2004 Brake Problem

It sounds like a couple of possibilities. Depending on what you mean by going on and off several times fast, it could be the anti-lock brakes pulsing the brakes, say if a sensor is dropping out occasionally.

The talk about a lack of power brakes could also indicate a problem with the brake booster, or the check valve between the booster and vacuum source. I would have to look up the power brake booster system to see how they have it set up.

Also there is a system that allows the pedal to move when regenerative brakes are being used to give the pedal a "normal" feeling. That could be malfunctioning.

That having been said, we probably need more information. I understand if you put the vehicle in neutral, regenerative brakes will not operate at all. In a safe place, get up to about 30 miles per hour and apply the brakes till you stop or get the system to act up. If it is a problem with the plunger mechanism or the brake booster, I would expect it to do it at any speed. If it still only occurs at the same speeds as when you first started noticing it, then it could be a wheel speed sensor

Also, does it act up with the engine running or off or both?

The other thing I would do is look around in the engine compartment at the hoses and make sure you don't have one that got disconnected or rodent-chewed.

Hope that helps!

 

There is no vacuum source. The Prius brakes are electric assist. See diagram



A problem with a sensor will reliably set a malfunction that will be stored in memory. This could be something as simple as rust on the rotors, or oil/grease on the rotors

If driven in an area that dumps a lot of road salt in winter, the caliper slide pins could be sticking as well.

Given the age of the car, I believe a brake fluid flush is in order. However, this is NOT a do-it-yourself procedure. You require the dealership scantool to properly bleed the brakes on a Prius. I provided the shop manual section on how to do so, in this post

http://priuschat.com/forums/gen-ii-...em-rear-brakes-no-pressure-when-bleeding.html

Hope this helps

 

Somebody could have put the rear drums back on with a few parts missing. Or missing shims on the front calipers. Who knows. Take it back to the dealer and tell them they fubar'd