Squeaking brake paddle

can you post a recording?

 

This is a classic Prius problem. It is air bubbles going through the orifices in the brake "actuator" (simulates hydraulic pressure when you step on the brakes). The "bark" or "chirp" gets exaggerated at altitude (low air pressure). My 2004 Prius was fixed by a brake bleed at the dealer. There is an old TSB on this issue.

JeffD

 

The brake actuator TSB that I assume you are referring to was only for the 2004-2009 Prius and the 2006-2007 Toyota Highlander AFAIK. The only "official" symptom per Toyota was the ABS and VSC warning lights coming on as well as particular codes stored. However many people experienced auditory symptoms before they later got the warning. There is a "buzzing" sound that is normal when the brake actuator is running, but it should last only a few seconds. People with a defective brake actuator experienced that it ran continuously or at least much longer than normal when they were stopped at a light. Unfortunately most Toyota dealers wouldn't replace the actuator for free unless the codes were stored, although some people lucked out and the dealer replaced it anyway since the mechanic could hear the problem.

The other symptom was the barking or chirping sound, again normal for a little bit of that occasionally, but in this case it was persistent. However this could also be caused by air in the fluid, which could usually be solved by bleeding the brakes (as you experienced). Most people just went ahead and had the brake fluid replaced at the same time. If that didn't fix it, again if no codes than no free replacement. Many people with either the persistent buzzing or persistent chirping were hoping they would get the ABS and VSC warnings before 12/31/2017 which is when the extended warranty for the issue expired.

 

Where are you located? The Chirp (bark) is exacerbated at altitude due to lower air pressure.

JeffD