Parking Brake Warning Lamp: Description and Operation
BRAKE/PARK BRAKE INDICATORA brake indicator is standard equipment on all instrument clusters The brake indicator is located near the left edge of the instrument cluster, to the left of the tachometer. There are two versions of the brake indicator. The version used depends upon the market for which the vehicle is manufactured. The version used for vehicles manufactured for the United States market consists of the word "BRAKE" imprinted on a red lens. The version for all other markets [Rest-of-World (ROW)] has two International Control and Display Symbol icons imprinted on the red lens; one is the icon for "Brake Failure", and the other is the icon for "Parking Brake". In either case, the lens is located behind a cutout 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. The "BRAKE" text or the two icons appear silhouetted against a red field through the translucent outer layer of the overlay when the indicator is illuminated from behind by a Light Emitting Diode (LED), which is soldered onto the instrument cluster electronic circuit board. The brake indicator lens is serviced as a unit with the instrument cluster lens, hood and mask unit.
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 certain faults are detected in the Antilock Brake System (ABS). 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 Anti-lock Brake (CAB) over the Programmable Communications Interface (PCI) data bus, and a hard wired input to the cluster from the park brake 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 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 three 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 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 Switch Input - Each time the cluster 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, the brake indicator is illuminated. The indicator remains illuminated until the park brake switch sense input to the cluster 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.
- Communication Error - If the cluster receives no lamp-on or lamp-off messages from the CAB for six consecutive seconds, the brake indicator is illuminated. The indicator remains illuminated until the cluster receives a single valid 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 for the duration of the test to confirm the functionality of the LED and the cluster control circuitry.
The park brake switch on the park brake lever mechanism provides a hard wired ground input to the instrument cluster circuitry through the red brake warning indicator driver 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 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 indicator, refer to Instrument Cluster Diagnosis and Testing. The park brake switch input to the instrument cluster may be diagnosed using conventional diagnostic tools and methods. For proper diagnosis of the brake fluid level switch input to the CAB, the ABS, the CAB, the PCI data bus, or the electronic message inputs to the instrument cluster that control the brake indicator, a DRBIII scan tool is required. Refer to the appropriate diagnostic information.