How can I tell if my brakes need to be replaced?

One of the things that can cause the squeaking is a layer of brake dust between the piston in the caliper and the back of the brake pad. This can be remedied by pulling the caliper off and cleaning the piston and the back of the pad with a wire brush. There is some no-squeal goo that big box parts stores sell that can be applied to the piston before reassembly. It will delay the return of the problem.

Since you have to pull the wheel off to do this, inspect BOTH sides of each rotor. Most often I find the problem on the inside surface. If there is scoring on the rotor, you have the more serious problem that others have described. If you do the work yourself, it isn't too expensive.

I had a similar problem with a Caravan that was solved with new pads and rotors. I think the Chinese sourced rotors were something like $24.00 each and gave good service until I sold the vehicle about 35k miles later.