The Prius brake system is interwoven with the hybrid brake system so both the friction (wheel) brakes and hybrid motors can seamlessly slow the vehicle while providing consistent pedal feedback to the driver. As a result the brake system on 2004-2009 Prius can make some odd noises (likened to a buzz or a squish noise) when the pedal is first pressed. The 2010+ Prius has a similar noise, sometimes described as a buzz.
For all Toyota Prius, these noises don’t indicate a malfunction with the brake system, but are rather small amounts of air stuck in a high pressure accumulator (2004-2009) or are due to the actuating behavior of the accumulator (2010+).
For 2004-2009 Prius owners, the first step in repairing the condition is to bleed the entire brake system of any air through the Techstream diagnostic tool’s air bleed procedure. This removes air from the accumulator (stores high pressure brake fluid for use later), ABS module (directs brake actuation as needed in conjunction with TRAC/VSC and traditional ABS), pedal stroke simulator (simulates the pedal feel of solid brakes even though the hydraulics may not be needed at that time), lines, calipers and wheel cylinders. If this does not improve the noise, replacement of the brake actuator is required as per Toyota repair TSB T-SB-0307-08. Below is the actuator circle:
For 2010+ Prius owners a recalibration of the Brake Actuator Skid Control ECU to version F152647108 (for 15″ wheel), F152647128 (for 17″ wheel) or later version remedies most concerns. CARspec recommends replacement of the brake fluid similar to the 2004-2009 Prius repair as well to eliminate all variables.
As Eden Prairie and Chanhassen’s Toyota and Lexus repair specialist, CARspec is happy to help Prius owners of any vintage repair this nuisance concern most auto mechanics misdiagnose!