00 4Runner 4x4, 06 Prius
Join Date: May 2006
Location: Chapel Hill, NC
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As I'm sure you know, braking in the Prius is in part regenerative braking from the MGs and mechanicial braking with the conventional brakes.. The controller system that makes the decision about how to operate these two modes of braking is complex and one thing that will cause problems is if air gets into the braking actuator system, either due to low fluid which you mentioned or as a result of brake repairs..
Per your note, it sounds like either you have a fluid leak in your system or, whoever did the brake work did not properly bleed the system and reset the DTCs (diagnostic error codes) in the braking controller, which can get set when bleeding. (DTCs are in the braking controller itself which is different form OBDII diagnostic codes.)
In any event unless you have the factory service manuals, specifically Volume III Section BC and can do this type of work, you need to return the vehicle to whoever did the brake work and has either the Toyota intelligent tester to check the braking system and if all is well, reset the DTCs or use the manual method in Section BC pages BC-38 - BC40 to reset the DTCs assuming all else is well with the system.
Regarding the loud tone were there error lights lit up on the instrumental panel when this occured?
Obviously your car is telling you there is a significant braking system issue. Call the dealer or mechanic who is competent on the Prius braking system, first is it even safe to drive to the service location? or does it need to be picked up by a roll back vehicle hauler and taken in for repairs. .
Last edited by dandeman; 06-03-2018 at 09:08 PM.