Why does the brake pedal go down when the engine starts

When you start your car, you may notice that the brake pedal goes down slightly. This is because the power brake booster, which assists you in braking, is activating. The booster uses vacuum from the engine to create additional force when you press the pedal, making it easier to stop your car.

When the engine is off, there is no vacuum, so the booster cannot assist you. This means that you will need to apply more force to the brake pedal to stop your car.

Here are some additional reasons why the brake pedal may go down when the engine starts:

Air in the brake lines: If there is air in the brake lines, it can cause the brake pedal to go down when the engine starts. This is because air is compressible, so it can absorb some of the force that you apply to the pedal.
Leaking brake master cylinder: A leaking brake master cylinder can also cause the brake pedal to go down when the engine starts. This is because the master cylinder is responsible for sending brake fluid to the calipers and wheel cylinders, and if it is leaking, it can cause the brake fluid level to drop.
Worn brake pads: Worn brake pads can also cause the brake pedal to go down when the engine starts. This is because the brake pads are what actually stop your car, and if they are worn, they will not be able to provide as much friction.

Why does my brake pedal go down all the way to the floor? This could be a sign of a leak in the brake system.
Why does my brake pedal feel spongy? This could be a sign of air in the brake lines.
Why does my brake pedal pulsate? This could be a sign of warped brake rotors.
Why does my brake pedal squeak? This could be a sign of worn brake pads.
Why does my brake pedal vibrate? This could be a sign of a problem with the brake calipers.

Brake Pads by [Brand Name]
Brake Rotors by [Brand Name]
Brake Calipers by [Brand Name]
Brake Master Cylinder by [Brand Name]
Brake Lines by [Brand Name]

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Why does the brake pedal go down when the engine starts?

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