RAM 2500 Truck 2WD L6-359 5.9L DSL Turbo VIN D FI (1997)
Brake Warning Indicator: Description and Operation
SYSTEM OPERATION
Anti-Lock Brake System Lamp
The Anti-Lock Brake System (ABS) lamp gives the driver an indication when the standard Rear Wheel Anti-Lock (RWAL) or optional all-wheel
ABS system is faulty or inoperative. See the following description that applies to the brake system used on the vehicle being serviced.
Rear Wheel Anti-Lock
On vehicles equipped with the standard RWAL brake system, the ABS lamp is switched to ground by the RWAL control module. The RWAL
control module lights the lamp when the ignition switch is turned to the Start position as a bulb test. The lamp will stay on for about four
seconds after vehicle start-up to indicate that a system self-test is in progress.
If the ABS lamp remains on after start-up, or comes on and stays on while driving, it may indicate that the RWAL control module has detected
a system malfunction and/or that the RWAL system has become inoperative.
Anti-Lock Brake System
The optional all-wheel ABS lamp is grounded through the normally closed contacts of the de-energized ABS lamp relay When the ignition
switch is turned to the Start position, the lamp is lighted as a bulb test. The lamp will stay on for about four seconds after vehicle start-up to
indicate a system self-test is in progress. If the self-test is successfully completed, the ABS lamp relay is energized by the Controller Anti-lock
Brake (CAB) module, which turns the lamp off.
The CAB module energizes the ABS lamp relay to turn the ABS lamp off, and de-energizes the ABS lamp relay to turn the ABS lamp on. If
the ABS lamp remains on after start-up, or comes on and stays on while driving, it may indicate that the CAB module has detected a system
malfunction and/or that the ABS system has become inoperative.
Brake Warning Lamp
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, or when certain problems are detected in the Rear Wheel Anti-Lock (RWAL) or Anti-Lock Brake Systems (ABS). The lamp
is turned on when the ignition switch is turned to the Start position as a bulb test. After the bulb test, the lamp is controlled by hard-wired inputs
from the parking brake switch, the brake warning switch, or the RWAL control module/Controller Anti-lock Brake (CAB).
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. The
RWAL control module or CAB can also turn on the brake warning lamp if certain brake system faults are detected.
CIRCUIT OPERATION
Rear Wheel ABS Warning Lamp
The Controller, Antilock Brake (CAB) provides ground for the instrument cluster Check Antilock warning lamp on circuit G19. Circuit F14
provides voltage to the instrument cluster to feed the warning lamp.
All Wheel ABS Warning Lamp
The Controller, Antilock Brakes (CAB) provides ground for the ABS warning lamp in the message center through the normally closed contacts in
the ABS warning lamp relay. When the ignition switch is in the START position, the lamp illuminates as a bulb test for approximately 3 to 5
seconds while the CAB performs a system self-test. While closed, the relay contacts complete the ground path for the ABS warning lamp by
connecting circuit G19 from the lamp to ground on circuit Z1. Power for the lamp is supplied by circuit F14.
If the system self-test is successfully completed, the CAB energizes the ABS warning lamp relay by providing ground for the relay coil on circuit
B47. When the relay energizes, its contacts open and disconnect circuits G19 and Z1. Circuit A20 from fuse 14 in the fuse block supplies power to
the coil side of the relay.
Circuit G19 from the ABS warning splices to the ABS warning lamp and the CAB.
