations leading you to say "nor did it appear that the new assembly was getting power in any way"?