Brake Pad Wear Indicator
Electronic sensors provide a warning light for the driver when the brake pads have worn past a specified limit. They replace an audible metal clip that's fastened to the brake pad. When the pad wears down to the clip, a loud squeal is heard when the brakes are applied.
The electric pad warning system is a less intrusive way of indicating pad wear to the driver. When this wired circuit is interrupted, the pad wear warning light illuminates on the instrument panel.
Unfortunately, by the time the driver's light comes on, the sensor's circuit has already been broken, requiring sensor replacement. Test these sensors for resistance with an ohmmeter.
Many brake pad manufacturers have cut a slot into the middle of the pad that acts as a wear indicator. The slot cools the pad surface as air passes through the groove. It also helps remove brake dust and allows gas to escape.