Brake pedal goes to the floor when the engine is running

MIKEDOULABI

MEMBER
2004 LEXUS RX 330
3.3L
V6
2WD
AUTOMATIC
90,000 MILES

Hello,

Brake pedal goes to the floor when engine running. New master cylinder, replaced brake fluid, booster is good. With the engine off pedal is rock hard.
Thanks.

Sunday, September 23rd, 2018 AT 7:55 PM

1 Reply

KEN L

MASTER CERTIFIED MECHANIC
48,363 POSTS

Hello,

Does this car have ABS? If so you have air trapped inside the ABS unit that is allowed into the system when the engine is running. To be sure I have had people use vise grips to gently pinch off the flex hoses to check to see if the problem is at the wheels or master related.

This guide should help it shows the reasons for the brake pedal going to the floor.

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Please run down this guide and report back.

Cheers, Ken