ABS Service Information: Overview Dodge Durango II

DESCRIPTION

The antilock brake system (ABS) is an electronically operated, three channel brake control system. The vehicle has Electronic Brakeforce Distribution (EBD) designed into the system which eliminates the combination/proportioning valve.

The system is designed to prevent wheel lockup and maintain steering control during braking. Preventing lockup is accomplished by modulating fluid pressure to the wheel brake units.

The hydraulic system is a four channel design with traction control. The front wheel brakes are controlled individually and the rear wheel brakes in individually. The ABS electrical system is separate from other electrical circuits in the vehicle. A specially programmed controller antilock brake unit operates the system components.

ABS system major components include

1. Antilock Brake Module (ABM)
2. Hydraulic Control Unit (HCU)
3. Wheel Speed Sensors (WSS)
4. G-Sensor
5. ABS Warning Light

OPERATION

When wheel slip is detected during a brake application, the ABS enters antilock mode. During antilock braking, hydraulic pressure in the individual wheel circuits is controlled to prevent any wheel from slipping. A separate hydraulic line and specific solenoid valves are provided for each wheel. The ABS can decrease, hold, or increase hydraulic pressure to each wheel brake. The ABS cannot, however, increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking

During antilock braking, a series of rapid pulsations is felt in the brake pedal. These pulsations are caused by the rapid changes in position of the individual solenoid valves as the ICU responds to wheel speed sensor inputs and attempts to prevent wheel slip. These pedal pulsations are present only during antilock braking and stop when normal braking is resumed or when the vehicle comes to a stop. A ticking or popping noise may also be heard as the solenoid valves cycle rapidly. During antilock braking on dry pavement, intermittent chirping noises may be heard as the tires approach slipping. These noises and pedal pulsations are considered normal during antilock operation.

Vehicles equipped with ABS may be stopped by applying normal force to the brake pedal. Brake pedal operation during normal braking is no different than that of previous non-ABS systems. Maintaining a constant force on the brake pedal provides the shortest stopping distance while maintaining vehicle stability.

The Wheel Speed Sensor consists of a magnet (1) surrounded by windings from a single strand of wire (5). The sensor sends a small AC signal to the ABM. This signal is generated by magnetic induction. The magnetic induction is created when a toothed sensor ring (exciter ring or tone wheel) (4) passes the stationary magnetic WSS.

When the ring gear is rotated, the exciter ring (4) passes the tip of the WSS. As the exciter ring tooth approaches the tip of the WSS, the magnetic lines of force expand, causing the magnetic field to cut across the sensor's windings (5). This, in turn causes current to flow through the WSS circuit in one direction. When the exciter ring tooth moves away from the sensor tip, the magnetic lines of force collapse cutting the winding in the opposite direction. This causes the current to flow in the opposite direction. Every time a tooth of the exciter ring passes the tip of the WSS, an AC signal is generated current. Each AC signal (positive to negative signal or squarewave) is interpreted by the ABM. It then compares the frequency of the sinewave to a time value to calculate vehicle speed. The ABM continues to monitor the frequency to determine a deceleration rate that would indicate a possible wheel-locking tendency.

Scheme 253

The signal strength of any magnetic induction sensor is directly affected by

1. Magnetic field strength; the stronger the magnetic field, the stronger the signal
2. Number of windings in the sensor; more windings provide a stronger signal
3. Exciter ring speed; the faster the exciter ring/tone wheel rotates, the stronger the signal will be
4. Distance (3) "air gap" between the exciter ring teeth and WSS the closer the WSS is to the exciter ring/tone wheel, the stronger the signal will be.

The WSS is not adjustable. A clearance specification has been established for manufacturing tolerances. If the clearance is not within these specifications, then either the WSS or other components may be damaged. The clearance between the WSS and the exciter ring is 0.005 - 0.050 in.

The assembly plant performs a "Rolls Test" on every vehicle that leaves the assembly plant. One of the test performed is a test of the WSS. To properly test the sensor, the assembly plant connects test equipment to the Data Link Connector (DLC). This connector is located to the right of the steering column and attached to the lower portion of the instrument panel. The rolls test terminal is spliced to the WSS circuit. The vehicle is then driven on a set of rollers and the WSS output is monitored for proper operation.

Scheme 254

1. Remove the front rotor (Refer to «ROTOR»(ref-163273-S11224058792004062400000) ).
2. Remove the wheel speed sensor mounting bolt (1) from the hub (3).
3. Remove the wheel speed sensor (2) from the hub (3).
4. Remove the wiring from the clips and disconnect the electrical connector.

Scheme 255

1. Install the wiring to the clips and Reconnect the electrical connector.
2. Install the wheel speed sensor (2) to the hub (3).
3. Install the wheel speed sensor mounting bolt (1) to the hub (3). Tighten the bolt to 21 N.m (190 in. lbs.).
4. Install the front rotor and brake caliper assembly (Refer to «ROTOR»(ref-163273-S11224058792004062400000) ).

Scheme 256

1. Raise the vehicle on a hoist.
2. Disconnect the wheel speed sensor electrical connector (3).
3. Remove the mounting bolt (1) from the sensor (4).
4. Remove the sensor (4) from the brake caliper adapter (2).

Scheme 257

1. Raise the vehicle on a hoist.
2. Disconnect the sensor wire harness.
3. Remove the brake line mounting nut and remove the brake line from the sensor stud (2).
4. Remove the mounting stud (2) from the sensor (1) and shield.
5. Remove the sensor (1) and shield from the differential housing (3).

Scheme 258

1. Insert the wheel speed sensor (4) in the brake caliper adapter (2).
2. Install the sensor mounting bolt (1) and tighten to 24 N.m (200 in. lbs.).
3. Reconnect the electrical wiring connector (3) to the sensor (4).
4. Lower the vehicle.

Scheme 259

1. Install the O-ring on the sensor (1) (if removed).
2. Insert the sensor (1) in the differential housing (3).
3. Install the sensor shield.
4. Install the sensor mounting stud (2) and tighten to 24 N.m (200 in. lbs.).
5. Install the brake line on the sensor stud (2) and install the nut.
6. Connect the harness to the sensor. Be sure the seal is securely in place between the sensor and the wiring connector.
7. Lower the vehicle.

DESCRIPTION - ELECTRONIC VARIABLE BRAKE PROPORTIONING

Vehicles equipped with ABS use electronic variable brake proportioning (EVBP) to balance front-to-rear braking. The EVBP is used in place of a rear proportioning valve. The EVBP system uses the ABS system to control the slip of the rear wheels in partial braking range. The braking force of the tear wheels is controlled electronically by using the inlet and outlet valves located in the Hydraulic Control Unit (HCU).

OPERATION - ELECTRONIC VARIABLE BRAKE PROPORTIONING

EVBP is able to decrease, hold and increase rear brake pressure without activating full ABS control. Upon entry into EVBP the inlet valve for the rear brake circuit is switched on so that the fluid supply from the master cylinder is shut off. In order to decrease the rear brake pressure, the outlet valve for the rear brake circuit is pulsed. This allows fluid to enter the low pressure accumulator (LPA) in the hydraulic control unit (HCU) resulting in a drop in fluid pressure to the rear brakes. In order to increase the rear brake pressure, the outlet valve is switched off and the inlet valve is pulsed. This increases the pressure to the rear brakes.

The EVBP will remain functional during many ABS fault modes. If both the red BRAKE and amber ABS warning indicators are illuminated, the EVBP may not be functioning.

The HCU consists of a valve body, pump motor, low pressure accumulators, inlet valves, outlet valves and noise attenuators.

Accumulators in the valve body store extra fluid released to the system for ABS mode operation. The pump provides the fluid volume needed and is operated by a DC type motor. The motor is controlled by the ABM.

The valves modulate brake pressure during antilock braking and are controlled by the ABM.

The HCU provides three channel ABS or four channel With Traction Control pressure control to the front and rear brakes. One channel controls the rear wheel brakes in tandem ABS . The two remaining channels control the front wheel brakes individually.

During antilock braking, the solenoid valves are opened and closed as needed.

During normal braking, the HCU solenoid valves and pump are not activated. The master cylinder and power booster operate the same as a vehicle without an ABS brake system.

Note. The three modes mentioned below do occur but not necessarily in the order listed every time.

During antilock braking, solenoid valve pressure modulation occurs in three stages, pressure increase, pressure hold, and pressure decrease. The valves are all contained in the valve body portion of the HCU.