Brake Pedal Goes to the Floor? Top Causes and How to Fix It
About this video
You press the brake pedal and it keeps sinking toward the floor. Maybe it goes soft at a stop light, maybe it drops slowly under steady pressure, maybe it went all the way down with no warning. In this video our ASE Master Technician with over 30 years of experience explains every cause of a sinking brake pedal, how to tell them apart, and how to fix each one.
This is a safety issue, not a maintenance item. A brake pedal that goes to the floor means the hydraulic system is either losing fluid or losing pressure, and it will get worse.
WHAT TO DO IF IT HAPPENS WHILE DRIVING:
Pump the pedal rapidly to try to build pressure
Downshift to let the engine slow the vehicle
Use the parking brake gradually, not all at once
Steer to a safe shoulder and get off the road
Check the brake fluid reservoir once stopped
Do not keep driving it. Have it towed
HOW THE SYMPTOM POINTS TO THE CAUSE:
Pedal sinks slowly under steady pressure with no visible leak, that is almost always a failing master cylinder bypassing internally
Pedal is soft and spongy but holds, that is usually air in the lines or old contaminated fluid
Pedal goes to the floor and fluid is low, you have an external leak at a line, hose, caliper or wheel cylinder
Pedal is hard and the car barely stops, that is a brake booster or vacuum supply problem
Pedal pulses or is low only after hard braking, look at ABS operation and rotor condition
COMMON CAUSES OF A SINKING BRAKE PEDAL:
Failing master cylinder with internal seal bypass
Air trapped in the brake lines
Brake fluid leak at a rubber hose, hard line, caliper or wheel cylinder
Leaking rear wheel cylinder on drum brake vehicles
Old moisture contaminated brake fluid boiling under heat
Corroded and swelling brake line
Failing brake booster or leaking vacuum check valve
ABS module or ABS pump failure
Excessive caliper piston travel from worn out pads
Rear brake shoes out of adjustment
Improper bleeding after a brake job
SYMPTOMS THAT COME WITH IT:
Brake warning light or ABS light on the dash
Low brake fluid level in the reservoir
Longer stopping distances
Spongy or mushy pedal feel
Pedal drops slowly when held at a stop
Brake fluid puddle or wet spot near a wheel
Fluid dripping onto the driver side carpet, which points at the master cylinder
Grinding or squealing along with the low pedal
RELATED FAULT CODES:
C0035 through C0050 Wheel speed sensor circuits
C0110 ABS pump motor circuit
C0265 ABS relay circuit
C1095 ABS hydraulic pump motor
Brake fluid level and brake switch codes vary by manufacturer
Applies to nearly any vehicle, including Toyota, Honda, Ford, Chevrolet, GMC, Dodge, Ram, Jeep, Chrysler, Nissan, Hyundai, Kia, Subaru, Mazda, Volkswagen, Audi, BMW, Mercedes-Benz, Volvo, Lexus, Acura and Infiniti. Hydraulic brake systems work the same way across every make, disc or drum, ABS or not.
Many modern vehicles require a bidirectional scan tool to cycle the ABS module during bleeding. Without it, air stays trapped in the ABS unit and the pedal stays low no matter how many times you bleed it. The YOUCANIC UCAN-II Pro performs ABS