Brake Indicator: Operation

WARNING: This page is about a different car, the 2006 Dodge Sprinter. However, it is still accessible from the selected car via links, so may be relevant.

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 BODY DIAGNOSTIC PROCEDURES .