Circuit Operation
The brake warning indicator on the instrument cluster illuminates under the following conditions:
| • | The ignition is in the start position. |
| • | The park brake is set. |
| • | The brake pressure differential switch has a difference in pressure (310 ABS only). |
| • | The master cylinder brake fluid level is low (325 ABS only). |
| • | The electronic brake control module (EBCM) senses an ABS problem. |
These conditions are explained in detail below.
Ignition
When the vehicle is started the instrument cluster runs a bulb check on the indicator lights for three seconds. The lights then turn off. For more information refer to Indicator Description in Instrument Panel, Gauges and Console.
Park Brake
The park brake switch closes when the park brake is set. Ground is applied to the body control module (BCM) CKT 1134 (LT BLU). When the BCM senses the ground, the BCM will send a class 2 signal to the instrument cluster which will illuminate the brake warning indicator.
Brake Pressure Differential Switch (310 ABS only)
The brake pressure differential switch closes when the switch senses a difference in brake line pressure. Ground is applied to the electronic brake control module (EBCM) through CKT 680 (PPL). When the EBCM senses the ground, the EBCM will send a class 2 signal to the instrument cluster which will illuminate the brake warning indicator.
Brake Fluid Level (325 ABS only)
When the brake fluid level in the master cylinder is low, the brake fluid level indicator sensor closes. Ground is applied to the electronic brake control module (EBCM) through circuit 333 (PPL). When the EBCM senses the ground, the EBCM will send a class 2 signal to the instrument cluster which will illuminate the brake warning indicator.
EBCM
The warning 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 signal through the Class 2 serial data line to illuminate the brake warning indicator. The indicator warns the driver that a problem exists in the ABS system. When this happens the antilock brake light will also illuminate. Refer to Antilock Brake System for further information.
