Why does the brake fluid warning light come on?

The brake fluid warning light in your vehicle is an important indicator that something may be wrong with your braking system. This light typically illuminates when the brake fluid level in the master cylinder is low, signaling the need for immediate attention to prevent potential brake failure.

What Causes the Brake Fluid Warning Light to Illuminate?

There are several common reasons why the brake fluid warning light may come on in your vehicle:

• Low Brake Fluid Level: The most common cause is a low level of brake fluid in the master cylinder. This can happen due to normal wear and tear, a leak in the brake system, or even just from the brake pads wearing down over time.


• Brake Fluid Leak: A leak in the brake lines, calipers, or other components of the braking system can cause the fluid level to drop, triggering the warning light.


• Worn Brake Pads: As brake pads wear down, they require more brake fluid to maintain proper pressure in the system. This can cause the fluid level to drop and the warning light to illuminate.


• Contaminated Brake Fluid: Over time, brake fluid can become contaminated with moisture or other impurities, reducing its effectiveness. This can also cause the warning light to come on.

It's important to address the underlying issue as soon as the brake fluid warning light comes on to ensure the safety and proper functioning of your vehicle's braking system.

How to Respond to the Brake Fluid Warning Light

If the brake fluid warning light illuminates, you should take the following steps:

• Check the Brake Fluid Level: Locate the brake fluid reservoir, usually under the hood, and check the fluid level. If it's low, top it up with the recommended brake fluid type.


• Inspect for Leaks: Carefully inspect the brake lines, calipers, and other components for any signs of fluid leaks. If you find a leak, have it repaired by a qualified mechanic as soon as possible.


• Have the System Inspected: If the fluid level is normal and there are no visible leaks, the issue may be more complex, such as a problem with the brake fluid itself or a deeper issue in the braking system. Have a mechanic inspect the system to diagnose and address the problem.

Ignoring the brake fluid warning light can lead to further damage to your vehicle's braking system and potentially dangerous driving conditions. It's crucial to address the issue promptly to ensure the safety of you and your passengers.

How much does it cost to replace a brake fluid sensor?

The cost to replace a brake fluid sensor varies, but you can expect to pay $20 to $100 for the part itself and an additional $100 to $300 or more for professional installation, depending on the vehicle and labor rates. For a simple DIY replacement, the cost is generally lower, ranging from around $20 to $100 for the part alone, JustAnswer reports. 
You can watch this video to learn about the brake fluid level sensor: 12sNGK Spark Plugs USAYouTube · Jul 20, 2018
Cost breakdown

• Parts: Brake fluid level sensors typically cost between $20 and $100. Some types, like brake booster pressure sensors, can cost more, ranging from $100 to $300 or more for the part and labor combined. 
• Labor: If you have a mechanic do the work, labor costs can significantly increase the total. This is especially true for more complex sensors or if the job requires additional work. 
• DIY vs. Professional:
  • DIY: You can save on labor costs by replacing the sensor yourself, but you'll need to purchase the part (around $20-$100). 
  • Professional: For a total cost between $100 and $300 or more, including parts and labor, a professional mechanic is the most convenient option. 

Factors that affect cost

• Vehicle Make and Model: The cost of the sensor and the labor needed to replace it can vary depending on your vehicle's make and model. 
• Type of Sensor: There are different types of brake sensors, including level, pressure, and booster sensors. Each type has a different cost structure. 
• Labor Rates: Labor costs vary by location, so getting a quote from different mechanics can help you find a competitive price. 

Tips for saving money

• DIY: If you are comfortable with basic car maintenance, consider replacing the sensor yourself to save on labor costs. 
• Shop around: Compare prices for the part and labor at different auto parts stores and mechanics before making a decision.
• Check for promotions: Some auto parts stores offer discounts on parts or installation services, so keep an eye out for sales and promotions. 
• Replace in pairs: If one sensor is failing, it's often recommended to replace all sensors in the system, especially if they are old or worn out. 

Why does my car say low brake fluid when it's full?

A "low brake fluid" warning with a full reservoir is often caused by a faulty level sensor or worn brake pads, which require more fluid to push the brake calipers against the rotors. Less commonly, the fluid level might appear low due to internal leaks into the brake booster or the fluid itself may have become contaminated or absorbed moisture. A visual inspection of the brake pads and professional diagnosis can help determine the exact cause. 
This video explains why the brake fluid level might appear low even when the reservoir is full: 57sThe Pit Stop Tire ProsYouTube · Jan 25, 2021
Common reasons for the warning

• Worn brake pads: As brake pads wear down, the caliper pistons extend further. This movement requires more brake fluid to fill the increased space, causing the level in the reservoir to drop. 
• Faulty sensor: The warning light is triggered by a sensor in the reservoir. This sensor can malfunction, be dirty, have a corroded wire, or be dislodged by a vehicle's movement on a hill or a sharp turn. 
• Internal leaks: A leak may not be visible on the ground if it's internal. Brake fluid can leak into the brake booster or other components, causing the reservoir level to drop. 
• Moisture or contamination: Over time, brake fluid can absorb moisture or become contaminated with dirt. This can reduce its effectiveness and may damage the sensor over time. 

This video demonstrates how to check brake fluid levels and identify potential issues: 1mFord Boss Me - Auto / Politics / Family YouTube · Nov 20, 2021
What to do

• Inspect brake pads: Visually check the thickness of your brake pads. If they are thin, they will need to be replaced soon. 
• Check the sensor: Examine the brake fluid reservoir for any signs of corrosion or a loose wire. 
• Have the system inspected: Take the car to a mechanic to check for leaks, proper brake pad thickness, and to have the fluid flushed and replaced if necessary. 

This video explains the function of the brake fluid level sensor and how it can fail: 35sAuto Repair GuysYouTube · Feb 17, 2021

Can I add brake fluid to my car myself?

Yes, you can add brake fluid yourself if the level is low, but if the level dropped significantly, it may indicate worn brake pads or a leak and require further inspection. To top it off, locate the brake fluid reservoir, clean the area around the cap, and slowly pour the correct type of brake fluid up to the "MAX" line. Be careful not to spill any, as it can damage car paint. 
What to do if you need to add brake fluid

1. Check your owner's manual: Determine the correct type of brake fluid your car needs, such as DOT 3 or DOT 4. The type is often marked on the reservoir cap. 
2. Locate the reservoir: Find the brake fluid reservoir, which is usually a translucent plastic container in the engine bay, often on the driver's side. 
3. Clean the area: Wipe down the reservoir and the cap with a clean rag to prevent dirt and moisture from entering the system. 
4. Check the fluid level: Look at the "MIN" and "MAX" lines on the side of the reservoir. If the fluid is at or above "MIN," you don't need to add any. 
5. Add fluid: If the fluid is low, carefully remove the cap. Use a funnel to avoid spills and slowly pour the new brake fluid into the reservoir until it reaches the "MAX" line. Do not overfill. 
6. Secure the cap: Put the cap back on tightly to prevent air and moisture from entering the system. 
7. Clean any spills immediately: Wipe up any spilled fluid right away, as it can damage paint. 

You can watch this video to learn how to add brake fluid to your car: 59sEvansHalshawTVYouTube · Jun 23, 2023
When to seek professional help

• If you are adding fluid frequently: If you consistently need to add brake fluid, your brake pads are likely worn down, or there is a leak in the system. 
• If the brakes feel spongy: If the brake pedal feels soft or spongy, air may have entered the brake lines, which requires the system to be bled. 
• If the fluid is very dark: If the old fluid is dark or murky, it needs to be completely flushed and replaced, which is a more involved process that may be best left to a professional, especially on modern vehicles with complex ABS systems. 

Can I drive my car with the brake fluid light on?

If your brake fluid is low, top it up with the recommended type of brake fluid. If the brake light remains illuminated even after inspecting the brake fluid, it is advisable to safely manoeuvre your vehicle to the side of the road. Employ your indicator and gradually decrease your speed.