Circuit Operation
The brake warning indicator on the instrument cluster illuminates under the following conditions:
| • | The instrument cluster bulb test is occurring. |
| • | The park brake is set. |
| • | The master cylinder brake fluid level is low. |
| • | The electronic brake control module sends a Class 2 message to the instrument cluster. |
These conditions are explained in detail below. In all cases positive voltage is applied to the brake warning indicator through circuit 39.
Instrument Cluster Bulb Test
When the ignition switch is turned to the RUN position, the instrument cluster performs an internal bulb test on the brake warning indicator. The indicator illuminates for approximately 3 seconds and then turns off.
Park Brake
The park brake switch closes when the park brake is set. On Domestic and Gulf States vehicles, ground is applied through circuit 1134, the DRL module and circuit 33 to the instrument cluster. The brake indicator illuminates. On Europe and Japan vehicles, ground is applied through circuit 33 to the cluster.
Brake Fluid Level
When the brake fluid level in the master cylinder is low, the brake fluid level indicator sensor closes. Ground is applied through the sensor and circuit 33 to the instrument cluster. The brake indicator illuminates.
EBCM Class 2
The brake indicator is also controlled by the ABS system through the class 2 serial data line. The electronic brake control module (EBCM) sends a class 2 message to illuminate the brake indicator. The indicator warns the customer that a problem exists in the ABS system. Refer to ABS brakes for further information.
