Stability /traction control, Brake, ABS, ((!)) lights stay on C1391

There isn't any pressure in there to speak of that would be "relieved" by doing that. The accumulator is normally kept pressurized (at a pressure that doesn't depend on any impact) and the rest of the lines, etc., return fluid back to the reservoir and rest at atmospheric pressure when you're not braking.

If you have a C1391, accumulator pressure is probably leaking down, which is what the code means. Do you have a scan tool you can use to watch the accumulator pressure reading?

 

I think you can just hit the brakes while you're sitting in the parking lot and see your pressures and do their thing and you can leave the car just sit there with the thing connected and see the pressure going down and then the pump coming on and the pressure going back up and this constantly repeats while you're not even touching the pedal which is the point of the whole exercise when the car is sitting nobody's touching the pedal car sitting there running everything ready ready for you to put in gear and back out of your parking space or whatever it is you're going to do but you do nothing Don't put your foot on the brake don't touch the gas don't even fiddle with the radio just sit there and look at text dream and the appropriate screen and you will see why you're getting the 1391 the pressure will go down and then you will see the pressure go up and you ought to hear your break pump ing the noise. And then this will just keep repeating itself which it should not be doing essentially.

 

Yes, if you have it graph the accumulator pressure, it'll be kind of sawtooth-shaped: slowly going down, until the pump cycles and bumps it back up, then slowly going down again, and so on.

The key is it normally goes down really slowly. Sounds like yours isn't.

 

No. It has an internal leak, can't hold pressure. That's the hissing noise, and the reason the pump has to keep running to pump it back up. If you've already heard and noticed it doing that frequently, then there's no need to mess with a graph of the accumulator pressure to just show what you already plainly hear.

 

If there are a bunch of lights coming on, there is more than one trouble code. (It may be that there is just one trouble code and other codes referring to it, but it is worth checking.) Would you be able to post all of the trouble codes you have the next time the lights come on?

If you do not have a scan tool that will show them, you can retrieve the brake system trouble codes (any codes to do with the ((!)), ABS, or skiddy-car traction lights) this way:

Blink (a/k/a Flash) Codes – How to. | PriusChat

"My car seems to work better after the warnings come on, maybe the computer is crazy" is an idea people kind of routinely get around here. More likely it means the computer, once it detects failing stuff, switches to a fail-safe mode that works better than the failing stuff does.

 

@Ledorian did it work? This is a known problem and there were a bunch of TSB's on many Toyota and Lexus models going back to 2006. I don't know how they got away from a recall. The cost to change these is around $4k. I hit this issue on my Lexus and it is 115k. I don't know what to do. The current value or my car is around $5.5. I don't know whether I want to spend 4k to use the car for another 5 or so years. I am a Toyota / Lexus through out my life (5 cars) and I am VERY DISAPPOINTED with TOYOTA.

Is there any other way to fix it without spending $4k?

 

I don't know whether this will fix the issue.

 

You shouldn't spend 4K to fix the brakes on this model The two parts together are only 1400 I think about seven a piece there may be even a rebuilt option or something if you scour the internet carefully getting used low mileage takeouts as possible from the JDM market there's ways to skin that cat If you want to spend 4K I guess you can If you want the new parts it'll be about 16 and then you can put them on or not.