Grand Cherokee 2WD L6-4.0L VIN S (1997)
Brake Warning Indicator: Description and Operation
Brake Warning Lamp Circuit Operation
SYSTEM OPERATION
A red warning lamp is used for the service brake portion of the hydraulic system. The lamp is located in the instrument cluster. The red warning light
alerts the driver if a pressure differential exists between the front and rear hydraulic systems. The light also alerts the driver when the parking brakes are
applied.
The brake warning lamp gives an indication when the parking brake is applied, or when the pressures in the two halves of the split brake hydraulic
system are unequal. The lamp is turned on by the instrument cluster circuitry for about four seconds when the ignition switch is turned to the On
position as a bulb test. After the bulb test, the lamp is controlled by the instrument cluster circuitry based upon a message received from the Body
Control Module (BCM) on the Chrysler Collision Detection (CCD) data bus.
The BCM uses inputs from the parking brake switch and the brake warning switch to decide whether the brake warning lamp should be on or off.
The BCM then sends the proper message to the instrument cluster on the CCD data bus to turn the lamp on or off.
The brake warning switch closes to ground when it senses unequal hydraulic pressures in the two halves of the split brake hydraulic system,
possibly due to low brake fluid level or brake fluid leakage. The parking brake switch closes to ground when the parking brake is applied.
