An essential part of brake system maintenance is checking your brake fluid. Low brake fluid levels or unusual colors could be the result of internal damage or simply a sign that your brake fluid was not sufficiently filled last time fluid was added. Keep your brakes operating effectively and promote safety on the road by learning how to check brake fluid and knowing common signs that you need to refill your brake master cylinder reservoir.

Need a Fill Up?

Importance of Checking Your Brake Fluid

Low brake fluid can dramatically reduce the effectiveness of your brake system. If you experience a spongy feeling while pressing your brake pedal, or your brakes aren’t working efficiently, it’s time to check your brake fluid. Low or contaminated fluid can cause your brakes to fail while you’re on the road, so check your fluid today and find out if you need more brake fluid.

There are a range of related brake components that could be causing your brake fluid level to drop, so it’s a good idea to inspect your entire brake system. If you refill your brake fluid and it doesn’t solve your braking issue, inspect your brake pads, rotors, calipers, and brake lines for any signs of damage, extreme wear or leaking brake fluid.

Find Your Brake Master Cylinder Reservoir

In order to check your brake fluid, you first need to find the brake master cylinder reservoir. This reservoir is typically a plastic canister that is mounted near the firewall at the rear of the engine compartment. It’s usually near the driver’s side brake booster, near the brake pedal.

If you’re having trouble finding your brake master cylinder reservoir, consult your owner’s manual. Most reservoirs in vehicles newer than the 1980s are made of translucent plastic and have a line visible on the exterior of the reservoir to indicate the fluid level.

Older vehicles have a metal reservoir with a clamp securing the lid. If you have an older vehicle and an anti-lock braking system, check your owner’s manual for more information. These vehicles typically require you to pump the brake pedal between 25 and 30 times before opening the reservoir. When you’re ready to open it, thoroughly clean off the lid before using a screwdriver to pry open the clamp and open the lid. You should see a fluid line on the interior of the reservoir.

When you need to open your brake master cylinder reservoir, be sure you have everything prepared beforehand. Exposure to moist air can compromise your brake fluid. This can happen if you leave your brake fluid container open for too long. Depending on your climate and air quality, exposed brake fluid can be compromised in as little as 15 minutes. Keep your brake fluid container and master cylinder reservoir sealed as much as possible.

Inspect Your Fluid Level and Color

Check to see that your brake fluid level is up to the recommended fill line. If it isn’t, you may need to refill your brake fluid. However, low brake fluid can also be caused by worn-out brake pads. This is because with thin brake pads, the caliper piston will need to go a little farther in, lowering the fluid level in the reservoir.

If you see a low brake fluid level, inspect your brake pads or ask a professional mechanic to perform a brake pad replacement. After your brake pads are replaced, then you can inspect your fluid level again and determine whether you need to top off your brake fluid or not.

Even if the brake fluid is at the correct level, inspect the color of your brake fluid. Dark fluid could have dirt and other contaminants in it. As dirt enters the system, or as your brake fluid breaks down over time, it becomes less efficient. This can begin to damage your hydraulic components, causing exponential damage and decreasing the efficiency of your brake system.

How to Add Brake Fluid

As a general guide, consider replacing your brake fluid every two years. This will promote efficient use and keep your brake system operating safely for years to come. Choose the exact brake fluid recommended by your owner’s manual or an experienced mechanic. Mixing brake fluid, using the incorrect formula or overfilling your brake master cylinder reservoir can cause damage to your vehicle and prevent your brakes from working properly.

Most brake systems use either DOT3 or DOT4 brake fluid. You’ll find the exact formula for your vehicle either printed on the brake master cylinder reservoir cap or in your owner’s manual. If you can’t find the correct formula, ask an AutoZone associate to look up the right fluid for your vehicle. This crucial step can prevent you from damaging internal seals and other hydraulic components in your brake system.

If you need to top off your brake master cylinder reservoir, purchase the correct brake fluid and gather your safety gear. Brake fluid can be toxic and is highly corrosive, so you’ll need to ensure that it doesn’t come in contact with your skin, eyes, or any painted part of your vehicle. Any rags with large amounts of brake fluid should be disposed of at your local hazardous waste center.

After topping off your reservoir, simply replace the cap and test your brakes. Your brake system should be operating effectively. If you need to bleed your brakes and replace the brake fluid instead of simply adding more, consult your owner’s manual and your local auto mechanic. Replacing fluid requires you to bleed the lines and refill your brake lines and master cylinder reservoir while removing any trapped air.

Common Causes of Low Brake Fluid

Continue to carefully inspect your vehicle after topping off your brake fluid. Low brake fluid is typically a sign of worn-out brake pads or a leak in your brake system. If the fluid level drops soon after refilling it, it’s time to check for a leak and repair your brake system.

If you’re unable to check brake fluid on your own, or you think there may be a leak in your system, don’t hesitate to contact a local AutoZone store. We’ll discuss the right brake fluid for your vehicle and help you find the repair service you need to restore your brakes and keep your vehicle operating safely.

Advice, how-to guides, and car care information featured on and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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