The anti-lock electronic control module (2C018) located in the center of the instrument panel.
RABS valve (dual solenoid electro-hydraulic valve) is located under the brake master cylinder (2140).
The rear brake anti-lock sensor (2B190) and rear brake anti-lock sensor ring are located in the rear differential case (4204).
The yellow ABS warning indicator is located in the instrument cluster.
The RABS diagnostic connector is located in the cab behind the right side cowl side trim panel (02345).
Diode/resistor element located in the wire harness at the windshield washer solvent reservoir.
RABS sensor test connector with cap located in the engine compartment on the bulk head above the brake master cylinder.
The anti-lock electronic control module performs system tests during start-up and normal operation. The RABS valve, rear brake anti-lock sensor, and fluid level circuits are monitored for proper operation. If a concern is found, the anti-lock electronic control module deactivates and the yellow ABS warning indicator illuminates.
Most concerns cause the warning indicator to stay illuminated until the ignition is turned off, at which time the anti-lock electronic control module retains the diagnostic trouble code (DTC) in memory (also referred to as keep alive memory or KAM). At any time while the ignition is turned on, a DTC may be obtained. A special DTC 16 indicates that the system is operating normally. However, those concerns associated with loss of power to the anti-lock electronic control module cause the system to be deactivated and the yellow ABS warning indicator to be illuminated, but do not cause a DTC.
The system diode is actually a diode/resistor element. The diode/resistor element prevents a false DTC 12 from being set when the parking brake is applied.
The brake on/off (BOO) switch, when activated, signals the anti-lock electronic control module that a braking condition is occurring.
The rear anti-lock brake system (RABS) continuously monitors rear wheel speed with a rear brake anti-lock sensor mounted in the rear differential case. When the teeth on the rear brake anti-lock sensor ring, mounted on the ring gear, pass the RABS sensor pole piece, an AC voltage is induced in the sensor circuit with a frequency proportional to the average rear wheel speed. In the event of an impending lockup during braking, at vehicle speeds above approximately 8 kph (5 mph), the anti-lock electronic control module senses the drop in rear wheel speed. If the rate of deceleration is excessive, the anti-lock electronic control module activates the RABS valve, causing the isolation valve to close. With the isolation valve closed, the rear wheel cylinders (2261) are isolated from the brake master cylinder and the rear brake fluid pressure cannot increase. If the rate of deceleration is still excessive, the anti-lock electronic control module will energize the dump solenoid with a series of rapid pulses to bleed the rear wheel cylinder fluid into an accumulator built into the RABS valve. This reduces the rear wheel cylinder brake fluid pressure and allows the wheels (1007) to spin at vehicle speed. The anti-lock electronic control module pulses the dump and isolation solenoids in a manner that will keep the wheels rotating while still maintaining high levels of deceleration during braking.
Once stopped, the operator releases the brake pedal (2455), the isolation valve de-energizes and any fluid in the accumulator returns to the brake master cylinder. Normal brake operation resumes.