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Lexus: Why Does My Brake Pedal Go to the Floor?

There are various reasons why the brake pedal keeps hitting the floor. Learn those reasons and how to avoid them here.

By James Karuga - November 20, 2014

This article applies to the Lexus IS, GS, ES, RX (2005-2013).

Brake failure is one of the scariest experiences possible in a vehicle. The most common type of acute failure is when the brake pedal sinks to the floor when pressure is applied. Understanding why this happens is vital to preventing it. Typically, this is caused by either a lack of brake fluid or a fault in the master cylinder. A failing brake booster will not pressurize the brake fluid and cause the pedal to hit the floor, making the car hard to stop. Overheating the brake fluid can also cause a soft pedal. Generally, this is the result of lots of hard braking or by riding the brakes. Too much heat turns the brake fluid into a thin liquid. Thin fluid requires more pressure than the master cylinder and brake booster can provide, resulting in a pedal that will hit the floor.

Step 1 - Bleed the brakes to purge the air out

Bleeding the brakes will remove any air in the braking system. Brake fluid is incompressible; pressure is transmitted to the brake pads by increasing the pressure on the fluid. When there's air in the system, the air compresses. Since the pressure provided by the brake master cylinder is compressing air and not engaging the brakes, the pedal will feel soft.

Figure 1. Bleeding brake caliper.

Step 2 - Replace the master cylinder

Leaky seals on the brake master cylinder can also cause a soft brake pedal. Take the car into a mechanic if there's reason to suspect the brake master cylinder is leaking. Leaks lower the brake fluid reservoir, causing the pedal to constantly hit the floor when braking. You'll be able to tell if it's leaking by puddles and drip marks on the cylinder.

Figure 2. Lexus brake master cylinder with no leaks.

Step 3 - Refill the brake fluid

Check the brake fluid reservoir under the hood. If level of brake fluid is low, refill it with ATE Super Blue Racing fluid. Low brake fluid is a common cause of a soft brake pedal.

Figure 3. Refill brake fluid reservoir with ATE Super Blue Racing fluid.

Step 4 - Flush the brake system

Dirt and debris can clog the entire braking system. If all else fails, take the car into a mechanic for a full brake system inspection.

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