The ABS VI Antilock Braking System consists of the following components:

The conventional brake system includes the following components:

The ABS VI includes the following components:

The ABS Brake Modulator/Motor Pack Assembly controls hydraulic pressure to the following areas:

The ABS Brake Modulator/Motor Pack Assembly controls hydraulic pressure by modulating the hydraulic pressure. This action prevents wheel slip.

The basic ABS brake modulator configuration consists of the following components:

The ABS brake motor pack consists of the following components:

The hydraulic modulator is located in the left hand side of the engine compartment, in front of the master cylinder.

Refer to Base Brake System and Antilock Brake System in this section for more information.

The Electronic Brake Control Module (EBCM) controls the ABS VI. A microprocessor controls the EBCM.

The inputs to the system include the following components:

The outputs include the following components:

A serial data line is provided for service diagnostic tools and assembly plant testing.

The EBCM monitors the speed of each wheel.

The EBCM controls the motors and the solenoids in order to reduce brake pressure to a particular wheel when the following conditions exist:

This cycle will repeat until one of the following conditions exists:

If any system malfunction is detected, the EBCM will store a DTC in nonvolatile memory (DTCs will not disappear if the battery is disconnected).

The EBCM is located inside the left hand side of the Instrument Panel, above the accelerator pedal.

Refer to Self-Diagnostics for more information.

The front wheel speed sensors are of a variable reluctance type. Each sensor is attached to the knuckle assembly in close proximity to a toothed ring. An AC voltage is generated when the toothed ring passes by the sensor. The magnitude and frequency are proportional to the speed of the wheel and both will increase with increasing speed. The sensor is not repairable, nor is the air gap adjustable.

The sensor is not repairable.

The air gap is not adjustable.

A single rear wheel speed sensor is used for this ABS application and is located on the rear differential. It operates in the same manner as the front wheel speed sensors. However, the toothed ring is located within the rear differential.

The sensor and the toothed ring are not repairable.

The air gap cannot be adjusted.

The Electronic Brake Control Relay is a normally-open contact type.

The Electronic Brake Control Relay has special contact material to handle the high currents required for the ABS VI operation.

The relay allows battery voltage and current to be supplied to the EBCM. The EBCM supplies power to the motors and the solenoids.

The relay is located on the LH side of the engine compartment, mounted on the inner fender next to the hydraulic modulator.

The proportioning valve contains a normally-open shuttle switch. This switch monitors front brake hydraulic pressure. This switch closes when there is a loss of pressure in the front brakes.

When the shuttle switch closes, it causes the red BRAKE warning lamp to turn ON. It also alerts the EBCM of the base brake failure. The EBCM then disable the ABS system. The shuttle switch is mounted on top of the proportioning valve.

Refer to Fluid Level Switch in Hydraulic Brakes.

The EBCM uses an accelerometer to sense vehicle motion.

The EBCM provides power (5 volts) and ground to the accelerometer. The accelerometer sends a voltage signal back to the EBCM relative to vehicle motion. This signal is about 2.4 to 2.6 volts at zero speed change (constant motion), the voltage signal decreases when the vehicle is under acceleration, and the voltage signal increases when the vehicle is under deceleration.

The accelerometer is located inside the parking brake lever bezel.

The four-wheel drive switch is used to notify the EBCM when the vehicle is in four-wheel drive mode. Under certain road conditions, a vehicle in four-wheel drive mode requires special measures to support the reference vehicle speed by means of an accelerometer.

The four-wheel drive switch is mounted on the transfer case.

The EBCM uses the Powertrain Control Module (PCM) to increase engine idle speed.

When the transfer case is set in 4H or 4L, the EBCM may command the Powertrain Control Module (PCM) to increase the idle speed during an ABS event.

The reason to increase engine speed above base idle is to reduce engine-induced braking. Engine braking, especially on icy road conditions, tends to reduce ABS performance.

The EBCM logic determines when it is necessary to idle-up. However, the PCM will ignore any requests to idle-up from the EBCM until the vehicle speed has reached at least 20 km/h (12 mph). The reason for this default in vehicle speed is to avoid a fast idle at all times when the idle-up circuit has been shorted to ground due to an electrical problem.

The wiring harness is the mechanism which electrically connects the EBCM to the following components:

And on vehicles equipped with 4WD, the EBCM is also connected to the accelerometer, 4WD switch and PCM.

The wiring harness consists of the following components:

A jumper harness located between each wheel speed sensor and the main wiring harness.

Each jumper harness is made of highly flexible twisted pair wiring.

The wiring exists because the main harness must connect to the suspension of the vehicle. Therefore, the wiring in this area is subjected to the same motion as a spring or a shock absorber. Any repair to this section of wiring will result in stiffening. Stiffening will eventually result in failure due to wire fatigue.

The wheel speed sensor jumper harnesses are not repairable and must be replaced. Do not attempt to solder, splice, or crimp the harnesses. Eventual failure will occur.

Refer to Wheel Speed Sensor Jumper Harness Replacement .

The Electronic Brake Control Module (EBCM) continuously monitors itself and other ABS components.

If the EBCM detects a problem with the system, the amber ABS warning indicator will light continuously (solid indicator) in order to alert the driver of the problem.

Normal (non-antilock) braking will remain. In order to regain ABS braking ability, the ABS must be serviced.

The amber ABS warning indicator flashes to warn the driver of an existing malfunction with the base brake system and the EBCM cannot illuminate the red BRAKE warning indicator. In this situation, the vehicle must be serviced immediately in order to regain full base and ABS operation.

Since the brake pedal feedback normally associated with ABS operation does not occur with ABS VI, there is an additional indicator in the instrument cluster to inform the driver of ABS operation. The blue ABS ACTIVE indicator will illuminate during an ABS event and during system initialization.

The following indicators will illuminate any time when the EBCM suspects that the ABS operation is degraded because of a system malfunction:

The amber ABS warning indicator

The red BRAKE warning indicator illuminates when the following conditions exist:

The red BRAKE warning indicator alerts the driver that a base brake problem may exist.

Refer to Brake Warning Cell 41 in Electrical Diagnosis for further diagnosis of the red BRAKE warning indicator.

The power distribution system of the vehicle consists of the fuses and the ignition switch.

The following fuses are:

Fuse box 1 is located on the RH side of the engine compartment, in front of the battery.

Fuse block 2 is located under the LH side of the I/P.

Refer to Power Distribution, Cell 10, and Fuse Block Details, Cell 11, in Electrical Diagnosis for fuse locations and additional information.