Brake Warning Indicator: Description and Operation
BRAKE/PARK BRAKE INDICATORA brake indicator is standard equipment on all instrument clusters. The brake indicator is located near the lower edge of the instrument cluster overlay, to the left of center. The brake indicator consists of a stencil-like cutout of the word "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 lens behind the cutout in the opaque layer of the overlay causes the "BRAKE" text to appear in red through the translucent outer layer of the overlay when the indicator is illuminated from behind by a Light Emitting Diode (LED) 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. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming, and electronic messages received by the cluster from the Controller Antilock Brake (CAB) over the Chrysler Collision Detection (CCD) data bus. The brake indicator Light Emitting Diode (LED) receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or Start positions; 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 indicator remains illuminated until the cluster receives lamp-OFF messages from the CAB, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Park Brake Switch Status - Each time the cluster receives a hard wired input from the park brake switch indicating that the park brake is applied or not fully released, the brake indicator will be illuminated. The indicator remains illuminated until the park brake switch input indicates that the park brake is released, or until the ignition switch is turned to the OFF position, whichever occurs first.
- 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 park brake switch on the park brake pedal mechanism provides a hard wired ground input to the instrument cluster circuitry through the park brake switch sense circuit whenever the park brake is applied or not fully released. The brake warning indicator switch on the brake combination valve provides a hard wired ground input to the CAB circuitry through the brake warning indicator driver circuit whenever the pressures in the two halves of the split brake hydraulic system are unequal. 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. The park brake switch input to the instrument cluster and the brake pressure switch input to the CAB can be diagnosed using conventional diagnostic tools and methods. For proper diagnosis of the antilock brake system, the CAB, the CCD data bus, or the message inputs to the instrument cluster that control the brake indicator, a DRB III scan tool is required. Refer to the appropriate diagnostic information.