[KTL]

-Pull both brake pads out of only one caliper.
-Press the brake pedal down about 1/2 way.
-Go look at the caliper and see how the pistons moved.
-If both extended out of the caliper somewhat evenly, without much pressure needed at the brake pedal? That caliper is fine. You may need to press the pedal a few times 1/2 way to get the pistons to retract a noticeable amount. This is especially the case for the front brakes where the larger pistons move less. Be sure to only press the brake pedal 1/2 way (it's very easy to floor the pedal) so you don't overextend the travel of the master cylinder- overextension sometimes causes the master to fail.
-Push pistons back into caliper and reinstall brake pads.
-Press brake pedal until pads press against recently worked on caliper.
-Go to next caliper and repeat the procedure.
-If you run into a caliper that has a piston(s) that don't want to come out? You've got a booged up piston that needs to be removed and cleaned or replaced. Possibly could need a replacement caliper dependent upon level of corrosion.

Before testing the calipers, test the master cylinder by pumping the pedal and holding the pedal down very firmly for at least 20 seconds. If you notice the pedal slowly dropping as you apply firm pressure? You've got a failed master cylinder that needs to be replaced.