C1391 - Abnormal leak in accumulator - 2012 Ct200h

I’ve the same dealer computer as this model . I know this is kinda common on Prii gen 3. JDM in NJ has both pieces that get fooled with during this operation low mileage imports from Asia . I’ve both pieces sitting here at the ready.its usually internal so no matter what we know . probably gonna get replaced . The booster gets hammered by foot . The accumulator has electrics and pump . Both subject to hi wear. No?

 

Right, an external leak is almost never what this is. It will be an internal leak, where fluid that is supposed to be held under pressure, ready to operate the brakes for you, just slips right back to the reservoir.

If you watch the reservoir closely, you should see the level going down a bit every time the pump runs, as the fluid is pumped into the accumulator. But in the three seconds between pump runs, the level goes back up, as the fluid simply leaks back.

However, you can't take the fortune cookie, "abnormal leak in accumulator", completely literally. The accumulator and the booster are two separate parts in this model, and they both have return hoses to the reservoir, and either one can be where the leak is. In historical experience it is more often the booster (also known as 'actuator'—not to be confused with 'accumulator'). It is more complicated, containing more than a dozen valves that see regular choreographed use. By comparison, the accumulator has one check valve and one overpressure relief valve, and the latter sees no action at all in normal operation, so it hasn't even got any reason to wear out.

That's a little surprising, at only 3 seconds to leak down (which is flat-out awful; in a good unit that takes hours), I would have expected a fairly audible rushing noise. But then, to some extent, hissy noises come from restrictions, and as a leak gets worse beyond some point, it may get quieter. That's unfortunate; if you could hear it better, you would have a clearer answer to the which-unit-needs-replacement question.

In this video, at around 8:15 the hissing is audible, and the mechanic describes localizing it with a stethoscope. But that was in a unit taking more like 15 seconds to leak down, so yours is about five times as bad.

(One little distraction warning: around 4:20 to 5:20 in that video, he's talking about a recall that was actually for a different issue.)

 

Try not to make the same mistake as the guy in the video, mixing up the different issues. The yellow sticker orientation business comes from the D0H recall, which was a different issue (some accumulators would crack inside and lose nitrogen gas).

ZJB is not a recall, rather a warranty extension, and it is about this kind of internal fluid leak. No label-orientation business for ZJB.

And it will probably pay off, as it did in that video. You might notice in that case the customer had already bought both units, but the mechanic stopped as soon as the booster replacement solved the problem. The accumulator is a much more grueling task. (In a Prius, anyway. I don't know if the access is better in a CT200h.)

Hope springs eternal, but of course it's a distant hope in a situation like this one, where not only is the ECU telling you a leak problem exists, but it's tough to argue when you also plainly hear and see the physical consequences happening.

 

More than that.

If you are really not seeing more than a tiny level change, you might be that rare soul who really does have the lost-gas (D0H) rather than the fluid-leak (ZJB) problem.

Only gases compress, so a can with all the gas lost wouldn't be able to hold pressure long at all. A can with a very small amount of gas left would build pressure with a very short pump, and lose it quickly too.

Maybe that changes the plan....

 

If Toyota got started on a D0H accumulator-replacement job, and they thought the gas had exfiltrated from there into the actuator/booster, they would officially, umm, )mumble( replace both )mumble(.

On the bright side, the accumulator replacement is probably a little less grueling if the actuator is already out of the way.

For replacing the accumulator by itself, there's a WMV video showing the technique they cobbled up for the D0H recall, when they faced the prospect of having to do 89.000 of the things the original way (which required removing the car's suspension for access).

https://techinfo.toyota.com/techInfoPortal/staticcontent/en/videos/cp/D0H_full.wmv

 

I'm in a similar situation, my 2013 Gen 3 Prius has brake, ABS, traction, and ((!)) lights on. They all turned on at once when I hit the brakes hard, going from 20 mph to 6 mph, but I rear-ended a car in front of me at about 6 mph. Other than ABS, Brake, light, Traction ctrl, and ((!)) lights turning on, there was no obvious damage to any vehicles.I've cleared it numerous times, but after traveling 10 to 30 miles, I keep getting the code C1391. The odd thing is that after I clear the codes and go for a drive, the car jerks when I press the brakes and bring it to a complete stop. I'm leaning toward bleeding the breaks and replacing the brake fluid as my first option.