Before replacing a caliper, a few simple tests confirm whether it is actually the problem. You do not need special equipment for most of them. Here is how to test a brake caliper for the common faults.
The hot-wheel test
After a short drive (no hard braking), carefully feel each wheel. A caliper that is dragging keeps its wheel and rotor much hotter than the others - a classic sign of a sticking caliper; see sticking caliper symptoms. A big temperature difference between sides points to the hot corner.
Read the pad wear
Pull the wheel and compare pad wear. A caliper problem shows as one pad far more worn than its partner, or one side of the car worn more than the other; see reading pad wear patterns. Even, matched wear means the caliper is doing its job.
Check the pins and piston
With the caliper off, the slide pins should move freely and smoothly - seized pins mean it cannot float; see caliper won't retract. The piston should compress smoothly with a tool (opening the bleeder first). A piston that will not budge or is rusted is failing.
Look for leaks
Inspect for wet fluid around the piston boot, bleeder, and hose - any weeping means a leaking caliper. If the pins are free, the piston moves, there is no leak, and the wheel is not dragging, the caliper is likely fine - look elsewhere. When a caliper does fail, replace it and fit fresh pads and hardware.