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Home >> Land Rover >> 2012 >> Range Rover (LM) V8-5.0L >> Repair and Diagnosis >> Brakes and Traction Control >> Antilock Brakes / Traction Control Systems >> Description and Operation >> Part 1

Part 1





Anti-Lock Control - Traction Control

COMPONENT LOCATION - SHEET 1 OF 2

NOTE:
RHD (right-hand drive) vehicle shown, LHD (left-hand drive) similar.









COMPONENT LOCATION - SHEET 2 OF 2

NOTE:
LHD (left-hand drive) vehicle shown, RHD (right-hand drive) similar.









OVERVIEW
The anti-lock control - traction control system features a Bosch ESP(R)plus8.1 modulator, which is an integrated four-channel HCU (hydraulic control unit) and ABS (anti-lock brake system) module.
The ABS (anti-lock brake system) module is connected to the high speed CAN (controller area network) bus, and actively interacts with other vehicle system control modules and associated sensors to receive and transmit current vehicle operating information.
When required, the ABS (anti-lock brake system) module will actively intervene and operate the HCU (hydraulic control unit) during braking or vehicle maneuvers to correct the vehicle attitude, stability, traction or speed. During incidents of vehicle correction, the ABS (anti-lock brake system) module may also request the ECM (engine control module) to control engine power in order to further stabilize and correct the vehicle.
To provide full system functionality, the anti-lock control - traction control system comprises the following components:
- DSC switch.
- HDC switch.
- Four wheel speed sensors.
- Steering angle sensor.
- Yaw rate and lateral acceleration sensor.
- Stoplamp switch.
- Instrument cluster warning indicators.
- Integrated HCU (hydraulic control unit) and ABS (anti-lock brake system) module.
The anti-lock control - traction control system provides the following brake functions that are designed to assist the vehicle or aid the driver:
- ABS (anti-lock brake system).
- ARM (active roll mitigation).
- CBC (corner brake control).
- DSC.
- EBD (electronic brake force distribution).
- Electronic brake prefill.
- ETC (electronic traction control).
- EBA (emergency brake assist).
- EDC (engine drag-torque control).
- EUC (enhanced understeer control).
- Gradient acceleration control.
- Gradient release control.
- HDC.
- Hill start assist.
- Trailer stability assist.
The HDC function is enabled either manually using the HDC switch, or automatically by the terrain response system, in the ignition on and engine running power modes. All of the other brake functions are automatically enabled in the ignition on and engine running power modes. The DSC function can be selected off using the DSC switch.

DYNAMIC STABILITY CONTROL SWITCH









The DSC switch allows the DSC function to be selected off. Although Land Rover recommend that DSC is selected on for all normal driving conditions, it may be beneficial to de-select DSC to maximize traction under the following conditions:
- If the vehicle needs to be rocked out of a hollow or a soft surface.
- Driving on loose surfaces or with snow chains.
- Driving in deep sand, snow or mud.
- On tracks with deep longitudinal ruts.
The DSC switch is a non-latching switch installed in the center console switch pack. Pressing the DSC switch connects an ignition power feed to the ABS (anti-lock brake system) module. With the first press of the DSC switch, the ABS (anti-lock brake system) module disables the DSC functions. When the DSC switch is pressed again, the ABS (anti-lock brake system) module re-enables the DSC functions. The DSC switch must be pressed for a minimum of 0.3 s for the ABS (anti-lock brake system) module to react. The DSC function is re-enabled at the beginning of each ignition cycle.
The status of the DSC switch selection is shown by the DSC OFF warning indicator. The DSC OFF warning indicator is extinguished while DSC is selected on, and continuously illuminated while DSC is selected off.
A DSC switch request to disable DSC is ignored by the ABS (anti-lock brake system) module if the air suspension system has failed, or is in off-road height at speeds above 60 km/h (37.5 mph).
To guard against incorrect operation or a broken switch, if the input from the DSC switch is held high for more than one minute, a DTC (diagnostic trouble code) is stored in the ABS (anti-lock brake system) module.
Even if DSC is deselected, driving maneuvers with extreme yaw or lateral acceleration may trigger DSC activity to assist vehicle stability.

HILL DESCENT CONTROL SWITCH









The HDC switch controls the selection of the HDC function.
The HDC switch is a non-latching switch installed on the floor console, to the rear of the gear selector lever. Pressing and releasing the HDC switch momentarily connects an ignition power feed to the ABS (anti-lock brake system) module. With the first press and release of the HDC switch, the ABS (anti-lock brake system) module enables operation of the HDC function. When the HDC switch is pressed and released again, the ABS (anti-lock brake system) module disables operation of the HDC function.
To guard against incorrect operation or a broken switch, if the switch is pressed for more than 10 seconds no change of state occurs. If the input from the HDC switch is held high for more than one minute, a DTC (diagnostic trouble code) is stored in the ABS (anti-lock brake system) module.

WHEEL SPEED SENSORS









An active wheel speed sensor is installed in each wheel hub to provide the ABS (anti-lock brake system) module with a rotational speed signal from each road wheel. The head of each wheel speed sensor is positioned close to a 48 tooth sensor ring on the outer diameter of the constant velocity joint of the drive halfshaft. A flying lead connects each sensor to the vehicle wiring.
The wheel speed sensors each have a power supply connection and a signal connection with the ABS (anti-lock brake system) module. When the ignition switch is on, the ABS (anti-lock brake system) module supplies power to the wheel speed sensors and monitors the return signals. Any rotation of the drive halfshafts induces current fluctuations in the return signals which are converted into individual wheel speeds and the overall vehicle speed by the ABS (anti-lock brake system) module.
The ABS (anti-lock brake system) module outputs the individual wheel speeds and the vehicle speed on the high speed CAN (controller area network) bus for use by other systems. The quality of the vehicle speed signal is also broadcast on the high speed CAN (controller area network) bus. If all wheel speed signals are available to calculate vehicle speed from, the quality of the vehicle speed signal is set to 'data calculated within specified accuracy'. If one or more wheel speed sensors is faulty, the quality of the vehicle speed signal is set to 'accuracy outside specification'.
The ABS (anti-lock brake system) module monitors the wheel speed sensor circuits for faults. If a fault is detected the ABS (anti-lock brake system) module stores a DTC (diagnostic trouble code) and illuminates the appropriate warning indicators, depending on the system functions affected (DSC/ETC, ABS (anti-lock brake system), EBA (emergency brake assist)/EBD (electronic brake force distribution), HDC). A warning chime sounds and a related message is shown in the message center. For additional information, refer to Information and Message Center Description and Operation
Since the wheel speed sensors are active devices, a return signal is available when the road wheels are not turning, which enables the ABS (anti-lock brake system) module to check the sensors while the vehicle is stationary. In addition, the direction of travel of each wheel can be sensed. This information is broadcast on the high speed CAN (controller area network) bus for use by other systems.

STEERING ANGLE SENSOR









The steering angle sensor measures the steering wheel angle, and the rate of steering wheel angle speed. The measurements are output on the high speed CAN (controller area network) bus together with a quality factor signal, and are used by the ABS (anti-lock brake system) module and the rear differential control module for ARM, CBC and DSC operation.
The steering angle sensor is fixed to the pivot bracket of the steering column by three screws. A gear wheel in the steering angle sensor engages with a plastic drive collar fixed onto the lower shaft of the column. Inside the steering angle sensor, the gear wheel meshes with a gear train containing magnets. A multipin electrical connector provides the interface between the vehicle wiring and integrated circuits in the steering angle sensor.
The steering angle sensor operates with the MR (magneto resistive) effect to evaluate the direction of magnetic fields, and measure the angular position of the lower shaft to provide the steering wheel angle. When the steering wheel turns, the steering column lower shaft rotates the gear wheel within the steering angle sensor. The gear wheel drives the gear train and rotates the magnets located on the gears. The direction of the magnetic field is constantly monitored by the steering angle sensor and is converted into a steering wheel angle, and steering wheel angle speed.
The steering angle sensor performs a plausibility check of the steering wheel angle each time the following conditions co-exist:
- The vehicle is traveling in a straight line.
- The vehicle speed is between 20 and 25 km/h (12.5 and 15.6 mph).
- The transfer box is in high range.
- The brake pedal is not pressed.
- There is no ABS (anti-lock brake system), DSC or ETC activity.
The steering angle sensor uses inputs of wheel speed, yaw rate and lateral acceleration to determine when the vehicle is traveling in a straight line. When all of the conditions co-exist, the steering angle sensor checks the steering angle is between 0 ± 15°. If the steering angle is outside the limits on two successive checks, the steering angle sensor changes the quality factor signal to 'outside specification' for the remainder of the ignition cycle and stores a DTC (diagnostic trouble code). At the beginning of each ignition cycle the quality factor signal is reset to 'within specified accuracy'.
The status of the steering angle sensor is able to be determined using Land Rover approved diagnostic equipment.
If the steering angle sensor is renewed, the new sensor must be calibrated using Land Rover approved diagnostic equipment. The steering angle sensor must also be re-calibrated any time it is disturbed from the steering column, or if the upper and lower steering columns are separated.

YAW RATE AND LATERAL ACCELERATION SENSOR





The yaw rate and lateral acceleration sensor is located beneath the floor console and provides information of vehicle yaw rate and lateral acceleration to the ABS (anti-lock brake system) module. The sensor is internally damped to isolate it from body vibrations and is secured to the transmission tunnel with two bolts.
When the ignition is on, the yaw rate and lateral acceleration sensor receives a power feed from the CJB (central junction box). Yaw rate and lateral acceleration values are transmitted to the ABS (anti-lock brake system) module on a private high speed CAN (controller area network) bus. In addition to using the inputs for brake control functions, the ABS (anti-lock brake system) module also broadcasts the yaw rate and lateral acceleration values on the vehicle high speed CAN (controller area network) bus for use by other systems.
The ABS (anti-lock brake system) module monitors the yaw rate and lateral acceleration sensor for faults and can be interrogated using Land Rover approved diagnostic equipment. If a fault is detected, the ABS (anti-lock brake system) module stores a related DTC (diagnostic trouble code) and transmits a high speed CAN (controller area network) bus signal to the instrument cluster to illuminate the DSC, HDC and brake warning indicators. The instrument cluster will also sound a warning chime and display a DSC fault message in the message center. For additional information, refer to Information and Message Center Description and Operation

STOPLAMP SWITCH
The stoplamp switch is mounted in the brake pedal bracket and operated by the brake pedal. The stoplamp switch is a Hall effect switch with dual status outputs. Both of the outputs are supplied to the ECM (engine control module). One of the outputs is also supplied to the CJB (central junction box), for operation of the stoplamps. The ECM (engine control module) broadcasts the status of the stoplamp switch on the high speed CAN (controller area network) for use by other systems.
Power for the stoplamp switch is provided by an ignition feed from the CJB (central junction box). The power circuit is completed by a ground connection from the stoplamp switch to a ground header on the body.
When the brake pedal is not pressed, the outputs from the stoplamp switch are low, between 0 and 2 V. When the brake pedal is pressed the outputs are pulled high to between 8 V and battery voltage.

WARNING INDICATORS









The instrument cluster contains two types of warning indicator to display the operating status of the selected anti-lock control/traction control functions. The warning indicators provide a visual notification of either a system warning or system information to the driver.

HYDRAULIC CONTROL UNIT
The HCU (hydraulic control unit) is a four-channel unit that modulates the supply of hydraulic pressure to the brakes under control of the ABS (anti-lock brake system) module.
The HCU (hydraulic control unit) is installed in the engine compartment, on three mounting bushes attached to the driver side inner fender. Hydraulic pipes connect the HCU (hydraulic control unit) to the master cylinder and the brake calipers. For additional information, refer to Hydraulic Brake Actuation
The primary and secondary outlets of the master cylinder are connected to the primary and secondary circuits within the HCU (hydraulic control unit). The primary circuit in the HCU (hydraulic control unit) has separate outlet ports to the front brakes. The secondary circuit in the HCU (hydraulic control unit) has separate outlet ports to the rear brakes. Each of the circuits in the HCU (hydraulic control unit) contains the following components to control the supply of hydraulic pressure to the brakes:
- A normally open, solenoid operated, pilot valve, to enable active braking.
- A normally closed, solenoid operated, priming valve, to connect the brake fluid reservoir to the return pump during active braking.
- A return pump to generate hydraulic pressure for active braking, and return brake fluid to the reservoir.
- Normally open, solenoid operated, inlet valves and normally closed, solenoid operated, outlet valves, to modulate the hydraulic pressure in the individual brakes.
- An accumulator and a relief valve to allow the fast release of pressure from the brakes.
- Filters to protect the components from contamination.
The primary circuit also incorporates a pressure sensor to provide the ABS (anti-lock brake system) module with a hydraulic pressure signal.
Contact pins on the HCU (hydraulic control unit) mate with contacts on the ABS (anti-lock brake system) module to provide the electrical connections from the ABS (anti-lock brake system) module to the return pump motor and the pressure sensor. The solenoids that operate the valves are installed in the ABS (anti-lock brake system) module.
A replacement HCU (hydraulic control unit) is supplied pre-filled. After installation on the vehicle, the Land Rover approved diagnostic system must be used to operate the solenoid valves and the return pump to ensure correct bleeding of the HCU (hydraulic control unit) and brake circuits.

Schematic of Hydraulic Control Unit









The HCU (hydraulic control unit) has three operating modes: Normal/EBD (electronic brake force distribution), ABS (anti-lock brake system) braking and active braking.

Normal Braking/Electronic Brake Force Distribution Mode
Initially, all of the solenoid operated valves are de-energized. Operating the brake pedal produces a corresponding increase or decrease of pressure in the brakes, through the open pilot valves and inlet valves. If the ABS (anti-lock brake system) module determines that EBD (electronic brake force distribution) is necessary, it energizes the inlet valves for the brakes of the trailing axle, to isolate the brakes from any further increase in hydraulic pressure.

ABS Braking Mode
If the ABS (anti-lock brake system) module determines that ABS (anti-lock brake system) braking is necessary, it energizes the inlet and outlet valves of the related brake and starts the return pump. The inlet valve closes to isolate the brake from pressurized fluid; the outlet valve opens to release pressure from the brake into the accumulator and the return pump circuit. The reduced pressure allows the wheel to accelerate. The ABS (anti-lock brake system) module then operates the inlet and outlet valves to modulate the pressure in the brake to apply the maximum braking effort without locking the wheel. Control of the valves for each wheel takes place individually.

Active Braking Mode
The active braking mode is used to generate and control hydraulic pressure to the brakes for functions other than ABS (anti-lock brake system) braking, for example: DSC, EBA (emergency brake assist), ETC, HDC and dynamic application of the parking brake.
For active braking, the ABS (anti-lock brake system) module energizes the pilot valves and priming valves, starts the return pump and energizes all of the inlet valves. Brake fluid, drawn from the reservoir through the master cylinder and priming valve, is pressurized by the return pump and supplied to the inlet valves. The ABS (anti-lock brake system) module then operates the inlet valves and outlet valves, as required, to modulate the pressure in the individual brakes. Some noise may be generated during active braking.

ANTI-LOCK BRAKE SYSTEM MODULE
The ABS (anti-lock brake system) module controls the brake functions using the HCU (hydraulic control unit) to modulate hydraulic pressure to the individual wheel brakes.
The ABS (anti-lock brake system) module is attached to the HCU (hydraulic control unit), on the driver side inner fender in the engine compartment. A multipin connector provides the electrical interface between the ABS (anti-lock brake system) module and the vehicle wiring.
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