Operation CHARM: Car repair manuals for everyone.
Home >> Ford Truck >> 2010 >> Ranger 2WD V6-4.0L >> Repair and Diagnosis >> Brakes and Traction Control >> Antilock Brakes / Traction Control Systems >> Testing and Inspection >> Initial Inspection and Diagnostic Overview >> Principles of Operations

Principles of Operations




Anti-Lock Control

Principles of Operations

Anti-Lock Braking

The ABS module uses a Hydraulic Control Unit (HCU) to prevent the wheels from locking up during a braking event. The HCU contains several solenoid-controlled valves, a pump motor, an accumulator and several sensors. The fluid pressure is transmitted through 4 normally open inlet valves inside the HCU, through the outlet ports of the HCU and finally to the brake calipers. One circuit of the brake master cylinder feeds the front brakes while the other circuit feeds the rear brakes. If the ABS module senses that a wheel is about to lock, based on wheel speed sensor data, the inlet valve will pulse closed, preventing more fluid from entering that circuit. The ABS module then reads the sensor signal from the affected wheel again. If the wheel is still decelerating, the normally closed outlet valve for that circuit is opened. This allows a controlled amount of hydraulic pressure in the brake caliper to be relieved into the HCU accumulator. Once the speed of the affected wheel matches the speeds of the other wheels, the ABS module returns the valves to their normal condition, allowing fluid flow to the affected brake caliper.

The ABS module is self-monitoring and will carry out self-tests after the ignition key is turned to the RUN position, after an ABS stop and after an AdvanceTrac(R) system activation. When the ignition switch is turned to the RUN position, the ABS module will carry out a preliminary electrical check of the wheel speed sensors and their circuits by sending voltage through the sensor and checking for the voltage to return. When the vehicle is traveling at speeds above 21 km/h (13 mph) and the brake pedal is not being pressed, the HCU pump motor will be commanded ON for approximately 0.5 second to check pump motor operation. Also, during all phases of operation while the vehicle is in motion, the ABS module checks for correct operation of the wheel speed sensors by comparing wheel speed input to other sensor input. Depending on the nature of the malfunction detected, the ABS module will deactivate the anti-lock control system and send a message over the High Speed Controller Area Network (HS-CAN) bus to the Instrument Cluster (IC). When the IC receives this message, it will illuminate the yellow ABS warning indicator and/or (if equipped) the stability/traction control message center indicator (sliding-car icon).


Electronic Brake Distribution (EBD)

On initial application of the brake pedal, full pressure is applied to the rear brakes. The ABS module then uses wheel speed input to calculate an estimated rate of deceleration. Once vehicle deceleration exceeds a predetermined threshold, the ABS module closes the appropriate isolation valves in the HCU to hold the rear brake pressure constant while allowing the front brake pressure to build. This creates a balanced braking condition between the front and rear wheels and minimizes the chance of rear wheel lockup during hard braking. As the vehicle decelerates, the valves are opened to increase the rear brake pressure in proportion to the front brake pressure.

Electronic Brake Distribution (EBD) will be disabled if there are 3 or more wheel speed sensor DTCs present in the ABS module. When EBD is disabled, the red brake warning indicator, the yellow ABS warning indicator and (if equipped) the sliding-car icon will be illuminated.


AdvanceTrac(R) with Roll Stability Control (RSC(R))

The AdvanceTrac(R) with Roll Stability Control (RSC(R)) system provides the following stability enhancement features for certain driving situations:

- Traction Control System - helps to avoid excessive drive-wheel spin and loss of traction.
- Electronic Stability Control (ESC) - helps to avoid skids and lateral slides.
- RSC(R) - helps to avoid vehicle roll-over.

Traction Control System

The traction control system utilizes ABS and the PCM to minimize wheel spin during acceleration. When the ABS module detects a wheel spinning excessively, it commands the HCU to modulate brake pressure to the appropriate brake caliper. This is accomplished by opening and closing the appropriate solenoid valves inside of the HCU while the hydraulic pump motor is activated. At the same time, the ABS module sends a message over the HS-CAN bus that a traction control event is taking place. When the IC receives this message, it will flash the sliding-car icon. If the event is severe enough, the ABS module will also send a message to the PCM over the HS-CAN bus to assist with traction control. When the PCM receives this message, it will adjust engine timing and decrease fuel injector pulses. Once the affected wheel returns to normal speed, the ABS module returns the solenoid valves in the HCU to their normal position, deactivates the hydraulic pump motor and sends another message over the HS-CAN bus indicating that the traction event has ended. The PCM returns engine timing and fuel injectors to normal operation and the IC extinguishes the sliding-car icon.

Certain DTCs in the ABS module will disable the traction control system. Depending on the DTCs present, the yellow ABS warning indicator and/or the sliding-car icon will be illuminated.

Electronic Stability Control (ESC) and Roll Stability Control (RSC(R)) Systems

The ESC and RSC(R) systems are controlled by the ABS module and use the same wheel speed sensors and tone rings that are used for anti-lock braking. The ESC and RSC(R) systems also use input from the steering wheel rotation sensor, the stability control sensors (yaw rate, roll rate, longitudinal acceleration and lateral acceleration) which are internal to the Restraints Control Module (RCM) and information from other modules sent over the HS-CAN bus to help maintain vehicle stability.

The ABS module uses the various sensors to continuously monitor vehicle roll motion and direction of travel relative to the driver's intended course. If the ABS module determines from all these inputs that the vehicle is unable to travel in the intended direction or that a condition exists for a potential roll-over event, it modulates brake pressure to the appropriate brake caliper(s) by opening and closing the appropriate solenoid valves inside the HCU while the hydraulic pump motor is activated. At the same time, the ABS module sends a message over the HS-CAN bus that a stability event is taking place. When the IC receives this message, it will flash the sliding-car icon. During a stability event, conditions may require the involvement of the PCM to limit engine torque like it does for traction control. Once the stability condition has been corrected, the ABS module sends another message over the HS-CAN bus indicating that the event has ended. The PCM returns engine timing and fuel injectors to normal operation and the IC extinguishes the sliding-car icon.

Certain DTCs being present in the ABS module may disable the ESC and RSC(R) systems. Depending on the DTCs present, the yellow ABS warning indicator and/or the sliding-car icon will be illuminated.


Stability/Traction Control Switch

Unlike conventional ABS, the individual systems of AdvanceTrac(R) with RSC(R) can be deactivated by the driver through the stability/traction control switch. The switch is hard-wired to the IC and when pressed, sends a ground signal to the IC. The IC then sends a message over the HS-CAN bus indicating that the driver has requested that the system be deactivated and illuminates the sliding-car OFF icon. The circumstances present when the switch is pressed and the duration of the button press will determine what systems are disabled.

- Button pressed momentarily - only traction control is disabled and the sliding-car OFF icon will illuminate solidly.
- Button pressed and held for more than 5 seconds with vehicle speed under 56 km/h (35 mph) - RSC(R), ESC and traction control are all disabled and the sliding-car OFF icon will extinguish for 3 seconds and then illuminate solidly.
- Button pressed after deactivation - all 3 systems will be enabled and the sliding-car OFF icon will not be illuminated.
- Vehicle speed exceeds 56 km/h (35 mph) after the button is pressed and held for more than 5 seconds - RSC(R) and ESC will be enabled but traction control will be disabled. The sliding-car OFF icon will remain illuminated solidly.

If the switch is pressed and held for more than 30 seconds, a DTC will be set in the ABS module.

Once disabled, the systems will remain in that state until the driver presses the switch again, the ignition is cycled or the vehicle speed reaches or exceeds 56 km/h (35 mph). Once the vehicle speed reaches or exceeds 56 km/h (35 mph), RSC(R) and ESC will re-activate but traction control will remain deactivated.

Stability/Traction Control Message Center Indicators (Sliding-Car Icon and Sliding-Car OFF Icon)

Status of the traction control, ESC and RSC(R) system is indicated by a sliding-car icon and a sliding-car OFF icon located in the IC message center. The sliding-car OFF icon will illuminate solidly when the driver disables one or more of the systems through the use of the stability/traction control switch. If there are DTCs present in the ABS module directly related to the AdvanceTrac(R) with RSC(R) system. Also, the sliding-car icon will flash when one or more of the systems is currently active.


Stability Control Sensors

The stability control sensors for the AdvanceTrac(R) with RSC(R) system consist of the yaw rate sensor, roll rate sensor, lateral accelerometer and longitudinal accelerometer. The sensors are housed in the RCM which sends sensor information to the ABS module over a dedicated CAN bus. If any of the sensors are defective, a new RCM must be installed.

- The yaw rate sensor measures the relative vehicle motion about the vertical axis through its center of gravity.
- The roll rate sensor measures the rate of rotation along the front to rear horizontal axis.
- The lateral accelerometer measures the acceleration that corresponds to the force involved when the vehicle moves sideways.
- The longitudinal accelerometer measures the acceleration corresponding to the force involved when the vehicle moves forward and rearward in the horizontal plane, along the centerline of the vehicle's front and rear wheels.

Lateral acceleration has 2 forms. The first is the centrifugal acceleration that is generated when the vehicle travels around in a circle. The second is the acceleration due to gravity. On level ground there is no contribution from this acceleration. However, if the vehicle is parked sideways on a bank or incline, the sensor measures some lateral acceleration due to gravity, even though the vehicle is not moving.


Steering Wheel Rotation Sensor

The steering wheel rotation sensor uses an optical sensor and a slotted wheel to measure the rate of rotation (angle) of the steering wheel. The steering wheel rotation sensor uses 2 signal lines to transmit information to the ABS module about whether the steering wheel is being turned left or right and how far it is being turned. The steering wheel rotation sensor does not indicate the absolute position of the steering wheel relative to straight-ahead. The ABS module learns this position by comparing the steering wheel position with other signals and storing the position it has learned. The module confirms this position and modifies it as necessary during every new driving cycle.

ABS Module Configuration

Module configuration is a scan tool process which configures specific vehicle settings in a new module. If installing a new ABS module and/or a new HCU, the ABS module must be configured. To configure the ABS module, refer to Programmable Module Installation (PMI) in Information Bus. Programming and Relearning

ABS Module Calibration

The calibration procedure is required for the ABS module to learn the "zero-position" of the stability control sensors.

To calibrate the ABS module, connect the scan tool and carry out the IVD Initialization sequence, following the scan tool directions. The vehicle must be on a level surface and must not be moving during calibration. If a DTC is retrieved after calibration, refer to the ABS Module DTC Chart. [1][2]Diagnostic Trouble Code Descriptions

pro multis · About Operation CHARM