Brake pads, rotors, and brake fluid are all crucial components of a vehicle's braking system. They work together to slow down and stop the vehicle when the brakes are applied. Here are some reasons why they need to be checked and replaced:

1. Brake pads: Brake pads are the part of the braking system that actually makes contact with the rotor to slow the vehicle down. Over time, the friction material on the pads wears down, reducing their ability to stop the vehicle effectively. Worn brake pads can also damage the rotor and lead to more expensive repairs. Therefore, it's important to have the brake pads checked regularly and replaced as needed.

2. Rotors: The rotors are the flat, round discs that the brake pads press against to slow down the vehicle. Like brake pads, rotors can become worn over time, which can affect the braking performance of the vehicle. In some cases, rotors can also become warped or cracked, which can cause shaking or vibration when the brakes are applied. In such cases, the rotors need to be replaced to ensure the safe operation of the vehicle.

3. Brake fluid: Brake fluid is the hydraulic fluid that transfers the force from the brake pedal to the brake calipers, which then squeeze the brake pads onto the rotors to slow the vehicle down. Over time, brake fluid can become contaminated with moisture and other contaminants, which can cause it to break down and become less effective. When this happens, the braking performance of the vehicle can be compromised. Therefore, it's important to have the brake fluid checked regularly and replaced as needed.

In summary, regular inspection and replacement of brake pads, rotors, and brake fluid are essential to maintain the safe and effective operation of a vehicle's braking system.