Your brakes work hydraulically: pressing the pedal pushes fluid down the lines to squeeze the pads onto the discs. Too little fluid, or old fluid that has absorbed water, can mean a soft pedal or, in the worst case, brakes that fade on a long downhill. The check takes one minute.
You'll need
- A clean cloth
- Only if topping up: a sealed, unopened bottle of the fluid type printed on the reservoir cap (e.g. DOT 4)
⚠ Safety first
- If the brake pedal feels soft or spongy, sinks towards the floor, or the car pulls hard to one side when braking, don't drive. Get the brakes inspected first.
- Brake fluid strips paint. Wipe up any drips immediately and rinse the area with water.
Step by step
- 1
Park level, engine off
Park on level ground with the engine off and the bonnet open.
- 2
Find the reservoir
Look for a small translucent plastic tank, usually at the back of the engine bay on the driver's side, mounted on the brake master cylinder. The cap normally says 'brake fluid' and shows the DOT type.
- 3
Read the level
Without opening it, check the fluid sits between the MIN and MAX marks. Fluid levels drop slowly and naturally as brake pads wear, so a level near MIN on a car that's due for pads is not unusual.
- 4
Check the colour
New brake fluid is clear to light golden. Dark brown fluid is old and has absorbed moisture, which lowers its boiling point. It's due to be replaced even if the level is fine.
- 5
Top up only if below MIN, then get it checked
Wipe the cap clean before opening it so no dirt falls in. Top up to MAX with the exact fluid type on the cap, from a freshly opened bottle, and close it straight away. Then have the brakes checked: low fluid almost always means either worn pads or a leak.
Pro tips
- Never mix DOT 5 (silicone-based) with DOT 3, 4 or 5.1 (glycol-based). Use only what's printed on the cap.
- Brake fluid absorbs moisture from the air over time, even in a sealed system. Most manufacturers specify a change every 2 years.
- Motorbikes usually have two reservoirs: one on the handlebar for the front brake, and one near the rear brake pedal. Check both.
Stop and get a mechanic if…
- You need to top up more than once.
- Wet patches inside a wheel or on the inside of a tyre, which can be a brake-fluid leak.
- The red brake warning light stays on with the handbrake released.
General guidance only. Your owner's manual has the final word on specs, fluids and procedures for your vehicle. Last reviewed 24 September 2026.