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Home >> Dodge >> 2001 >> Neon L4-2.0L VIN C >> Repair and Diagnosis >> Brakes and Traction Control >> Antilock Brakes / Traction Control Systems >> Description and Operation >> Antilock Brake System Components >> Component Descriptions

Component Descriptions

FRONT WHEEL SPEED SENSOR
DESCRIPTION
The Mark 20e system uses two-wire Wheel Speed Sensors (WSS), known as active WSS. The sensors use an electronic principle known as magnetoresistive to help increase performance and durability. The sensors convert wheel speed into a small digital signal. A WSS is used at each wheel. The gear (tooth) type tone wheel serves as the trigger mechanism for each sensor. At each wheel of the vehicle there is one WSS and one tone wheel.








The front WSS are attached to bosses in the steering knuckle. The tone wheel is an integral part of the outboard Constant Velocity (CV) joint located in the front axle shaft.
WSS air gaps are not adjustable. The initial factory WSS air gap specification can be found in SPECIFICATIONS. Each WSS is serviced individually. The tone wheels are serviced as part of the drive shaft.

OPERATION
The Controller Antilock Brake (CAB) sends 12 volts to power an Integrated Circuit (IC) in the sensor. The IC supplies a constant 7 mA power supply to the CAB. The relationship of the tooth on the tone wheel to the permanent magnet in the sensor, signals the IC to enable a second 7 mA power supply. The output of the sensor, sent to the CAB, is a DC voltage signal with changing voltage and current levels. The ground for the IC and the current sense circuit is provided by the CAB.
When a valley of the tone wheel is aligned with the sensor, the voltage signal is approximately 0.8 volts and a constant 7 mA current is sent to the CAB. As the tone wheel rotates, the tooth shifts the magnetic field and the IC enables a second 7 mA current source. The CAB senses a voltage signal of approximately 1.6 volts and 14 mA. The CAB measures the amperage of the digital signal for each wheel. The resulting signal is interpreted by the Antilock Brake System (ABS) CAB as the wheel speed.

REAR WHEEL SPEED SENSOR
DESCRIPTION
The Mark 20e system uses two-wire Wheel Speed Sensors (WSS), known as active wheel speed sensors. The sensors use an electronic principle known as magnetoresistive to help increase performance and durability. The sensors convert wheel speed into a small digital signal. A WSS is used at each wheel. The gear (tooth) type tone wheel serves as the trigger mechanism for each sensor. At each wheel of the vehicle there is one WSS and one tone wheel.








The rear WSS are mounted through the disc brake adapter. The rear tone wheels are mounted to and rotate with the hub and bearing assemblies.
The WSS air gaps are not adjustable. The initial factory WSS air gap specification can be found in SPECIFICATIONS. Each WSS is serviced individually. The tone wheels are serviced as an assembly with the hub and bearing assemblies.

OPERATION
The Controller Antilock Brake (CAB) sends 12 volts to power an Integrated Circuit (IC) in the sensor. The IC supplies a constant 7 mA power supply to the CAB. The relationship of the tooth on the tone wheel to the permanent magnet in the sensor, signals the IC to enable a second 7 mA power supply. The output of the sensor, sent to the CAB, is a DC voltage signal with changing voltage and current levels. The ground for the IC and the current sense circuit is provided by the CAB.
When a valley of the tone wheel is aligned with the sensor, the voltage signal is approximately 0.8 volts and a constant 7 mA current is sent to the CAB. As the tone wheel rotates, the tooth shifts the magnetic field and the IC enables a second 7 mA current source. The CAB senses a voltage signal of approximately 1.6 volts and 14 mA. The CAB measures the amperage of the digital signal for each wheel. The resulting signal is interpreted by the Antilock Brake System (ABS) CAB as the wheel speed.

TONE WHEEL
DESCRIPTION
The tone wheel is used in conjunction with the Wheel Speed Sensors (WSS).

OPERATION
The tone wheel is used in conjunction with the Wheel Speed Sensors (WSS).

MASTER CYLINDER
DESCRIPTION





A vehicle equipped with Antilock Brake System (ABS) uses a different master cylinder than a vehicle that is not equipped with ABS. Vehicles equipped with ABS use a center port master cylinder with only two outlet ports.
The brake tubes from the primary and secondary outlet ports on the master cylinder go directly to the Integrated Control Unit (ICU).
The master cylinder mounts to the power brake booster in the same manner a non-ABS master cylinder does.
DESCRIPTION - HYDRAULIC CONTROL UNIT (HCU)

Integrated Control Unit (ICU):





The Hydraulic Control Unit (HCU) is mounted to the Controller Antilock Brake (CAB) as part of the Integrated Control Unit (ICU). The HCU controls the flow of brake fluid to the brakes using a series of valves and accumulators. A pump/motor is mounted on the HCU to supply build pressure to the brakes during an Antilock Brake System (ABS) stop.

VALVES AND SOLENOIDS
The valve block contains four inlet valves and four outlet solenoid valves. The inlet valves are spring-loaded in the open position and the outlet valves are spring-loaded in the closed position during normal braking. The fluid is allowed to flow from the master cylinder to the wheel brakes.
During an ABS stop, these valves cycle to maintain the proper slip ratio for each wheel. The inlet valve closes preventing further pressure increase and the outlet valve opens to provide a path from the wheel brake to the HCU accumulators and pump/motor. This releases (decays) pressure from the wheel brake, thus releasing the wheel from excessive slippage. Once the wheel is no longer slipping, the outlet valve is closed and the inlet valve is opened to reapply (build) pressure.
There are four other valves in the HCU. These four remaining valves are used for traction control. Two Traction Control (TC) valves, mounted in the HCU valve block, are normally in the open position and close only when the traction control is applied. There are also two shuttle valves which control pressure return to the master cylinder under ABS and TC conditions.
These TC valves are used to isolate the rear (non-driving) wheels of the vehicle from the hydraulic pressure that the HCU pump/motor is sending to the front (driving) wheels when TC is being applied. The rear brakes need to be isolated from the master cylinder when traction control is being applied so the rear wheels do not drag.

BRAKE FLUID ACCUMULATORS
There are two fluid accumulators in the HCU: one for the primary hydraulic circuit, and one for the secondary hydraulic circuit. Each hydraulic circuit uses a 3 cc accumulator.
The fluid accumulators temporarily store brake fluid that is removed from the wheel brakes during an ABS cycle. This stored fluid is used by the pump/motor to provide build pressure for the brake hydraulic system. When the antilock stop is complete, the accumulators are drained by the pump/motor.
There are two noise dampening chambers in the HCU on this vehicle equipped with traction control.

PUMP/MOTOR
There are two pump assemblies in the HCU: one for the primary hydraulic circuit, and one for the secondary hydraulic circuit. Both pumps are driven by a common electric motor. This DC-type motor is integral to the HCU and is controlled by the CAB.
The pump/motor provides the extra amount of brake fluid needed during antilock braking. Brake fluid is released to the accumulators when the outlet valve is opened during an antilock stop. The pump mechanism consists of two opposing pistons operated by an eccentric camshaft. In operation, these pistons are used to purge fluid from the accumulators back into the master cylinder circuits. When the antilock stop is complete, the pump/motor drains the accumulators.
The pump motor is also used to build pressure when the system goes into traction control mode.
The CAB may turn on the pump/motor when an antilock stop is detected. The pump/motor continues to run during the antilock stop and is turned off after the stop is complete. Under some conditions, the pump/motor runs to drain the accumulators during the next drive-off.
The pump/motor is not a serviceable item; if it requires replacement, the HCU must be replaced.

OPERATION - HYDRAULIC CIRCUITS AND VALVES
The hydraulic valves control the flow of pressurized brake fluid to the wheel brakes during the different modes of Antilock Brake System (ABS) braking. The following paragraphs explain how this works. For purposes of explanation only, it is assumed that only the right front wheel is experiencing antilock braking; the diagrams show only the right front wheel in an antilock braking operation.

NORMAL BRAKING HYDRAULIC CIRCUIT, SOLENOID VALVE, AND SHUTTLE VALVE FUNCTION (ABS WITH TRACTION CONTROL)





The hydraulic diagram shows a vehicle with traction control in the normal braking mode. The diagram shows no wheel spin or slip occurring relative to the speed of the vehicle. The driver is applying the brake pedal; this builds pressure in the brake hydraulic system to engage the brakes and stop the vehicle. The hydraulic shuttle valve closes with every brake pedal application so pressure is not created at the inlet to the pump/motor.

ABS BRAKING HYDRAULIC CIRCUIT, SOLENOID VALVE, AND SHUTTLE VALVE FUNCTION (ABS WITH TRACTION CONTROL)





The hydraulic diagram shows the vehicle in the ABS braking mode. The diagram shows one wheel is slipping because the driver is attempting to stop the vehicle at a faster rate than is allowed by the surface on which the tires are riding.
- The hydraulic shuttle valve closes upon brake application so that the pump/motor cannot siphon brake fluid from the master cylinder.
- The normally open and normally closed valves modulate (build/decay) the brake hydraulic pressure as required.
- The pump/motor is switched on so that the brake fluid from the low pressure accumulators is returned to the master cylinder circuits.
- The brake fluid is routed to either the master cylinder or the wheel brake depending on the position of the normally open valve.

ABS TRACTION CONTROL HYDRAULIC CIRCUIT, SOLENOID VALVE, AND SHUTTLE VALVE FUNCTION (ABS WITH TRACTION CONTROL)





The hydraulic diagram shows the vehicle in the Traction Control (TC) mode. The diagram shows a drive wheel is spinning and brake pressure is required to reduce its speed.
- The normally open TC (ASR) valve is energized to isolate the brake fluid being pumped from the master cylinder and to isolate the driven wheel.
- The normally open TC (ASR) valve bypasses the pump output back to the master cylinder at a fixed pressure setting.
- The normally open and normally closed valves modulate (build/decay) the brake pressure as required to the spinning wheel.

ICU (INTEGRATED CONTROL UNIT)

DESCRIPTION
The Hydraulic Control Unit (HCU) and the Controller Antilock Brake (CAB) used with this Antilock Brake System (ABS) are combined (integrated) into one unit, which is called the Integrated Control Unit (ICU). The ICU is located on the driver's side of the vehicle, and is mounted to the left front frame rail below the master cylinder.
The ABS with traction control ICU consists of the following components: the CAB, eight (build/decay) solenoid valves (four inlet valves and four outlet valves), two hydraulic shuttle valves, two Traction Control (TC) valves, valve block, fluid accumulators, a pump, and an electric pump/motor.
The replaceable components of the ICU are the HCU and the CAB. No attempt should be made to service any components of the HCU or CAB.

OPERATION
For information of the Integrated Control Unit (ICU), refer to these individual components of the ICU:
- CONTROLLER ANTILOCK BRAKE (CAB)
- HYDRAULIC CONTROL UNIT (HCU)
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