Anti-Lock Control - Traction Control Land Rover Range Rover L322

SPECIFICATIONS

TORQUE SPECIFICATIONS

COMPONENT LOCATION - SHEET 1 OF 2

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

Scheme 1

COMPONENT LOCATION - SHEET 2 OF 2

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

Scheme 2

OVERVIEW

The anti-lock control - traction control system features a Bosch ESP®plus8.1 modulator, which is an integrated four-channel hydraulic control unit (HCU) and anti-lock brake system (ABS) module.

The anti-lock brake system (ABS) module is connected to the high speed controller area network (CAN) bus, and actively interacts with other vehicle system control modules and associated sensors to receive and transmit current vehicle operating information.

When required, the anti-lock brake system (ABS) module will actively intervene and operate the hydraulic control unit (HCU) during braking or vehicle maneuvers to correct the vehicle attitude, stability, traction or speed. During incidents of vehicle correction, the anti-lock brake system (ABS) module may also request the engine control module (ECM) 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

1. DSC switch.
2. HDC switch.
3. Four wheel speed sensors.
4. Steering angle sensor.
5. Yaw rate and lateral acceleration sensor.
6. Stoplamp switch.
7. Instrument cluster warning indicators.
8. Integrated hydraulic control unit (HCU) and anti-lock brake system (ABS) module.

The anti-lock control - traction control system provides the following brake functions that are designed to assist the vehicle or aid the driver

1. anti-lock brake system (ABS).
2. ARM (active roll mitigation).
3. CBC (corner brake control).
4. DSC.
5. EBD (electronic brake force distribution).
6. Electronic brake prefill.
7. ETC (electronic traction control).
8. EBA (emergency brake assist).
9. EDC (engine drag-torque control).
10. EUC (enhanced understeer control).
11. Gradient acceleration control.
12. Gradient release control.
13. HDC.
14. Hill start assist.
15. 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.

Scheme 3

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

1. If the vehicle needs to be rocked out of a hollow or a soft surface.
2. Driving on loose surfaces or with snow chains.
3. Driving in deep sand, snow or mud.
4. 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 anti-lock brake system (ABS) module. With the first press of the DSC switch, the anti-lock brake system (ABS) module disables the DSC functions. When the DSC switch is pressed again, the anti-lock brake system (ABS) module re-enables the DSC functions. The DSC switch must be pressed for a minimum of 0.3 s for the anti-lock brake system (ABS) 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 anti-lock brake system (ABS) 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 diagnostic trouble code (DTC) is stored in the anti-lock brake system (ABS) module.

Even if DSC is deselected, driving maneuvers with extreme yaw or lateral acceleration may trigger DSC activity to assist vehicle stability.

Scheme 4

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 anti-lock brake system (ABS) module. With the first press and release of the HDC switch, the anti-lock brake system (ABS) module enables operation of the HDC function. When the HDC switch is pressed and released again, the anti-lock brake system (ABS) 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 diagnostic trouble code (DTC) is stored in the anti-lock brake system (ABS) module.

Scheme 5

An active wheel speed sensor is installed in each wheel hub to provide the anti-lock brake system (ABS) 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 anti-lock brake system (ABS) module. When the ignition switch is on, the anti-lock brake system (ABS) 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 anti-lock brake system (ABS) module.

The anti-lock brake system (ABS) module outputs the individual wheel speeds and the vehicle speed on the high speed controller area network (CAN) bus for use by other systems. The quality of the vehicle speed signal is also broadcast on the high speed controller area network (CAN) 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 anti-lock brake system (ABS) module monitors the wheel speed sensor circuits for faults. If a fault is detected the anti-lock brake system (ABS) module stores a diagnostic trouble code (DTC) and illuminates the appropriate warning indicators, depending on the system functions affected (DSC/ETC, anti-lock brake system (ABS), emergency brake assist (EBA)/electronic brake force distribution (EBD), HDC). A warning chime sounds and a related message is shown in the message center. Refer to Information and Message Center .

Since the wheel speed sensors are active devices, a return signal is available when the road wheels are not turning, which enables the anti-lock brake system (ABS) 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 controller area network (CAN) 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 controller area network (CAN) bus together with a quality factor signal, and are used by the anti-lock brake system (ABS) 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

1. The vehicle is traveling in a straight line.
2. The vehicle speed is between 20 and 25 km/h (12.5 and 15.6 mph).
3. The transfer box is in high range.
4. The brake pedal is not pressed.
5. There is no anti-lock brake system (ABS), 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 diagnostic trouble code (DTC). 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.

Scheme 6

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 anti-lock brake system (ABS) 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 central junction box (CJB). Yaw rate and lateral acceleration values are transmitted to the anti-lock brake system (ABS) module on a private high speed controller area network (CAN) bus. In addition to using the inputs for brake control functions, the anti-lock brake system (ABS) module also broadcasts the yaw rate and lateral acceleration values on the vehicle high speed controller area network (CAN) bus for use by other systems.

The anti-lock brake system (ABS) 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 anti-lock brake system (ABS) module stores a related diagnostic trouble code (DTC) and transmits a high speed controller area network (CAN) 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. Refer to Information and Message Center .

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 engine control module (ECM). One of the outputs is also supplied to the central junction box (CJB), for operation of the stoplamps. The engine control module (ECM) broadcasts the status of the stoplamp switch on the high speed controller area network (CAN) for use by other systems.

Power for the stoplamp switch is provided by an ignition feed from the central junction box (CJB). 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.

Scheme 7

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 hydraulic control unit (HCU) is a four-channel unit that modulates the supply of hydraulic pressure to the brakes under control of the anti-lock brake system (ABS) module.

The hydraulic control unit (HCU) is installed in the engine compartment, on three mounting bushes attached to the driver side inner fender. Hydraulic pipes connect the hydraulic control unit (HCU) to the master cylinder and the brake calipers. Refer to Hydraulic Brake Actuation .

The primary and secondary outlets of the master cylinder are connected to the primary and secondary circuits within the hydraulic control unit (HCU). The primary circuit in the hydraulic control unit (HCU) has separate outlet ports to the front brakes. The secondary circuit in the hydraulic control unit (HCU) has separate outlet ports to the rear brakes. Each of the circuits in the hydraulic control unit (HCU) contains the following components to control the supply of hydraulic pressure to the brakes

1. A normally open, solenoid operated, pilot valve, to enable active braking.
2. A normally closed, solenoid operated, priming valve, to connect the brake fluid reservoir to the return pump during active braking.
3. A return pump to generate hydraulic pressure for active braking, and return brake fluid to the reservoir.
4. Normally open, solenoid operated, inlet valves and normally closed, solenoid operated, outlet valves, to modulate the hydraulic pressure in the individual brakes.
5. An accumulator and a relief valve to allow the fast release of pressure from the brakes.
6. Filters to protect the components from contamination.

The primary circuit also incorporates a pressure sensor to provide the anti-lock brake system (ABS) module with a hydraulic pressure signal.

Contact pins on the hydraulic control unit (HCU) mate with contacts on the anti-lock brake system (ABS) module to provide the electrical connections from the anti-lock brake system (ABS) module to the return pump motor and the pressure sensor. The solenoids that operate the valves are installed in the anti-lock brake system (ABS) module.

A replacement hydraulic control unit (HCU) 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 hydraulic control unit (HCU) and brake circuits.

The hydraulic control unit (HCU) has three operating modes: Normal/electronic brake force distribution (EBD), anti-lock brake system (ABS) 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 anti-lock brake system (ABS) module determines that electronic brake force distribution (EBD) 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 anti-lock brake system (ABS) module determines that anti-lock brake system (ABS) 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 anti-lock brake system (ABS) 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 anti-lock brake system (ABS) braking, for example: DSC, emergency brake assist (EBA), ETC, HDC and dynamic application of the parking brake.

For active braking, the anti-lock brake system (ABS) 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 anti-lock brake system (ABS) 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 anti-lock brake system (ABS) module controls the brake functions using the hydraulic control unit (HCU) to modulate hydraulic pressure to the individual wheel brakes.

The anti-lock brake system (ABS) module is attached to the hydraulic control unit (HCU), on the driver side inner fender in the engine compartment. A multipin connector provides the electrical interface between the anti-lock brake system (ABS) module and the vehicle wiring.

CONTROL DIAGRAM

Note. A = Hardwired; D = High speed controller area network (CAN) bus; J = Diagnostic ISO 9141 K line; V = Private controller area network (CAN) bus.

Scheme 8

ANTI-LOCK BRAKE SYSTEM

Anti-lock brake system (ABS) controls the speed of all road wheels to ensure optimum wheel slip when braking at the adhesion limit. This prevents the wheels from locking in order to retain effective steering control of the vehicle.

On the front axle, the brake pressure is modulated separately for each wheel. On the rear axle, brake pressure is modulated by select low. Select low applies the same pressure to both rear brakes, with the pressure level being determined by the wheel on the lower friction surface. This maintains rear stability on split friction surfaces.

ACTIVE ROLL MITIGATION

The ARM function uses the brake system and engine torque control to attempt to restore vehicle stability if the vehicle is forced into such a harsh maneuver that it risks tipping over.

The anti-lock brake system (ABS) module monitors driver inputs and vehicle behavior using various powertrain signals and inputs from the wheel speed sensors, steering angle sensor and the yaw-rate and lateral acceleration sensor. These are compared with modeled behavior and, if vehicle behavior reaches a given risk level, the anti-lock brake system (ABS) module initiates a reduction in engine power, or brakes one or more wheels sufficiently to correct the vehicle stability and assist the driver remain in control.

While the ignition is on, ARM is permanently enabled, even when DSC is selected off.

CORNER BRAKE CONTROL

CBC influences the brake pressures, below the DSC and anti-lock brake system (ABS) thresholds, to counteract the yawing moment produced when braking in a corner. CBC produces a correction torque by limiting the brake pressure on one side of the vehicle.

DYNAMIC STABILITY CONTROL

DSC uses the brakes and engine torque control to help maintain the lateral stability of the vehicle. While the ignition is on the DSC function is permanently enabled unless selected off by the DSC switch. Even if DSC is deselected, driving maneuvers with extreme yaw or lateral acceleration may trigger DSC activity to assist vehicle stability.

DSC enhances driving safety in abrupt maneuvers and in understeer or oversteer situations that may occur in a bend. The anti-lock brake system (ABS) module monitors the yaw-rate and lateral acceleration of the vehicle, and the steering input, then selectively applies individual brakes and signals for engine torque adjustments to reduce understeer or oversteer.

In general: in an understeering situation, the inner wheels are braked to counteract the yaw movement towards the outer edge of the bend. In an oversteering situation, the outer wheels are braked to prevent the rear end of the vehicle from pushing towards the outer edge of the bend.

The anti-lock brake system (ABS) module monitors the tracking stability of the vehicle using inputs from the wheel speed sensors, the steering angle sensor and the yaw-rate and lateral acceleration sensor. The tracking stability is compared with stored target data and, whenever the tracking stability deviates from the target data, the anti-lock brake system (ABS) module intervenes by applying the appropriate brakes. When the DSC function is active, the anti-lock brake system (ABS) module also signals the transmission control module (TCM) to prevent gear shifts, and the instrument cluster to flash the DSC warning indicator.

If necessary, the anti-lock brake system (ABS) module also signals

1. The engine control module (ECM), to reduce engine torque.
2. The transfer box control module, to adjust the locking torque of the center differential.
3. The active on-demand coupling module, to adjust the locking torque of the rear differential.

The DSC function overrides the differential locking torque requests from the terrain response system.

If DSC is selected off, a DSC system off message is displayed in the message center. Refer to Information and Message Center .

ELECTRONIC BRAKE FORCE DISTRIBUTION

electronic brake force distribution (EBD) limits the brake pressure applied to the rear wheels. When the brakes are applied, the weight transfer of the vehicle reduces the adhesion of the rear wheels on the road surface. This may cause the rear wheels to slip and make the vehicle unstable.

electronic brake force distribution (EBD) uses the anti-lock brake system (ABS) hardware to automatically optimize the pressure of the rear brakes, below the point where anti-lock brake system (ABS) intervention is normally invoked. Only the rear wheels are under electronic brake force distribution (EBD) control.

ELECTRONIC BRAKE PREFILL

Electronic brake prefill senses any rapid throttle lift off, activating a small brake hydraulic pressure build-up of approximately 3 to 5 bar (43.5 to 72.5 lbf/in 2 ) in anticipation of the brakes being applied. This gives a quicker brake pedal response and consequently slightly shorter stopping distances.

When the anti-lock brake system (ABS) module detects rapid throttle lift off (from the signals received from the engine control module (ECM) over the high speed controller area network (CAN) bus), it controls the hydraulic control unit (HCU) to apply a low brake pressure to assist in a quicker brake application.

ELECTRONIC TRACTION CONTROL

ETC attempts to optimize forward traction by reducing engine torque or braking a spinning wheel until traction is restored.

ETC is activated if an individual wheel speed is above that of the vehicle reference speed (positive slip) and the brake pedal is not pressed. The spinning wheel is braked, allowing the excess torque to be transmitted to the non spinning wheels through the drive line. If necessary, the anti-lock brake system (ABS) module also transmits a high speed controller area network (CAN) bus message to the engine control module (ECM) requesting a reduction in engine torque.

Torque reduction requests are for either a slow or fast response. A slow response requests a reduction of throttle angle; a fast response requests an ignition cut-off.

When the DSC function is selected off with the DSC switch, the engine torque reduction feature is disabled.

When the ETC function is active the anti-lock brake system (ABS) module also signals the transmission control module (TCM) to prevent gear shifts.

EMERGENCY BRAKE ASSIST

emergency brake assist (EBA) assists the driver during emergency braking situations by automatically maximizing the braking effort. There are two situations when the anti-lock brake system (ABS) module will invoke emergency brake assist (EBA)

1. When the brake pedal is pressed very suddenly.
2. When the brake pedal is pressed hard enough to bring the front brakes into anti-lock brake system (ABS) operation.

When the brake pedal is pressed very suddenly, the anti-lock brake system (ABS) module increases the hydraulic pressure to all of the brakes until the threshold for anti-lock brake system (ABS) operation is reached. This applies the maximum braking effort for the available traction. The anti-lock brake system (ABS) module monitors for the sudden application of the brakes using the stoplamp switch status broadcast on the high speed controller area network (CAN) by the engine control module (ECM), and from the pressure sensor within the hydraulic control unit (HCU). With the brake pedal pressed, if the rate of increase of hydraulic pressure exceeds the predetermined limit, the anti-lock brake system (ABS) module invokes emergency braking.

When the brake pedal is pressed hard enough to bring the front brakes into anti-lock brake system (ABS) operation, the anti-lock brake system (ABS) module increases the hydraulic pressure to the rear brakes up to the anti-lock brake system (ABS) threshold.

emergency brake assist (EBA) operation continues until the driver releases the brake pedal enough for the hydraulic pressure in the hydraulic control unit (HCU) to fall below a pre-determined threshold value stored in the anti-lock brake system (ABS) module.

ENGINE DRAG-TORQUE CONTROL

EDC prevents wheel slip caused by any of the following

1. A sudden decrease in engine torque when the accelerator is suddenly released.
2. A downshift using the CommandShift™.

When the anti-lock brake system (ABS) module detects the onset of wheel slip without the brakes being applied, it transmits a message to the engine control module (ECM) via the high speed controller area network (CAN) bus to request a momentary increase in engine torque.

ENHANCED UNDERSTEER CONTROL

Understeer logic control monitors the vehicle for understeer by comparing signals from the yaw rate and lateral acceleration sensor with signals from the steering angle sensor and wheel speed sensors.

When the anti-lock brake system (ABS) module detects the onset of understeer, it signals the engine control module (ECM) via the high speed controller area network (CAN) bus to request a decrease in engine torque. If required the anti-lock brake system (ABS) module will control the hydraulic control unit (HCU) to apply brake pressure to the inside rear wheel to correct the understeer. If the vehicle continues to understeer, enhanced understeer control is activated and uses multiple brakes (maximum of three brakes) to rapidly reduce the vehicle speed.

GRADIENT ACCELERATION CONTROL

Gradient acceleration control is an automatic feature and is always available when HDC is not selected.

When HDC is not selected, gradient acceleration control will intervene to limit downhill acceleration on a steep descent.

The feature uses generated brake pressure to control acceleration in situations where the driver could lose control of the vehicle on a steep incline.

Gradient acceleration control keeps the vehicle to a speed and throttle pedal dependent acceleration limit when the vehicle is moving in the intended direction of travel, for example

1. Descending an incline forwards, with D (drive) selected.
2. Descending an incline backwards, with R (reverse) selected.

When the vehicle is moving against the intended direction of travel, for example: descending a slope, but facing uphill with D selected, gradient acceleration control will prevent the vehicle accelerating above 5 km/h (3 mph) for up to 20-30 seconds to aid the driver in re-establishing control of the vehicle.

GRADIENT RELEASE CONTROL

Gradient release control is an automatic feature which is always available when HDC is selected.

If the vehicle is brought to a standstill on a slope using the foot brake, gradient release control will become active (except in the terrain response, sand program). Subsequently, when the foot brake is released gradient release control will automatically delay and graduate the brake release. This allows time for the foot to be moved from the brake pedal to the accelerator pedal so that the vehicle can move smoothly away.

When descending a hill, a similar brake hold and gradual release is employed to provide a smooth transition into HDC. Gradient release control operates in forward and reverse gears and requires no driver intervention.

HILL DESCENT CONTROL

HDC uses brake intervention to control vehicle speed and acceleration during low speed descents in off-road and low grip on-road conditions. Generally, equal pressure is applied to all four brakes, but pressure to individual brakes can be modified by the anti-lock brake system (ABS) and DSC functions to retain stability. Selection of the HDC function is controlled by the HDC switch and the terrain response rotary control located on the floor console. HDC operates in both high and low ranges, at vehicle speeds up to 50 km/h (31.3 mph).

Note. With the HDC function selected, HDC is operative even when the transmission is in the neutral. It is not recommended to drive the vehicle further than is absolutely necessary with HDC selected and the transmission in neutral.

HDC may be used in D, R and CommandShift 1 in high range, and in D, R and all CommandShift gears in low range. When in D, the transmission control module (TCM) will automatically select the most appropriate gear.

HDC can be selected at speeds up to 80 km/h (50 mph), but will only be enabled at speeds below 50 km/h (31.3 mph). When HDC is selected

1. At speeds up to 50 km/h (31.3 mph), the HDC information warning indicator is permanently illuminated if a valid gear is selected.
2. At speeds from between 50 to 80 km/h (31 to 50 mph) the HDC information warning indicator flashes and a message advising that the speed is too high is displayed in the message center. If the HDC switch is pressed while vehicle speed is more than 80 km/h (50 mph), the HDC information warning indicator will not illuminate and HDC will not be selected.
3. If the speed increases to 80 km/h (50 mph), the HDC function is switched off, the information warning indicator is extinguished, a warning chime sounds and a message advising that HDC has been switched off is displayed in the message center.

When HDC is enabled, the anti-lock brake system (ABS) module calculates a target deceleration value by comparing the set speed to the actual vehicle speed. The anti-lock brake system (ABS) module then operates the hydraulic control unit (HCU) in the active braking mode as required to achieve and maintain the target speed.

During active braking for HDC, the anti-lock brake system (ABS) module sends a high speed controller area network (CAN) message to the central junction box (CJB) to operate the stoplamps. Refer to Exterior Lighting .

Applying the foot brake during active braking may result in a pulse through the brake pedal.

The target speed varies between minimum and maximum values for each gear and transmission range, depending on driver input with the accelerator pedal. If the accelerator pedal is not operated, the anti-lock brake system (ABS) module adopts a default target speed.

LOW RANGE TARGET SPEEDS

HIGH RANGE TARGET SPEEDS

As well as varying the target speed with the accelerator pedal, the target speed may also be varied by pressing the speed control '+' and '-' buttons (where fitted). Refer to Speed Control .

During changes of target speed, the anti-lock brake system (ABS) module limits deceleration and acceleration to -0.5 m/s2 (-1.65 ft/s 2 ) and +0.5 m/s2 (+1.65 ft/s 2 ) respectively.

To provide a safe transition from active braking to brakes off, the anti-lock brake system (ABS) module invokes a fade out strategy that gradually releases the braking effort during active braking. The fade out strategy occurs if any of the following conditions are detected during active braking

1. HDC selected off with the HDC switch.
2. Failure of a component used by HDC, but not critical to the fade out function.
3. Accelerator pedal pressed when transmission is in neutral.
4. Brake overheat.

If fade out is invoked because of deselection or component failure, the HDC function is cancelled by the anti-lock brake system (ABS) module. If fade out is invoked because the accelerator pedal is pressed with the transmission in neutral, or because of brake overheat, the HDC function remains in standby and resumes operation when the accelerator pedal is released or the brakes have cooled.

The fade out strategy increases the target speed, at a constant acceleration rate of 0.5 m/s 2 (1.65 ft/s 2 ), until the maximum target speed is reached or until no active braking is required for 0.5 s. If the accelerator pedal is positioned within the range that influences target speed, the acceleration rate is increased to 1.0 m/s 2 (3.3 ft/s 2 ).

When fade out is invoked because of component failure, a warning chime is sounded, the HDC information warning indicator is extinguished and a message advising there is a fault is displayed in the message center.

When fade out is invoked because of brake overheat, a message advising that HDC is temporarily unavailable is displayed. At the end of fade out, the HDC information warning indicator flashes. The message is displayed, while HDC remains selected, until the brakes have cooled.

To monitor for brake overheat, the anti-lock brake system (ABS) module monitors the amount of braking activity and, from this, estimates the temperature of each brake. If the estimated temperature of any brake exceeds a preset limit, the anti-lock brake system (ABS) module invokes the fade out strategy. After the fade out cycle, the HDC function is re-enabled when the anti-lock brake system (ABS) module estimates that all of the brake temperatures are at less than 64% of the temperature limit.

When HDC is selected off, the instrument cluster message center displays a system off message.

HILL START ASSIST

Hill start assist is an automatic feature that operates in a similar manner to gradient release control, but does not require HDC to be active. The feature is not driver selectable and there is no indication to the driver when in operation.

On steep slopes, hill start assist will hold a portion of the driver generated brake pressure for a short time to allow the driver to move their foot from the brake pedal to the throttle pedal without the vehicle rolling back.

The system will release the brake pressure in a controlled manner, either after the timer has expired or if the driver has generated sufficient drive-torque to move the vehicle forward up the hill.

The timer function is controlled by the engine control module (ECM) and transmitted to the anti-lock brake system (ABS) module on the high speed controller area network (CAN) bus.

TRAILER STABILITY ASSIST

When the trailer electrical socket is connected, trailer stability assist operates automatically to enhance the existing DSC and terrain response functions of the vehicle when towing. The system detects sway movements caused by trailer oscillations at speeds in excess of 60 km/h (37 mph) and acts to eliminate them. It does this through braking and engine management. Braking management counterbalances the sway movement through symmetric and asymmetric braking, thereby slowing the vehicle and eliminating the oscillations. Engine management adapts engine torque output to support the braking management in stabilizing the vehicle and trailer.

Typical conditions when sway can occur include

1. Changing highway lanes.
2. Traversing a lengthy bend.
3. Acceleration.
4. Braking.

The capability of trailer stability assist to respond early to the beginning of trailer-sway makes the system almost unnoticeable under normal driving conditions and keeps the vehicle and trailer under safe control. Trailer stability assist requires no input from the driver and operates up to the maximum vehicle speed.

Trailer stability assist will not operate while DSC is switched off.

PRINCIPLE OF OPERATION

For additional information on the Anti-Lock Control - Traction Control system, refer to the relevant Description and Operation instructions in the workshop information.

INSPECTION AND VERIFICATION

1. Verify the customer concern.
2. Visually inspect for obvious mechanical or electrical faults. VISUAL INSPECTION Mechanical Electrical Tire size, condition and installation Wheel speed sensor condition and installation Steering Angle Sensor (SAS) condition and installation Yaw rate sensor and accelerometer condition and installation Hydraulic control unit (with attached ABS module) condition and installation Fuses Harnesses and connectors Warning lamp operation Wheel speed sensors Central Junction Box HDC switch DSC switch Stop lamp switch Yaw rate sensor and accelerometer Steering Angle Sensor (SAS) ABS module Controller Area Network (CAN) circuits
3. If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.
4. If the cause is not visually evident, check for Diagnostic Trouble Codes (DTCs) and refer to the DTC Index.

DTC INDEX

For a list of Diagnostic Trouble Codes (DTCs) that could be logged on this vehicle, please refer to Instructions 100-00. Refer to Diagnostic Trouble Code (DTC) Index - DTC: Module Name: Anti-Lock Braking System .

REMOVAL

Note. The hydraulic control unit (HCU) mounted to the ABS module cannot be serviced separately. If the HCU requires replacement, then the ABS module must be replaced as a complete assembly.

Note. Removal steps in this procedure may contain installation details.

Scheme 9

Scheme 10

Scheme 11

1. Disconnect the battery ground cable. Refer to «Specifications»(/land-rover/range-rover/l322-2009-2012/remont/charging-system/#battery-and-charging-system-general-information) .
2. Torque: 18 Nm
3. Torque: 9 Nm
4. Torque: 9 Nm

INSTALLATION

ALL VEHICLES

1. To install, reverse the removal procedure.

VEHICLES WITH STANDARD BRAKES

1. Bleed the braking system. Refer to «Brake System Bleeding - Vehicles With: Standard Brakes»(/land-rover/range-rover/l322-2009-2012/remont/brakes/#brake-system-general-information__brake-system-bleeding) .

VEHICLES WITH HIGH PERFORMANCE BRAKES

1. Bleed the braking system. Refer to «Brake System Bleeding - Vehicles With: High Performance Brakes»(/land-rover/range-rover/l322-2009-2012/remont/brakes/#brake-system-general-information__brake-system-bleeding-vehicles-with-high) .

Note. Removal steps in this procedure may contain installation details.

Scheme 12

Scheme 13

Scheme 14

1. Disconnect the battery ground cable. Refer to «Specifications»(/land-rover/range-rover/l322-2009-2012/remont/charging-system/#battery-and-charging-system-general-information) .
2. Raise and support the vehicle.
3. Remove the front wheel and tire. Torque: 140 Nm
4. Disconnect the wheel speed sensor electrical connector.
5. Remove the front wheel speed sensor. Torque: 8 Nm

1. To install, reverse the removal procedure. Using the approved Land Rover diagnostic system, clear the fault codes from the ABS ECU.

Note. Removal steps in this procedure may contain installation details.

Scheme 15

Scheme 16

1. Disconnect the battery ground cable. Refer to «Specifications»(/land-rover/range-rover/l322-2009-2012/remont/charging-system/#battery-and-charging-system-general-information) .
2. Raise and support the vehicle.
3. Refer to «Rear Fender Splash Shield»(/land-rover/range-rover/l322-2009-2012/remont/exteriorinterior-trim/#exterior-trim-and-ornamentation) .
4. Torque: 8 Nm

1. To install, reverse the removal procedure.
2. Configure the anti-lock brake system (ABS) module using the diagnostic tool.

See also:
• Information and Message Center
• Hydraulic Brake Actuation
• Exterior Lighting
• Speed Control
• Diagnostic Trouble Code (DTC) Index - DTC: Module Name: Anti-Lock Braking System
• Specifications
• Brake System Bleeding - Vehicles With: Standard Brakes
• Brake System Bleeding - Vehicles With: High Performance Brakes
• Rear Fender Splash Shield