Brake Pad Wear Sensors

A brake pad wear sensor tells the driver when the pads are close to their minimum thickness. It is a short wire with a sensing head that clips into the pad, and a plug that joins the car’s wiring. Sensors here are listed for the front or rear axle, by reference code.

Most sensors carry a wire loop inside a plastic head that sits at a set depth in the friction material. When the pad wears down to that depth, the disc grinds through the loop, the circuit opens and a warning lamp or message appears. Other designs use a single wire that warns when it touches the disc, which is one reason sensors are matched to the car rather than to the pad.

A triggered loop sensor is cut through and cannot reset, so it has to be replaced. Even one that has not triggered is often renewed with the pads, as heat makes the head brittle and removal can break it or its clip.

Points to check when ordering:

• Axle: front and rear sensors usually differ in wire length and sometimes in plug, so they are not interchangeable.
• Reference code: each sensor is identified by the code that opens its title. Compare it with the car’s listing and with the part you remove.
• Number per car: many cars have one sensor per axle on a single wheel, others one per wheel, so count before ordering.
• Pad compatibility: performance pads need a slot or clip for the sensor head. Check that before ordering pads and sensors together.

Press the head fully into its slot so it reads at the depth it was designed for. Route the wire through its original clips and grommets, clear of the disc, wheel and moving suspension parts, then check it at full steering lock and full droop. A trapped or chafed wire can give a false warning, or none at all.

Fit sensors as part of an axle set of pads, and reset any service reminder the car links to them. On a track car the sensor is a backstop, not a gauge: it warns at one fixed point, so check pad thickness by eye at every event.