A brake caliper contains one or more pistons, depending upon the type of caliper. The pistons move inside of cylinders due to buildup of brake fluid pressure that is delivered via brake lines and flexible hoses. The pistons press outward onto the brake pads, which forces the brake pads to press against the brake discs.
The most common problems with the brake caliper is that the pistons can seize up, or the seals that are on the pistons can begin to leak. When either of these problems occur, then the brake caliper will fail to work correctly and they will need replacing.
Most manufacturer factory warranties will cover a brake caliper under the bumper-to-bumper warranty section of the factory warranty. For extended coverage of a brake caliper after the factory warranty has expired, an extended auto warranty is an option.