Join Date: Apr 2004
Location: Cape Cod, Massachusetts
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Re: Master Warning Light
No, this one would have no indication of a fluid loss. The brakes are mainly pressurized by the accumulator. (Picture a ball with a membrane dividing the center.) On one side of the membrane is hydraulic brake fluid and the other an inert gas. The pressure is maintained by the membrane forcing the hydraulic pressure when the brakes are applied. There is enough pressure stored in the "ball" by the movement of the membrane for many brake applications. At a certain setting the electric hydraulic pump comes on to re-establish full system pressure. That's the noise you hear when the electric pump comes on. The brakes can be powered by either system and you get a separate warning light when the pressure is too low in either. The leak in the accumulator is usually in the "gas" side of the membrane. Your pump then runs more often. Then one or the other warning light illuminates. Until you get any one steady light you really have no problem. Same as just about any system in the Prius. They have always told you to ignore all unusual sounds and drive normally until you get a steady "idiot" light. The occassional one should be overlooked as worthless as even the Toyota dealer will be confused.
My guess is that sometime in the future you will have to have the accumulator replaced. It could be next month or next year. Good luck!