Brake/Park Brake Indicator

The brake indicator gives an indication to the vehicle operator when the parking brake is applied, when there are certain brake hydraulic system malfunctions as indicated by a low brake hydraulic fluid level condition or when the brake fluid level switch is disconnected. The brake indicator can also give an indication when certain faults are detected in the Antilock Brake System (ABS). This indicator is controlled by a transistor on the IC circuit board based upon programming and electronic messages received by the IC from the CAB or the Body Control Module (BCM) over the CAN data bus. The BCM monitors the hard wired input from the park brake switch. The IC will illuminate the brake indicator for about three seconds as a bulb test each time the ignition switch status transitions to ON.

The brake indicator LED is completely controlled by the IC logic circuit, and that logic will only allow this indicator to operate when the IC receives a battery current input on the fused ignition output (run-start) circuit. Therefore, the LED will always be OFF when the ignition switch status anything except ON or START. The LED only illuminates when it is provided a path to ground by the IC transistor. The IC will turn ON the brake indicator for the following reasons:

• Brake Indicator Lamp-On Message  - Each time the IC receives an electronic brake indicator lamp-ON  message from the CAB, the brake indicator will be illuminated. The CAB may also send lamp-ON messages as feedback during ABS diagnostic procedures. The indicator remains illuminated until the IC receives a lamp-OFF message from the CAB or until the ignition switch status transitions to OFF, whichever occurs first.
• Low Brake Fluid Textual Warning Message  - When the CAB detects a low brake fluid level input from the brake fluid level switch, it will send an electronic textual warning request  message requesting the IC display a textual warning message. Each time the IC receives this message from the CAB, a LOW BRAKE FLUID LEVEL  textual message will appear within the IC electronic display to accompany brake indicator illumination. This message indicates that the CAB has detected a low brake fluid level condition in the brake master cylinder or that there is a problem in the brake fluid level switch or circuits.
• Park Brake Switch Input  - Each time the IC receives an electronic brake indicator lamp-FLASH  message from the BCM, the brake indicator will be flashed ON and OFF. While the ignition switch status is ON, the BCM monitors the park brake switch through the park brake switch sense circuit (park brake switch closed = park brake applied or not fully released). The indicator continues to flash until the park brake switch sense input to the BCM is an open circuit (park brake switch open = park brake fully released), or until the ignition switch status transitions to OFF, whichever occurs first.
• Antilock Brake System (ABS) Indicator Backup  - If the IC detects a fault in the ABS indicator circuit it will send a message indicating the fault to the CAB, then flash the brake indicator ON and OFF. The IC will continue to flash the brake indicator until the ABS indicator circuit fault is resolved, or until the ignition switch status transitions to OFF, whichever occurs first.

The park brake switch on the park brake lever mechanism provides a hard-wired ground input to the BCM circuitry through the park brake switch sense circuit whenever the park brake is applied or not fully released. The CAB continually monitors the ABS system circuits and sensors, including the brake fluid level switch on the brake master cylinder reservoir, to decide whether the system is in good operating condition. The CAB then sends the proper lamp-ON, lamp-OFF or lamp-FLASH message to the IC. If the CAB sends a lamp-ON message after the bulb test, it indicates that the CAB has detected a brake hydraulic system malfunction or that the ABS system has become ineffective. The CAB will store a DTC for any malfunction it detects.

The hard wired park brake switch input to the BCM may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. For proper diagnosis of the brake fluid level switch, the ABS, the BCM, the CAB, the IC, the CAN data bus or the electronic communication related to brake indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.