1. The brake fluid reservoir is low. When you replace the brake pads, you need to add brake fluid to the reservoir to compensate for the fluid that was lost when you removed the old pads. If the reservoir is low, there won't be enough fluid to create the pressure needed to move the brake pistons and engage the brakes.
Check the brake fluid level and add more if necessary. The reservoir is located under the hood, near the master cylinder. It's a clear plastic container with a black cap. The fluid level should be between the "Min" and "Max" marks on the side of the reservoir.
2. There is air in the brake lines. When you replace the brake pads, it's possible for air to get into the brake lines. Air bubbles can compress, which will reduce the pressure in the brake lines and make it difficult to engage the brakes.
To remove the air from the brake lines, you need to bleed the brakes. Bleeding the brakes involves opening a bleeder screw on each brake caliper and allowing the air to escape. You will need a brake bleeder kit to do this.
3. The brake pads are not properly seated. If the brake pads are not properly seated, they won't be able to make contact with the rotors and stop the car.
Make sure that the brake pads are seated properly in the calipers. The pads should be flush with the rotors and there should be no gap between the pads and the rotors.
4. The brake calipers are seized. If the brake calipers are seized, they won't be able to move the brake pads and engage the brakes.
Try to move the brake calipers by hand. If they don't move, they are seized. You will need to replace the brake calipers.
If you have tried all of these things and you still don't have a brake pedal, you should take your car to a mechanic. There may be a more serious problem with the brakes that you are not aware of.
