Brake Wear Indicator

BRAKE WEAR INDICATOR

DESCRIPTION
A brake wear indicator is standard equipment on all instrument clusters. The brake wear indicator is located near the lower edge of the instrument cluster, to the left of the multi-function indicator display. The brake wear indicator consists of the International Control and Display Symbol icon for "Worn Brake Linings" imprinted within a rectangular cutout in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. An amber Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the icon to appear silhouetted against an amber field through the translucent outer layer of the overlay when the indicator is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic circuit board. The brake wear indicator is serviced as a unit with the instrument cluster.

OPERATION
The brake wear indicator gives an indication to the vehicle operator when the brake linings have reached their wear limits. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and a hard wired input from the four brake wear sensors, one at each wheel. The brake wear indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster detects that the ignition switch is in the On position. Therefore, the LED will always be off when the ignition switch is in any position except On. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn on the brake wear indicator for the following reasons:
- Bulb Test - Each time the ignition switch is turned to the On position the brake wear indicator is illuminated by the instrument cluster for about two seconds as a bulb test.
- Brake Wear Sensor Input - Each time the cluster detects ground on the brake wear sense circuit (brake wear sensor closed = brake lining wear limit exceeded) while the ignition switch is in the On position, the brake wear indicator is illuminated. The indicator remains illuminated until the brake wear sense input to the cluster is an open circuit (brake wear sensor open = brake lining wear within limits), or until the ignition switch is turned to the Off position, whichever occurs first.

A brake wear sensor located at each wheel provides a hard wired ground input to the instrument cluster circuitry through the brake wear sense circuit whenever the brake linings for that wheel have exceeded their wear limits. The four normally open brake wear sensors are connected in parallel between ground and instrument cluster. The brake wear sensors and their input circuit to the instrument cluster can be diagnosed using conventional diagnostic tools and methods. For proper diagnosis of the instrument cluster circuitry that controls the brake wear indicator, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.