Brake Fluid Light On But Fluid Is Full – Troubleshooting Tips!

Brake fluid is essential for effective brake performance. Therefore, when it becomes too low, you will typically see a brake light on the dashboard warning you. 

So then, what causes the brake fluid to light on but the fluid is full? It could be due to a faulty sensor. Or the wiring harness to the brake fluid sensor could be damaged or shorted. If not, the parking brake could be partially engaged, a damaged master cylinder, or the brake pads worn.

But don’t fret! In this guide, you will discover how to diagnose and fix a brake fluid light when the fluid is full.

Causes and Fixes for Brake Fluid Light When Fluid Is Full

In a hurry? Find out why the brake light comes on when fluid is full and how to fix the problem in this quick guide.

Causes	Fixes
Faulty Brake Fluid Sensor	Replace the sensor
Partially Engaged Parking Brake	Adjust the parking brake cableReplace the cable Replace the calipers, brake pads, and shoes if worn
Damaged Wiring	Clean the corrosion on the wiring Replace the damaged wiresInstall new electrical connector
Faulty Master Cylinder	Install new master cylinder sealsReplace or rebuild the master cylinder
Brake Pads Being Worn	Replace the pads

Reasons for Brake Fluid Light On But Fluid Is Full

Typically, the brake fluid light will come on to alert you when the brake fluid is low. But what happens when it illuminates and the fluid is full? Read on to find out.

1. Faulty Brake Fluid Sensor

The brake fluid sensor is a switch that monitors the brake fluid level in the reservoir. You can find it submerged or floating inside your vehicle’s brake fluid.

Generally, the switch usually closes when the fluid levels become too low. However, sometimes, it may fail in a closed position, making the car think the fluid is low, yet it’s full. 

This happens when the float on the sensor loses buoyancy, causing it to sink at the threshold of the warning level. As a result, this causes the brake fluid light to come on.

Diagnosing and Fixing the Problem

1. Unplug the harness connector to the sensor. 
2. Then, test the two male pins or prongs that connect to the harness connector for continuity using a digital voltmeter.
3. If the fluid is filled, there should be no continuity. But if you get continuity, you must replace it.

Follow the steps to replace it:

Step 1: Disconnect the electrical connector to the sensor.

Step 2: Remove the old sensor.

Step 3: Install the new sensor by sliding it into the hole on the bottom of the brake master cylinder.

Step 4: Reconnect the electrical connector to the sensor.

2. Partially Engaged Parking Brake

If the parking or emergency brake is not fully released and the ignition is on, the brake fluid light may illuminate. This happens despite the brake fluid being full.

Generally, the parking brake may fail to disengage totally due to a corroded or misaligned cable. Worn brake pads, brake shoes, or calipers can also cause the parking brake to stay engaged slightly.

Diagnosing and Fixing the Problem

Pull the parking brake up and then put it down. If it does not disengage fully, apply and release the brakes several times. This can help dislodge rust or anything stuck on the parking brake cable. Otherwise, try the following;

1. Adjust the parking brake cable if it is misaligned.
2. Replace the parking brake cable if it is damaged.
3. Check the brake pads, caliper, and brake shoes for wear and replace them.

As for the brake pads, you should not change them yourself unless you are highly experienced. This is because if you are not careful, many things can go wrong during the replacement. Not to mention, the job is time-consuming.

With that said, to replace the brake calipers: 

• Step 1: Lift your car off the ground using a jack and secure it with jack stands.
• Step 2: Next, remove the lug nuts on the wheel with a damaged caliper using a wrench.
• Step 3: Remove the tire.
• Step 4: Place a drain pan under the caliper to catch any brake fluid.
• Step 5: Disconnect the brake line from the caliper and then plug using a brake hose plug.
• Step 6: Unfasten the caliper mounting bolts.
• Step 7: Pull the damaged caliper up and away from the rotor.
• Step 8: Install the new caliper in reverse order.
• Step 9: Refill the brake fluid and bleed the brakes to remove any air in the brake system.

If the brake shoes are also damaged, here is how to replace them:

• Step 1: Jack your car up and remove the tire to access the brake drum.
• Step 2: Unfasten the dust cap on the brake drum.
• Step 3: Next, remove the axle-bearing nut and bearing underneath the dust cover.
• Step 4: Remove the brake drum while twisting it.
• Step 5: Once you have removed the drum, remove all the brake shoe attachments. These include the retaining springs, washers, and pins.
• Step 6: Remove the old brake shoes and install the new ones in reverse order.

3. Damaged Wiring

The brake fluid sensor is connected to a wiring harness that comprises a collection of electrical wires. Over time, the wiring can become damaged, loose, or corroded, causing a short or open circuit. Consequently, this could trigger the brake fluid light.

Diagnosing and Fixing the Problem

Inspect the connectors of the wiring harness for corrosion and other signs of damage. 

Another way to diagnose damaged wiring is to test the wiring harness for continuity using a multimeter. If the multimeter does not beep, the wire is shorted. As such, you can repair it by:

1. Cutting the damaged section and splicing in a new wire
2. Alternatively, you can insulate the wire using electrical tape or
3. Replace the electrical connector if it is damaged

4. Faulty Master Cylinder

The brake master cylinder supplies hydraulic pressure to the brakes. However, the cylinder may fail over time due to wear and tear. And when it happens, your car may experience low brake fluid pressure, causing the brake fluid light to come on.

Diagnosing and Fixing the Problem

You can tell that the master cylinder is faulty if the brake pedal feels spongy or sinks when you pump the brakes.

Another way to make your diagnosis is by using a screwdriver. You simply press and hold the plunger in the rear of the cylinder using your screwdriver. If the plunger moves in, the master cylinder’s internal seals could be damaged.

So, to fix the problem:

1. Replace the damaged seals.
2. Rebuild the cylinder by replacing the piston, o-rings, and dust boot. You just need a master rebuild cylinder kit to help you replace and upgrade these components.
3. Install a new master cylinder if it has sustained damage.

Below is how to replace the master cylinder and the damaged seals:

• Step 1: Drain all the brake fluid from the reservoir.
• Step 2: Disconnect the brake fluid sensor connector from the master cylinder.
• Step 3: Loosen the brake lines that connect to the cylinder.
• Step 4: Unfasten the mounting bolts on the master cylinder. Then, remove the cylinder.
• Step 5: Next, remove the rear seal between the damaged master cylinder and brake booster. 
• Step 6: Install the new master cylinder with new seals in reverse order.
• Step 7: Add fresh brake fluid and bleed the brake system using a bleeder kit.

5. Brake Pads Being Worn

When the brake pads become worn significantly, a metal wire sensor is usually designed to press against the rotor. As a result, the brake fluid light may illuminate. This light can be accompanied by a brake pad indicator light, although this feature is not available in all car models.

If the brake pads are not replaced, they can cause the brake fluid to decrease over time.

Diagnosing and Fixing the Problem

Check for the brake pads’ wear indicator slot on the center of the pad. If the slot is not there or is barely noticeable, the pads are worn, and you must replace them.

Another way to diagnose the brake pads is to listen to the brakes when coming to a stop. If you hear squealing or clicking noises, replace the pads.

However, replacing brake pads is a job best left to professional mechanics. This is because the job requires a lot of tools, which you may not have. And if done incorrectly, you could compromise your safety. 

How To Reset Brake Fluid Light?

Sometimes, the brake fluid warning light may be triggered by a temporary glitch in the system. Therefore, the light may not go off even with the fluid being filled up and the sensors and wiring being okay. 

In this case, you can try resetting it by:

Step 1: Turn off the engine.

Step 2: Disconnect the negative battery terminal and then the positive cable.

Step 3: Reconnect the battery cables after 5 to 10 minutes.

Step 4: Start the engine and confirm if the light is gone.

If you have a BMW car, you can follow these steps to reset the brake fluid light. We have also included a short video for better understanding:

Step 1: Turn on the engine, but don’t start your car.

Step 2: Next, press the odometer reset button on the instrument cluster.

Step 3: Hold the button until the service menu appears. Then, toggle through the various options until the brake fluid warning symbol appears.

Step 4: Once the light appears, stop toggling. Then, press the odometer reset button and hold it.

Step 5: Release the button once you see reset at the bottom of the brake fluid symbol. Then, press it again. The color of the light should change from red to orange to confirm it has been reset. 

While ensuring the brake fluid is at its optimal level is crucial, there are other indicators and warnings that might arise in your vehicle’s system. If you ever encounter a situation where the brake light on your dashboard intermittently illuminates, our comprehensive guide can provide insights into potential causes. In another scenario, you might find it perplexing when the oil light turns on specifically when you apply the brakes. Being informed about these diverse symptoms can assist in maintaining your vehicle’s efficiency and ensuring safety during drives.

FAQs

Before we conclude, we will quickly respond to commonly asked questions about brake fluid lights on.

Bottom Line

If the fluid is full in the reservoir, but the brake fluid light is on, you should not ignore the warning. This is because the brake pads could be worn, the brake fluid sensor could be damaged, or the master cylinder could be faulty. 

Therefore, if you don’t diagnose and fix the problem, you could experience complete brake system failure. With that said, knowing how to reset the warning light is equally important. This is because sometimes the light can be falsely triggered despite all the brake components being in good condition.