Brake Warning Indicator: Description and Operation

OPERATION
The red Brake warning lamp is located in the instrument cluster and is used to indicate a low brake fluid condition or that the parking brake is applied. In addition, the brake warning lamp is turned on as a bulb check by the ignition switch when the ignition switch is placed in the crank position. Problems with this system will generally be of the type where the warning lamp fails to turn on when it should, or remains on when it should not.

The warning lamp bulb is supplied a 12 volt ignition feed anytime the ignition switch is on. The bulb is then illuminated by completing the ground circuit either through the park brake switch, the fluid level sensor in the master cylinder reservoir, or the ignition switch in the crank position. As the fluid drops below the minimum level, the fluid level sensor closes the brake warning light circuit. The Controller Antilock Brakes CAB will also activate the brake warning lamp if there is a fault in the ABS system, and the amber ABS lamp fails to operate. Both the red and the amber lamps will flash when the system is placed in the diagnostic mode with the DRB scan tool. ABS operation is disabled while in the diagnostics mode.

With the ignition in the Crank position, the Red Brake Warning Lamp will turn on as a bulb check. The Amber ABS Warning Lamp and the Traction Control Lamps will stay on for 1-2 seconds then turn off, ounce verification of the self diagnosis is completed.

CIRCUIT OPERATION
ABS Warning Lamp
The ABS warning lamp is an output from the Controller Anti-Lock Brake (CAB) module. It is used to alert the operator of a problem in the ABS system. The G19 circuit from the CAB is used to detect a problem. If a problem is detected, the module grounds circuit G19 and the lamp in the message center is illuminated.

The lamp can also be illuminated if the ABS main relay switches from its normal ON position to its OFF, grounded position.

Power for the lamp in the message center is provided by circuit G5. This circuit is protected by a 5 amp fuse located in cavity 14 if the junction block. Power for the fuse is supplied on circuit A21. This circuit is HOT in the RUN position only

Power for the A21 circuit is supplied from the Power Distribution Center (PDC) on circuit A1. The A1 circuit is protected by a 20 amp fuse located in cavity A of the PDC.

Brake Warning Lamp
The brake warning lamp is used to alert the operator of a problem in the vehicles braking system. This lamp also illuminates when the ignition switch is turned to the START position to perform a self check.

Power for the lamp is supplied on circuit F11. This circuit is HOT when the ignition switch is in the OFF (unlock), START, and RUN positions. The F11 circuit is protected by a 5 amp fuse located in cavity 17 of the junction block.

There are two switches used in this system and they are wired in parallel form. A parking brake switch, located on the parking brake mechanism, will illuminate the lamp if the normally OPEN switch is CLOSED. This switch is case grounded.

The second switch used is the brake warning lamp switch. This switch in normally OPEN. When the brake system pressure is below the predetermined level the switch CLOSES and completes a path to ground.

The G9 circuit is used to connect the switches to the cluster. Grounding for the brake warning lamp switch is completed on the Z1 circuit which terminates at the left front frame rail.

If the vehicle is built for sale in Canada the parking brake switch is used for the Daytime Running Lamp (DRL) system.

On vehicles equipped with anti-lock brakes the operation of the warning lamp is controlled by the ABS control module.