The ONLY way to check brake pads is to look at them. The OEM pads have a inspection "groove" cut in them. If the pad is worn beyond this groove, it's time to replace them. You need to get down on the garage floor and twist yourself around like a pretzel. A mirror and light will be most helpful. Fine a friend that knows how to check them and have him show you. If they need changing, and you have any mechanical knowledge, it's an easy change. I am a mechanical dumb a$$ and had all three sets of pads changed in less than an hour.