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Home >> Dodge and Ram >> 2007 >> Caravan V6-3.3L VIN E Flex Fuel >> Repair and Diagnosis >> Brakes and Traction Control >> Antilock Brakes / Traction Control Systems >> Description and Operation >> System Components

System Components

SYSTEM COMPONENTS

ABS
- anti-lock brake module (ABM)
- vacuum booster
- master cylinder
- integrated hydraulic control unit (HCU), 1 pump motor.
- 4 wheel speed sensor/tone wheel assemblies
- ABS warning indicator
- fuses and wiring harness
- fluid reservoir
- brake lamp switch
ABS With Traction Control
- CAB/ABM with Traction Control programming
- HCU with four additional control valves.
- TCS Switch
- TCS Indicator

ABS AND BRAKE WARNING INDICATORS
The amber ABS warning indicator is located in the instrument cluster. It is used to inform the driver that the antilock function has been turned off. The ABS warning indicator is controlled by the ABM. The ABM controls the lamp with a command over the PCI bus.

The ABS Warning Indicator will remain lit during every key cycle until a circuit or component fault is repaired and the ABM no longer detects the fault. After repair of a sensor signal fault or a pump motor fault, the ABM must sense all four wheels at 25 km/h (15 mph) before it will extinguish the ABS and TCS Indicator.

The Instrument Cluster will illuminate the ABS Warning Indicator if it loses communication with the ABM.

The red BRAKE warning indicator is also located in the instrument cluster. It can be activated in several ways. Application of the parking brake or a low fluid signal from the fluid level switch located in the master cylinder reservoir will cause the indicator to come on.

CONTROLLER ANTILOCK BRAKE/ANTI-LOCK BRAKE MODULE
The ABM is a microprocessor-based device that monitors wheel speeds and controls the antilock functions. The ABM contains two microprocessors that receive identical sensor signals and then independently process the information. The results are then compared to make sure that they agree. Otherwise, the ABM will turn off the antilock and turn on the ABS amber warning indicator.

The primary functions of the ABM are to:
- detect wheel locking tendencies
- control fluid pressure modulation to the brakes during antilock stop
- monitor the system for proper operation
- manage traction control functions
- provide communication to the DRBIII while in diagnostic mode
- store diagnostic information in non-volatile memory

The ABM continuously monitors the speed of each wheel. When a wheel locking tendency is detected, the ABM will command the appropriate valve to modulate brake fluid pressure in its hydraulic unit. Brake pedal position is maintained during an antilock stop by being a closed system. The ABM continues to control pressure in individual hydraulic circuits until a wheel locking tendency is no longer present. The ABM turns on the pump motor during an antilock stop.

The antilock brake system is constantly monitored by the ABM for proper operation. If the ABM detects a system malfunction, it can disable the antilock system and turn on the ABS warning indicator. If the antilock function is disabled, the system will revert to standard base brake system operation.

The ABM inputs include the following:
- diagnostic communication
- four wheel speed sensors
- three power feeds: valve, pump, and microprocessor
- brake lamp switch
- traction control switch

The ABM outputs include the following:
- ABS warning indicator actuation
- 12 volts supply to wheel speed sensors
- valve actuation
- diagnostic communication
- PCI bus communication
- traction control lamp illumination

HYDRAULIC CONTROL UNIT
The hydraulic control unit (HCU) contains the valve block assembly, and pump/motor assembly. The HCU is attached to the ABM.

Valve Block Assembly: The valve block assembly contains valves with four inlet valves and four outlet valves. The inlet valves are spring-loaded in the open position and the outlet valves are spring loaded in the closed position. During an antilock stop, these valves are cycled to maintain the proper slip ratio for each wheel. If a wheel detects slip, the inlet valve is closed to prevent and further pressure increase. Then the outlet valve is opened to release the pressure to the accumulators until the wheel is no longer slipping. Once the wheel is no longer slipping, the outlet valve is closed and the inlet valve is opened to reapply pressure. If the wheel is decelerating within its predetermined limits (proper slip ratio), the inlet valve will close to hold the pressure constant. On vehicles which are equipped with a traction control system, there are four additional valves, two isolate the master cylinder and two shuttle. During a traction control event the brakes are applied to reduce wheel slippage.

Pump Motor Assembly: The pump motor assembly provides the extra amount of fluid needed during antilock braking. The pump is supplied fluid that is released to the accumulators when the outlet valve is opened during an antilock stop. The pump is also used to drain the accumulator circuits after the antilock stop is complete. The pump is operated by an integral electric motor. This motor is controlled by the ABM. The ABM may turn on the pump motor when an antilock stop is detected. The pump continues to run during the antilock stop and is turned off after the stop is complete. Under some conditions, the pump motor will run to drain the accumulators during the next drive off. The ABM monitors the pump motor operation internally.

ABS SWITCHES/SENSORS
Master Cylinder: The master cylinder is a standard tandem compensating port design for ABS and non ABS systems. Traction control vehicles use a dual center port master cylinder. For proper traction control operation the standard master cylinder must not be used.

A fluid level switch is located in the master cylinder fluid reservoir. The switch closes when a low fluid level is detected. The fluid level switch turns on the brake warning indicator by grounding the indicator circuit. This switch does not disable the ABS system.

Wheel Speed Sensors and Tone Wheels: One active wheel speed sensor (WSS) is located at each wheel. The sensors use an electronic principle known as magneto-resistive to help increase performance, durability and low speed accuracy. The sensors convert wheel speed into a small digital signal. A toothed gear tone wheel serves as the trigger mechanism for each sensor.

The ABM sends 12 volts to power an Integrated Circuit (IC) in the sensor. The IC supplies a constant 7 mA signal to the ABM. The relationship of the tooth on the tone wheel to the permanent magnet in the sensor, signals the IC of the sensor to toggle a second 7 mA power supply on or off. The output of the sensor, sent to the ABM, is a DC voltage signal with changing voltage and current levels. The ABM monitors the changing amperage(digital signal) from each wheel speed sensor. The resulting signal is interpreted by the ABM as the wheel speed.

Because of internal circuitry, correct wheel speed sensor function cannot be determined by a continuity or resistance check through the sensor.

Correct antilock system operation is dependent on tone wheel speed signals from the wheel speed sensors. The vehicle's wheels and tires should all be the same size and type to generate accurate signals. In addition, the tires should be inflated to the recommended pressure for optimum system operation. Variation in wheel and tire size or significant variations in inflation pressure can produce inaccurate wheel speed signals; however, the system will continue to function when using the correct factory mini-spare.
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