Why does my brake pedal feel spongy or soft?

Press the brake pedal. It should feel firm and stop at a consistent point. If it feels squashy, travels further than usual or slowly sinks while you hold it, something in the hydraulic system is not right. The usual culprits are air in the lines, old fluid, a leak, or a worn component.

Brakes work by pushing fluid through pipes and hoses to the calipers or wheel cylinders. Fluid cannot be compressed, but air can, which is why a spongy pedal is such a clear warning. Below we cover the causes, what you can check safely and what to do about it.

What makes a brake pedal feel spongy?

Air in the system is the classic cause. It can get in when a component has been replaced and the system was not bled properly, or through a leak that lets fluid out and air in. Because air compresses, some of your foot movement goes into squeezing the bubbles instead of applying the brakes.

Old fluid is another cause. Brake fluid absorbs moisture over time, and under heavy braking the heat can turn that moisture into vapour, giving a soft or fading pedal. Flexible hoses that have swollen internally and worn pads or adjustments on drum brakes can add to the effect.

Is a pedal that sinks to the floor dangerous?

Yes. If the pedal slowly sinks while you hold steady pressure, fluid is probably leaking past a seal in the master cylinder or out of a pipe, hose or caliper. This can lead to a sudden loss of braking, so do not rely on the car.

Stop driving if the pedal goes to the floor, needs pumping to work, or a red brake warning light is on. Pull over safely and ask for advice before moving the car again.

What can I check safely myself?

Park on level ground with the engine off and look at the brake fluid reservoir under the bonnet. The level should sit between the minimum and maximum marks. A low level can mean worn pads, since the fluid level falls as pads wear, or a leak. Your handbook shows where the reservoir is and which fluid type to use.

Do not top up with random fluid. Brake fluid comes in different specifications, and mixing the wrong types can cause problems. Also look under the car and at each wheel for damp patches or drips, and check the pedal feel with the engine running and off.

• Fluid level below the minimum mark
• Fluid that is very dark or cloudy
• Wet marks on the inside of a wheel or tyre
• A pedal that feels firmer with the engine off than on, or the reverse

How does a garage fix a soft brake pedal?

The garage starts by finding the reason instead of just bleeding the brakes. It checks the fluid level and condition, looks for leaks at the pipes, hoses, calipers and master cylinder, and inspects pads, discs and drum brakes. Only once the cause is found is the system bled to remove air, often with a full fluid change.

Cost depends on what the inspection finds. A bleed and fluid change is a smaller job than replacing a hose, a corroded pipe, a caliper or a master cylinder. The make and model, and how accessible the parts are, also affect labour. At Automaster, a garage at Longcombe Cross near Totnes, we explain the cause and the options before starting.

Can a soft pedal happen suddenly or build up gradually?

Both happen. A gradual softening points to ageing fluid or slowly developing wear. A sudden change, especially after work on the brakes or after a heavy stop, suggests air has entered or a leak has started.

Whichever applies, mention when you first noticed it, whether it changes when the car is hot, and whether the pedal feel is the same on the first press as on repeated presses. That information helps the diagnosis.