As an add-on logic to the antilock brake system (ABS) base algorithm, electronic brake force distribution (EBD) works in a range in which the intervention thresholds for ABS control are not reached yet.

EBD ensures that the rear wheels are sensitively monitored for slip with respect to the front axle. If slip is detected, the inlet valves for the rear wheels are switched to pressure hold to prevent a further increase in pressure at the rear-wheel brakes, thus electronically reproducing a pressure-reduction function at the rear-wheel brakes.

Replacement Tires

Tire size is important for proper performance of the antilock brake system (ABS). Replacement tires should be the same size, load range, and construction as the original tires. Replace tires in axle sets and only with tires of the same tire performance criteria (TPC) specification number. Use of any other size or type may seriously affect the ABS operation.

Important: There is no serviceable or removable electrically erasable programmable read only memory (EEPROM). The electronic brake control module (EBCM) must be replaced as an assembly.

The EBCM is attached to the hydraulic unit in the engine compartment. The controlling element of ABS 5.3 is a microprocessor-based EBCM. Inputs to the system include the 4 wheel speed sensors, the stop lamp switch, the ignition switch, and battery voltage. There is an output to a bi-directional serial data link, located in the data link connector (DLC) for service diagnostic tools and assembly plant testing.

The EBCM monitors the speed of each wheel. If any wheel begins to approach lockup and the brake switch is closed, brake pedal depressed, the EBCM controls the solenoids to reduce brake pressure to the wheel approaching lockup. Once the wheel regains traction, brake pressure is increased until the wheel again begins to approach lockup. This cycle repeats until either the vehicle comes to a stop, the brake pedal is released, or no wheels approach lockup.

Additionally, the EBCM monitors itself, each input, except the serial data link, and each output for proper operation. If it detects any system malfunction, the EBCM will store a DTC in nonvolatile memory (EEPROM). Diagnostic trouble codes (DTCs) will not disappear if the battery is disconnected.

The front wheel speed sensors are of a variable reluctance type. Each sensor is attached to the steering knuckle, close to a toothed ring. The result, as teeth pass by the sensor, is an alternating current (AC) voltage with a frequency proportional to the speed of the wheel. The magnitude of the voltage and frequency increase with increasing speed. The sensor is not repairable, nor is the air gap adjustable.

The toothed ring mentioned above is pressed onto the wheel-side, outer, constant velocity joint. Each ring contains 40 equally spaced teeth. Exercise care during service procedures to avoid prying or contacting this ring. Excessive contact may cause damage to one or more teeth.

The rear wheel speed sensors operate in the same manner as the front wheel speed sensors. Each sensor is attached to the backing plate, close to a toothed ring. They incorporate a length of flexible harness with the connector attached to the end of the harness. The rear wheel speed rings are incorporated into the hub drum.

The valve relay and the motor pump relay are located inside the electronic brake control module (EBCM) and are not replaceable. If one should fail, replace the EBCM.

The wiring harness is the mechanism by which the electronic brake control module (EBCM) is electrically connected to power and to ground, to the wheel speed sensors, the fuses, the switches, the indicators, and the serial communications port. The components, considered part of the wiring harness, are the wires that provide electrical interconnection, and connectors, terminals, pins, contacts, or lugs, that provide an electrical/mechanical interface from the wire to a system component.

The electronic brake control module (EBCM) continuously monitors itself and the other antilock brake system (ABS) components. If the EBCM detects a problem with the system, the amber ABS indicator will light continuously to alert the driver to the problem. An illuminated ABS indicator indicates that the ABS system has detected a problem that affects the operation of ABS. No antilock braking will be available. Normal, non-antilock brake performance will remain. In order to regain ABS braking ability, the ABS must be serviced.

Important: The electronic brake force distribution (EBD) indicator lamp wiring is connected to the parking brake indicator. If the parking brake indicator is turned ON when you are driving, check on whether the parking brake lever is engaged or the brake fluid level is low. If the system has no problem, the EBD system is working improperly. The EBD system must be serviced.

The red BRAKE indicator will be illuminated when the system detects a low brake fluid level in the master cylinder or when the parking brake switch is closed, the parking brake is engaged, or the EBD system is disabled.