I have a 2016 explorer. I noticed weird noise coming from my brakes. I took off the front caliper and noticed something weird. I'm not sure if it's normal or not. I noticed the caliper had two pistons. I stepped on the brakes and noticed that only one piston came out forward while the other pistons stayed back. Is that normal for only one piston to press the brake pads? or are both pistons supposed to press the brake pad?
You are correct in thinking there is something wrong with pistons. When the pedal is applied, the piston should come out and apply the brake pads evenly. Check the brake pads themselves for uneven wear. If the braking material tappers off, you know that only one side of the brake is working. This may also mean that half of the brake pad is applying itself while the brakes should be released.
Make sure you know the difference between the piston and the guide pins. Guide pins allow the caliper to move back and forth freely. There are also two of these. If the guide pins are sticking, you will have very similar symptoms. Guide pins will need to be re-greased if they become dirty or dry.