RAM 2500 Truck 4WD V8-5.9L VIN Z LDC (1998)
Brake Warning Indicator: Description and Operation
General Information
SYSTEM OPERATION
The brake warning lamp gives an indication when the parking brake is applied, when the pressures in the two halves of the split brake hydraulic
system are unequal, if the Anti-lock Brake System (ABS) lamp has failed and an ABS fault occurs, and during ABS diagnostics. The lamp is
turned on by the instrument cluster circuitry for about two seconds when the ignition switch is moved to the Start position as a bulb test. After the
bulb test, the lamp is controlled by a hard-wired input from the parking brake switch and/or by the instrument cluster circuitry based upon
messages received from the Controller Anti-lock Brake (CAB) on the Chrysler Collision Detection (CCD) data bus.
The CAB turns the lamp on or off based upon the results of the ABS self-tests. The CAB continually monitors the ABS circuits and sensors,
including the brake warning switch and the ABS lamp, to decide whether the system is in good operating condition. The CAB then sends the
proper messages to the instrument cluster on the CCD data bus to turn the lamp on or off. If the CAB turns the lamp on after the bulb test, it
indicates that the CAB has detected a system malfunction.
The parking brake switch is hard-wired to the instrument cluster and closes to ground when the parking brake is applied. The brake warning switch
is hard-wired to the CAB and 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.
After the bulb test, if the red brake warning lamp remains illuminated with the parking brake released, the base brake system may not be
operational. The vehicle should never be operated while the red brake warning lamp is illuminated.
