Download Vehicles with ETS, ESP or ASR have wear sensors for the brake pad wear indicator on the rear axle. There are the following versions: No sensor 2 sensors 4 sensors There are the following versions on the front axle: 2 sensors 4 sensors. When replacing brake pads only install as many sensors as were fitted originally. if only one wear sensor is fitted to a wheel, it is to be fitted to the outer brake pad. Wear sensors which are not connected result in the brake pad wear malfunction indicator lamp coming on due to moisture. NOTE The wear sensor cable must be routed as shown in the illustration. Only the transparent (temperature-resistant) version of the wear sensors may be installed on the rear axle.