Brake Pad Wear Sensor
An electronic or mechanical sensor that alerts the driver when the brake pads have worn thin.
A brake pad wear sensor is a safety device designed to alert the driver when the brake pad friction material has worn down to a critical thickness, indicating that a brake service is required. There are two main types of wear indicators: mechanical scratchers and electronic sensors.
A mechanical wear indicator is a simple metal tab attached to the brake pad backing plate. When the pad wears down to about 2 millimeters, the metal tab makes contact with the spinning brake rotor, producing a loud, high-pitched squealing or chirping noise when driving or braking, warning the driver that the pads are thin.
An electronic wear sensor (common on European and luxury vehicles) is a small wire loop embedded in the brake pad friction material. When the pad wears down, the wire makes contact with the rotor, completing or breaking an electrical circuit. This triggers a warning message or icon on the dashboard instrument cluster. Most electronic sensors are single-use and melt when triggered, meaning they must be replaced along with the new brake pads.
Regularly inspecting brake pads and replacing them when the wear indicators trigger prevents metal-on-metal contact, which can rapidly score and ruin the more expensive brake rotors and calipers.