Fig. 7 Location Controller Anti-Lock Brake (CAB)

The primary functions of the (CAB) are:

²(1) Detect wheel locking tendencies.

²(2) Control fluid modulation to the brakes while in Anti-Lock mode.

²(3) Monitor the system for proper operation.

²(4) Provide communication to the DRB II while in diagnostic mode.

The (CAB) continuously monitors the speed of each wheel, through the signals generated at the Wheel Speed Sensors, to determine if any wheel is beginning to lock. When a wheel locking tendency is detected, the (CAB) will isolate the master cylinder from the wheel brakes. This is done by activating the Isolation Valves. The (CAB) then commands the appropriate Build or Decay valves to modulate brake fluid pressure in some or all of the hydraulic circuits. The fluid used for modulation comes from the booster servo circuit. The (CAB) continues to control pressure in individual hydraulic circuits until a locking tendency is no longer present.

The (ABS) system is constantly monitored by the (CAB) for proper operation. If the (CAB) detects a fault, it can disable the Anti-Lock braking function. Depending on the fault, the (CAB) will light one or both of the brake warning lamps.

The (CAB) contains a System Diagnostic Program which triggers the brake system warning lamps when a system fault is detected. Faults are stored in a diagnostic program memory. There are 19 fault codes that may be stored in the (CAB) and displayed through the DRB II. These fault codes will remain in the (CAB) memory even after the ignition has been turned off. These fault codes will remain in memory

until they are cleared with the DRB II, or automatically erased from the memory after (50) ignition switch on/off cycles.

CONTROLLER ANTI-LOCK BRAKE (INPUTS)

²Four wheel speed sensors.

²Boost pressure transducer.

²Primary pressure transducer.

²Low fluid level switch.

²Differential pressure switch.

²Parking brake switch.

²Dual function pressure switch (warning pressure only)

²Stop lamp switch.

²Ignition switch.

²System relay voltage.

²Ground.

²Low Accumulator

CONTROLLER ANTI-LOCK BRAKE (OUTPUTS)

²Ten modulator valves-3 decay, 3 build and 4 isolation.

²Red Brake warning lamp.

²Amber Anti-Lock Warning Lamp.

²System relay actuation.

²Diagnostic communication.

ABS SYSTEM DIAGNOSTIC CONNECTOR

The Bendix Anti-Lock system diagnostic connector is located under the lower dash panel or in the area of the fuse box (Fig. 8). The fuse box is located behind the access panel that is on the bottom portion of the dash panel, left of the steering column. The diagnostics connector is a blue 6 way connector.

Fig. 8 A.B.S. Diagnostic Connector Location

Ä

ANTI-LOCK SYSTEM RELAYS AND WARNING LAMPS

PUMP/MOTOR RELAY

Pump/Motor power is supplied by the Pump/Motor Relay. The Pump/Motor relay is located inside the Power Distribution Center (PDC). Thee relay coil is energized by a ground from the Dual Function Pressure Switch. See (Fig. 9) for the location of the pump/motor relay in the (PDC).

SYSTEM RELAY

The (ABS) Modulator Valves and Anti-Lock Warning Lamp Relay are controlled through a System Relay. The System relay is located on the top left inner fender behind the headlight (Fig. 10). The system relay provides power to the (CAB) for modulator valve operation (pins 47 and 50) after the start-up cycle when the ignition is turned on.

ANTI-LOCK WARNING LAMP RELAY

The Anti-Lock Warning Lamp is controlled by the Yellow Light Relay. See (Fig. 10) for location behind the left headlight. With the relay de-energized, the lamp is lit. When the system relay is energized by the (CAB), the Anti-Lock Warning Lamp relay is energized, and the lamp is turned off. Thus, the lamp will be lit if the (CAB) is disconnected or if a system fault causes (ABS) function to be turned off, or if the system relay fails open.

ANTI-LOCK WARNING LAMP OFF

System Relay (normally open) and Yellow Light Relay (normally closed) Energized.

When the (CAB) energizes the system relay by providing 12 volts to pin 57. The voltage flow in the coil closes the system relay. Electrical current is then provided to pins 47 and 50 of the (CAB) to provide power to the modulator valves. This voltage also energizes the Anti-Lock Warning Lamp Relay Switch. This breaks the ground path to the Anti-Lock Warning Lamp and the lamp is turned off.

The (CAB) by itself, also can turn on the Anti-Lock Warning Lamp. The (CAB) can turn on the Anti-Lock Warning Lamp by providing a ground at pin 15.

ANTI-LOCK WARNING LAMP ON

System Relay and Anti-Lock Warning Lamp Relay De-Energized.

When the Amber Anti-Lock Warning Lamp is on, there is no current flow from the (CAB) at pin 57. The system relay coil is NOT energized. No electrical current flows to pins 47 and 50 (modulator valve power),

ANTI-LOCK 10 BRAKE SYSTEM 5 - 83

Fig. 9 Pump/Motor

Fig. 10 ABS System Relay And Yellow Lamp Relay

Location

or to the Anti-Lock Warning Lamp relay coil. Thus, the Anti-Lock Warning Lamp Relay is not energized. The Anti-Lock Warning Lamp is grounded through the Anti-Lock Warning Lamp relay contacts. The Anti-Lock Warning Lamp is illuminated.