How to Check Your Brake Fluid

Your vehicle’s brakes are perhaps the most important safety system it has, and 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 the last time fluid was added.

Adding brake fluid can cost less than $5 for a new 12-ounce container. But often, checking brake fluid to find out its low indicates there’s a problem somewhere in the system, and other brake repairs are more expensive. Even more concerning is the potential for an accident if your brakes don’t work properly.

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.

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 is 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. 

Signs of Low Brake Fluid

The hydraulic part of the braking system is closed, meaning that the fluid is not consumed and won’t dissipate under normal circumstances. That doesn’t mean there won’t be variances in the fluid level, though. One of the leading causes of low brake fluid is brake pad or shoe wear since more fluid is required in the lines to extend the calipers and wheel cylinders to stop your car. However, low fluid more often indicates a leak somewhere. No matter why its low, symptoms are usually similar and can include:  

  • The brake pedal sinks lower to the floor than normal when applied. 
  • A spongy or inconsistent pedal feel. 
  • Longer stopping distances. 
  • A brake warning light is on. 
  • Pulling to one side when stopping. 

Simply knowing how to check brake fluid and topping it up can resolve some of these symptoms immediately. 

Checking the Brake Fluid 

When you’re testing brake fluid, what are you looking for? Primarily, ensure the brake fluid level is between the minimum and maximum lines on the reservoir. If it’s low, add fluid of the same type; you will see the specification stamped on the brake fluid reservoir cap. Secondly, check the condition. The fluid should be nearly clear or honey brown. If it’s dark brown or black, it’s overdue for a brake fluid flush. 

Where Is the Brake Fluid Located? 

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. 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 to check brake fluid, 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 the 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. 

Checking for Leaks 

If your reservoir was empty or close to it, there’s a great chance that you have a brake fluid leak. Inspect the brake system at every point to determine where the fluid is leaking from, then fix it right away. Applying pressure to the brake pedal while someone is watching the brake system can easily identify the area with a drip or spray from the problem area.  

Common Causes of Low Brake Fluid 

Low brake wear material is the most common cause of low fluid. Other issues that can cause the condition could be:  

  • A leaking brake caliper piston. 
  • A corroded or pinched steel brake line. 
  • A worn or cracked brake hose. 
  • A loose fitting or joint. 
  • Although rare, a seal leaking fluid from the master cylinder to the brake booster.

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. 

We Can Help

If you are 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 parts you need to restore your brakes and keep your vehicle operating safely. 

If you decide that it’s too big a job to tackle on your own, let AutoZone help you find qualified professional mechanics through our Shop Referral Program.  

Frequently Asked Question

How do I know if brake fluid is low? 

A visual inspection is the best method to confirm low brake fluid, although you may also notice declining brake operation or a brake warning light on. 

How do I check brake fluid level? 

To check the brake fluid level, open the hood and find the master cylinder reservoir. The level should be between the MIN and MAX indications on the side. 

Do you check brake fluid with the car running? 

The best practice is to check brake fluid when the vehicle is cold and the engine is off. 

Can you just add brake fluid to your car? 

You can simply add brake fluid if it’s low, however, it’s a good idea to inspect for leaks as well. 

Can I drive with low brake fluid? 

If the fluid is low but there is still some in the reservoir, it’s alright to drive your car a short time until you can add fluid. If there’s nothing in the reservoir, it’s not recommended to drive at all until it’s addressed. 

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