Sinking brake pedal Avensis T25

[hJohn]

Hello. The brake pedal in my 2007 Avensis sinks to the bottom but only when vacuum is connected to the brake booster. Is it safe to assume the brake booster to be bad? The pedal is firm and does not sink at all when the engine is off or when I disconnect the vacuum hose to the brake booster.

Is there any type of test I could do to determine what is causing this problem so I don’t just throw parts at the car?

[avensis_2018]

hi i you need to replace the master booster brake pump, it with the brake oil tank, you can buy chinese one to replace it around 100$ and they are good also change the brake oil with it!

good luck.