How to Check Brake Fluid

Updated: Aug. 27, 2019

Make sure the corrosion inhibitor in your brake fluid hasn't worn out

FH08APR_CHEBRA_01-2Family Handyman
Here's how to check your car's brake fluid to make sure the corrosion inhibitor hasn't worn out. It protects the steel brake lines from rust.

You might also like: TBD

Check your brake fluid condition

how to check brake fluid

Photo 1: Dip the strip

Dip the test strip into the brake fluid reservoir and wait for it to change color.

how to check brake fluid

Photo 2: Compare colors

Compare the test strip with the color chart of the brake fluid tester to determine the condition of the fluid. Replace your brake fluid if the color of the strip falls in the “required service” category.

As with every other fluid in your car, brake fluid contains a main ingredient along with protective additives. The main ingredient in brake fluid doesn’t degrade, but the additives do. The most important additive is a corrosion inhibitor. The corrosion inhibitor prevents internal rusting of steel brake lines, calipers and ABS (antilock brake system) components. Once the inhibitors are exhausted, even minute amounts of moisture can cause dangerous and costly corrosion.

Plus: Learn what to do when your brake light comes on.

Most car manufacturers recommend a complete brake fluid flush every two years or 24,000 miles. Rather than rely on a general recommendation, you can test the actual condition of your brake fluid. To check your brake fluid, remove the cover of the master cylinder and dip a strip into the fluid. Shake off the excess fluid and wait 60 seconds before comparing the color of the strip with the guide on the brake fluid tester package. The guide tells you when it’s time to change the fluid. Find a package of 25 BrakeStrip test strips at

Required Tools for this Project

You’ll need plastic gloves to check brake fluid.

Required Materials for this Project

Avoid last-minute shopping trips by having all your brake fluid tester materials ready ahead of time. Here’s a list.

  • Brake fluid test kit