Parking Brake Warning Lamp: Description and Operation

BRAKE/PARK BRAKE INDICATOR
A brake indicator is standard equipment on all instrument clusters. The brake indicator is located in the Information Center area of the instrument cluster, to the right of center. The brake indicator consists of stencil-like cutouts of the word "BRAKE" and the International Control and Display Symbol icons for "Brake Failure" and "Parking Brake" 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. A red Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the "BRAKE" text and the two icons to appear in red 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.

The brake indicator gives an indication to the vehicle operator when the parking brake is applied, or when there are certain brake hydraulic system malfunctions. 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 instrument cluster electronic circuit board based upon cluster programming, and electronic messages received by the cluster from the Controller Antilock Brake (CAB) and the Central Timer Module (CTM) over the Programmable Communications Interface (PCI) data bus. 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 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 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 four seconds as a bulb test.

- Brake Lamp-On Message - Each time the cluster receives a lamp-on message from the CAB, the brake indicator will be illuminated. The CAB can also send brake lamp-on messages as feedback during ABS diagnostic procedures. 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.

- Park Brake Applied Message (Manual Transmission) - Each time the cluster receives a park brake applied message while the ignition switch is in the On position, the brake indicator will be illuminated. If the engine is not running when the park brake applied message is received, the brake indicator illuminates solid. If the engine is running when the park brake applied message is received, the brake indicator flashes on and off. The indicator remains illuminated solid or flashing until the park brake is released, or until the ignition switch is turned to the Off position, whichever occurs first.

- Park Brake Applied Message (Automatic Transmission) - Each time the cluster receives a park brake applied message while the ignition switch is in the On position, the brake indicator will be illuminated. If the transmission is in Park or Neutral when the park brake applied message is received, the brake indicator illuminates solid. If the transmission is in any position except Park or Neutral when the park brake applied message is received, the brake indicator flashes on and off. The indicator remains illuminated solid or flashing until the park brake is released, or until the ignition switch is turned to the Off position, whichever occurs first.

- Communication Error - If the cluster receives no lamp-on or lamp-off messages from the CAB for three consecutive seconds, the brake indicator will be illuminated. The indicator remains illuminated until the cluster receives a single lamp-off message from the CAB.

- Actuator Test - Each time the instrument cluster is put through the actuator test, the brake indicator will be turned on, then off again during the bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry.

The CTM continually monitors the status of the park brake switch on the park brake pedal mechanism. The CTM then sends the proper park brake status messages to the instrument cluster. 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 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 brake hydraulic system malfunction and/or that the ABS system has become inoperative. The CAB will store a Diagnostic Trouble Code (DTC) for any malfunction it detects.

For further diagnosis of the brake indicator or the instrument cluster circuitry that controls the LED, (Refer to ELECTRICAL/INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING). For proper diagnosis of the park brake switch, the brake fluid level switch, the ABS, the CTM, the CAB, the PCI data bus, or the electronic message inputs to the instrument cluster that control the brake indicator, a DRBIII(R) scan tool is required. Refer to the appropriate diagnostic information.