Brake Indicator

BRAKE INDICATOR

DESCRIPTION
A brake indicator is standard equipment on all instrument clusters. The brake indicator is located near the lower edge of the instrument cluster, to the left of the multi-function indicator display. In vehicles built for the United States market, the brake indicator consists of a stencil-like cutout of the word "BRAKE" in the opaque layer of the instrument cluster overlay. In vehicles built for the Canadian market, the brake indicator consists of the International Control and Display Symbol icon for "Brake Failure" imprinted within a rectangular cutout in the opaque layer of the instrument cluster overlay. In either case, the dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. A red Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the "BRAKE" text to appear in red, or the icon to appear silhouetted against a red 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 indicator is serviced as a unit with the instrument cluster.

OPERATION
The brake indicator gives an indication to the vehicle operator when there are certain brake hydraulic system malfunctions as indicated by a low brake hydraulic fluid level condition, or when there is a problem in the electronic brake force distribution (EBV) system. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming, electronic messages received by the cluster from the Controller Antilock Brake (CAB) over the Controller Area Network (CAN) data bus, and a hard wired input from the brake fluid level switch. The brake 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 indicator for the following reasons:

- Bulb Test - Each time the ignition switch is turned to the On position the brake indicator is illuminated by the instrument cluster for about two seconds as a bulb test.
- Brake Fluid Level Switch Input - Each time the cluster detects ground on the brake indicator signal circuit (brake fluid level switch closed = brake fluid level low) while the ignition switch is in the On position, the brake indicator is illuminated. The indicator remains illuminated until the brake signal indicator input to the cluster is an open circuit (brake fluid level switch open = brake fluid level okay), or until the ignition switch is turned to the Off position, whichever occurs first.
- Electronic Brake Force Distribution (EBV) Indicator Lamp-On Message - Each time the cluster receives a EBV indicator lamp-on message from the CAB, the indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-off message from the CAB, or until the ignition switch is turned to the Off position, whichever occurs first.

The CAB continually monitors the EBV system circuits and sensors to decide whether the system is in good operating condition. The CAB then sends the proper lamp-on or lamp-off messages to the instrument cluster. If the CAB sends a lamp-on message after the bulb test, it indicates that the CAB has detected a system malfunction and that the EBV system has become inoperative. The CAB will store a Diagnostic Trouble Code (DTC) for any malfunction it detects.

The brake fluid level switch in the brake master cylinder provides a hard wired ground input to the instrument cluster circuitry through the brake indicator signal circuit whenever the fluid level in the brake master cylinder is low. The switch is connected in parallel between ground and the instrument cluster. The brake fluid level switch and the 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 indicator, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.