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 IPC circuit board based upon IPC programming, electronic messages received by the IPC from the ABS module over the CAN data bus, and a hard-wired input from the park brake switch.

The brake indicator LED is completely controlled by the IPC logic circuit, and that logic will only allow this indicator to operate when the IPC receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED will always be OFF when the ignition switch is in any position except ON or START. The LED only illuminates when it is provided a path to ground by the IPC transistor. Each time the ignition switch is turned to the ON position the brake indicator is illuminated by the IPC for about three seconds as a bulb test. The IPC will turn ON the brake indicator for the following reasons:

• Brake Indicator Lamp-On Message  - Each time the IPC receives an electronic brake indicator lamp-ON  message from the ABS module, the brake indicator will be illuminated. The ABS module may also send lamp-ON messages as feedback during ABS diagnostic procedures. The indicator remains illuminated until the IPC receives a lamp-OFF message from the ABS module, or until the ignition switch is turned to the OFF position, whichever occurs first.
• Park Brake Switch Input  - Each time the IPC detects ground on the park brake switch sense circuit (park brake switch closed = park brake applied or not fully released) while the ignition switch is in the ON position, and the gear position changes from the park position, the brake indicator flashes ON and OFF. The indicator continues to flash until the park brake switch sense input to the IPC is an open circuit (park brake switch open = park brake fully released), or until the ignition switch is turned to the OFF position, whichever occurs first. If the park brake is not fully released, and the vehicle is moving at 8 mph, the chime will sound.
• Antilock Brake System (ABS) Indicator Backup  - If the IPC detects a fault in the ABS indicator circuit it will send a message indicating the fault to the ABS module, then flash the brake indicator ON and OFF. The IPC will continue to flash the brake indicator until the ABS indicator circuit fault is resolved, or until the ignition switch is turned to the OFF position, whichever occurs first.

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