* Rust or corrosion on the piston or in the caliper bore: Rust or corrosion can cause the piston to stick in the bore and prevent it from compressing.
* Dirt or debris in the caliper bore: Dirt or debris can also cause the piston to stick in the bore and prevent it from compressing.
* A damaged or defective brake caliper: If the brake caliper is damaged or defective, it may not be able to compress the piston properly.
* A problem with the brake fluid: If the brake fluid is old or contaminated, it can cause the caliper piston to stick and prevent it from compressing.
If you are unable to compress the brake caliper piston, you should take your vehicle to a qualified mechanic to have it inspected and repaired.
