Why Is My Brake Light On? (5 Reasons)

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This isn’t as uncommon as you think, starting up the car or driving and discovering your vehicle’s brake light is on, but why is my brake light on?

There are numerous reasons the brake light on the dash can illuminate from the handbrake not wholly disengaged, the brake fluid is low, the brake pad wear sensor is grounded, ABS module failure, and electric parking brake failure.

Now let us go through what to do when the brake light comes on.

parking brake anti lock brake and brake warning light

5 Reasons Why Is My Brake Light On?

For your safety when driving and the brake light is illuminated on the dash, find the closest safest spot to diagnose the problem while your brakes are still functioning.

1. Parking Brake Isn’t Fully Disengaged

It happens to everyone who has driven a car with a manual parking brake that you accidentally didn’t disengage.

Only the brake light will be on in older vehicles as a warning that you are driving with the parking brake engaged.

Newer vehicles are installed with a warning chime and a warning light to get your attention if the parking brake is engaged.

2. Electric Parking Brake Failure

On higher-end vehicles, you won’t find the conventional parking brake engaged by pulling it with your hands or pushing it with your feet but with a little rocker switch.

The electric parking brake has a little motor installed underneath the car that either pulls the parking brake cables or pressurizes the brake lines to ensure the vehicle does not move when engaged.

When a fault is detected, or the motor has broken, this will illuminate the brake warning light on the dash.

3. Brake Fluid Is Low

Once you are parked in a safe area, you can open the car’s hood and search around the firewall on the driver’s side; you will find the brake fluid reservoir there.

Inspect the brake fluid reservoir; if the brake fluid is below the low indicator, the brake warning light will come on.

There are two reasons that the brake fluid has depleted.

The first reason is that the brake pads and discs have worn down because the further the brake caliper pistons and drum brake pistons have to move out, the more fluid is used to keep them there.

In this scenario, you need to inspect the brake pads to see how much life they have left.

Usually, you will hear the brake wear indicators on the pads before the brake fluid becomes an issue to inform you the pads needs replacement.

If the pads are worn out, you can temporarily put in more brake fluid, but you will need to replace the brake pads as soon as possible.

If the brake pads have enough life, there is a bigger problem, which is reason number 2; a brake fluid leak.

Inspect the ground underneath the car to see any visible puddles, or look at the undercarriage to see if there is any wet, oily substance on it.

If you find a leak next to the road, do not drive further with the vehicle since the brakes will lose effectiveness until it ultimately doesn’t work.

4. Brake Pad Wear Sensor Is Grounded

While some cars have little metal plates that are used to indicate the pads are worn down audibly, other vehicles might use a brake pad wear sensor.

The sensor is just an open circuit, and the only way for the circuit to close is for the brake pad to wear down far enough so that the sensor will either come in contact with the brake pad backing plate or the brake rotor itself.

Once the sensor grounds itself on something metal, the brake light will illuminate.

These sensors are known to degrade over time and break off at the connector, so inspect the wiring if you see that the sensor is not touching anything.

You will need to replace the brake pads and the censors if it is touching.

5. ABS Module Failure

The job of the ABS module is to regulate the pressure on each brake on the car to ensure that the wheels don’t lock up under emergency braking.

If there is any fault on the inside of the module, distribution block, or speed censors on the wheels, the brake light will come on the dash.

You or a mechanic should perform a vehicle diagnostic with an OBD (On Board Diagnostic) scanner to find the fault since everything that can go wrong here is electronic.

brake fluid reservoir
A generic brake fluid reservoir with the correct symbols to indicate it is for the brake system.

Final Thoughts On Why My Brake Light Is On

It is concerning when the one thing that can bring your car to a stop has a problem, and that is the braking system.

Even if it is something small, like the fluid just being low or the brake wear sensor that has shorted out, it should be addressed so the warning light can illuminate if there is a bigger problem.

Hopefully, you found this article informative, and it will help keep you driving many miles safely.


What Happens If The Brake Fluid Is Low?

When there is too little brake fluid in the reservoir, the chances are very high that the master cylinder can draw in air when you use the brakes.
Air can be very easily compressed compared to a fluid resulting in your brake pedal feeling spongy and the brakes unresponsive.

Can I Top Up Brake Fluid Myself?

Yes, it is one of the most straightforward jobs you can do yourself on your vehicle.
Make sure to put the fluid in the correct reservoir; it is usually against the firewall in the engine bay on the driver’s side, and use the correct DOT-approved fluid.

How Often Should I Top Up My Brake Fluid?

To top up when the brake light comes on due to too little fluid in the reservoir.
Suppose you have driven for two years without topping up the brake fluid. 
In that case, it is recommended by most manufacturers to replace the fluid in the whole system.
The reason for this is that over time the brake fluid gets contaminated, resulting in the boiling point of the fluid to lower, causing it to boil under braking and cause spongy brakes and bad brake performance.