Operating principles (Freelander 2)

Anti-lock braking system

ABS controls the speed of all wheels to ensure optimum wheel slip during braking while maintaining traction. Wheel locking is prevented to maintain control of the vehicle with effective steering. The front brake pressure is modulated individually for each wheel.

The rear brake pressure is modulated using the "select the lower" principle. The "select the lower" principle allows the same pressure to be applied to both rear brakes, corresponding to the pressure applied by the wheel located on the surface with lower friction. This maintains stability of the rear of the car when the wheels are located on surfaces with different coefficients of friction.

Cornering braking system

CBC influences the brake pressure, maintaining it below and within the ABS thresholds to counteract the yaw moment that occurs when braking in corners. CBC produces a corrective torque by limiting the brake pressure on one side of the vehicle.

Dynamic Stability Control

DSC uses the brakes and torque control of the powertrain to help maintain the lateral stability of the vehicle. When the ignition is on, the DSC function is always available unless deactivated using the DSC switch. Even when DSC is deactivated, maneuvers involving sharp yaw or lateral acceleration may cause RSC to act to help maintain vehicle stability.



DSC improves driving safety during abrupt manoeuvres and in understeer or oversteer situations that may occur when cornering. The ABS module monitors the yaw rate, lateral acceleration of the vehicle and the steering input and then selectively activates individual brakes and signals for torque adjustments in the powertrain to reduce understeer or oversteer.

As a rule:

• In an understeer situation, the inside wheels are braked to counteract the yaw towards the outside edge of the turn.
• In an oversteer situation, the outside wheels are braked to counteract the rear of the car moving towards the outside edge of the turn.

The ABS module monitors the vehicle's directional stability using input signals from the wheel speed sensors, steering angle sensor, lateral acceleration sensor and yaw rate sensor. The directional stability is compared with stored target data. Whenever the stability deviates from the target values, the ABS module intervenes by applying the appropriate brakes.

In an intervention situation the following interactions occur:

• Signal via high speed CAN bus to ECM to reduce engine torque.
• Signal via high speed CAN bus to the active clutch module to release the locking torque of the center clutch.
• Apply braking to the appropriate corner of the vehicle.

Electronic brake force distribution

EBD limits the amount of brake pressure applied to the rear wheels. When the brakes are applied, the weight of the vehicle is transferred forward, reducing the ability of the rear wheels to transmit braking force to the road surface. This can cause the rear wheels to slip and make the vehicle unstable.



EBD uses the anti-lock brake system hardware to automatically optimize rear brake pressure below the point where ABS would normally kick in.

NOTE: The EBD function controls the rear brakes only.

Electronic traction control system

ETC attempts to optimize forward traction by reducing engine torque or applying the brake on the slipping wheel until traction is restored.

ETC is activated when the speed of an individual wheel is above the vehicle reference speed (positive slip) and the brake pedal is not pressed. The brake is applied to the spinning wheel, allowing excess torque to be transferred through the transmission to the non-slipping wheels. If necessary, the ABS module also sends a message over the high-speed CAN bus to the ECM to request a reduction in engine torque.

When the DSC function is selected to be off using the DSC switch, the engine torque reduction function is switched off.

Emergency Brake Assist System

EBA assists the driver in emergency braking situations by automatically increasing the braking force. There are two situations in which the module causes EBA activation:

• When the brake pedal is pressed quickly.
• When the brake pedal is depressed hard enough to engage the ABS on the front brakes.

When the brake pedal is pressed quickly, the ABS module increases the hydraulic pressure in all brakes until the threshold for ABS operation is reached. This action provides maximum braking force for the available traction force. The ABS module monitors sudden activation of the brakes using input signals from the brake pedal switch and from the pressure sensor in the HCU. When the brake pedal is depressed, if the rate of increase in hydraulic pressure exceeds a preset limit value, the ABS module activates emergency braking.



When the brake pedal is pressed hard enough to engage the front brakes with ABS activation, the ABS module increases the hydraulic pressure supplied to the rear brakes up to the ABS threshold.

EBA operation continues until the driver releases the brake pedal sufficiently for the hydraulic pressure in the HCU to drop below the threshold value stored in the ABS module memory.

Engine braking torque control

EDC prevents wheel spin caused by any of the following:

• A sudden decrease in engine torque when the accelerator pedal is suddenly released.
• Sudden clutch engagement after downshifting on vehicles with manual transmission.
• Downshifting using CommandShift on vehicles with automatic transmission.

When the ABS module detects a wheel spin condition without applying the brakes, the ABS module sends a signal to the ECM via the high-speed CAN bus to request an immediate increase in engine torque.

Controlled descent system

HDC uses engine braking and brake intervention to control vehicle speed and acceleration on low-speed downhill slopes in off-road conditions and in low-traction off-road conditions. Normally, equal pressure is applied to all four brakes, but the pressure on individual brakes can be varied by the ABS and DSC systems to maintain vehicle stability. Selection of the HDC function is controlled by the HDC switch located on the floor console. HDC operates at vehicle speeds up to 50 km/h (31 mph).

WARNING: Improper use of the HDC function may compromise vehicle stability, resulting in dangerous and uncontrolled hill descents. Depressing the clutch pedal and/or driving with the transmission in neutral while the HDC system is active prevents engine braking from being applied to assist the vehicle. The brakes will overheat and initiate a reduced effectiveness strategy for HDC. In this condition, there will be no control of the vehicle while descending.

NOTE: When HDC is selected, it operates even when the clutch pedal is depressed or the transmission is in neutral. It is not recommended to continue driving the vehicle any further than absolutely necessary with HDC selected and the clutch pedal depressed or the transmission in neutral.

On vehicles with a manual transmission, HDC can only be used in first and reverse gear. Once the vehicle is in motion, the clutch pedal should be fully released. Do not select the 'N' position in the transmission while driving with HDC activated.

On vehicles with automatic transmission, HDC can only be used in the 'D', 'R' and CommandShift '1' positions. In the 'D' position, the TCM automatically selects the most appropriate gear. Do not select the 'N' position in the transmission while driving with HDC activated.

The HDC function can be selected at speeds up to 80 km/h, but will only be activated at speeds below 50 km/h.

When HDC is selected:

• At speeds up to 50 km/h, the HDC status indicator lamp lights continuously if a valid gear is selected.
• At speeds between 50 and 80 km/h, the HDC indicator lamp flashes and on vehicles with a "high series" instrument cluster, a message is displayed in the message center notifying that the speed is too high. If the HDC switch is pressed when the vehicle speed is greater than 80 km/h, the HDC status indicator lamp will not light and HDC will not be selected.
• If the speed reaches 80 km/h or more, a warning chime sounds, the HDC function turns off, the status indicator lamp goes out and, on vehicles with a "high series" instrument cluster, a message is displayed in the message center notifying that the HDC system is off.

For more information, please refer to the chapter:

• Instrument cluster (413-01 Instrument cluster, Description and operating principle)
• Information and Message Center (413-08 Information and Message Center, Description and Operating Principle)

When the HDC system is activated, the ABS module calculates the set speed and compares it with the actual vehicle speed. The ABS module then activates the HCU in active braking mode if necessary to achieve and maintain the set speed. The operation of the vehicle's brake lights during HDC operation is controlled by the CJB.

Activating the brake pedal during active braking may result in a pulsation felt through the brake pedal.

The set speed varies between a minimum and maximum value for each gear and transmission range, depending on the driver's commands via the pedals: If the pedals are not used, the ABS module assumes a default speed value:

HDC Speed Setpoints

Set speed	Automatic transmission gear		Gearbox in a manual transmission
	1st and D	Reverse	1st	Reverse
By default	10 km/h	3.5 km/h	10 km/h	8 km/h
Minimum	6 km/h	3.5 km/h	7.5 km/h	8 km/h
Maximum	20 km/h	3.5 km/h	20 km/h	8 km/h

The set speed is varied between the minimum and maximum values using the accelerator pedal or by pressing the cruise control '+' and '-' buttons (depending on vehicle specification). The HDC set speed will also vary depending on the Terrain Response™ mode selected.

When the set speed changes, the ABS module limits the vehicle's deceleration and acceleration to -0.5 m/s² (-1.64 ft/s²) and up to +0.5 m/s² (+1.64 ft/s²) respectively.

To ensure a safe transition from active braking to releasing the brakes, the ABS module invokes a brake fade strategy that gradually reduces the braking force during active braking. The brake fade strategy operates if any of the following conditions are detected during active braking.

• HDC is disabled by using the HDC switch.
• Malfunction of a component used by HDC, but not critical to the brake reduction function.
• Pressing the accelerator pedal when the transmission is in neutral.
• Overheating of brakes.

If the brake fade is caused by HDC disengagement or component failure, the HDC function is cancelled by the ABS module. If the brake fade is caused by depressing the accelerator pedal while the transmission is in neutral or by brake overheating, the HDC function remains in a standby state and resumes operation when the accelerator pedal is released or the brakes cool.

The brake fade strategy increases the set speed with a constant acceleration of 0.5 m/s² (1.64 ft/s²) until the maximum set speed is reached or until active braking is requested for 0.5 seconds. If the accelerator pedal is positioned in the range that affects the set speed, the acceleration rate increases to 1.0 m/s² (3.3 ft/s²).

When a reduction in efficiency occurs, a warning chime sounds and the HDC status indicator lamp goes out. Then the HDC indicator lamp goes out (on the "low series" instrument cluster) or a message is displayed in the message center (on the "high series" instrument cluster) notifying of the malfunction.

For more information, please refer to the chapter:

• Instrument cluster (413-01 Instrument cluster, Description and operating principle)
• Information and Message Center (413-08 Information and Message Center, Description and Operating Principle)

When performance degradation occurs due to brake overheating, a message is displayed on vehicles with a "high series" instrument cluster notifying that HDC is temporarily unavailable. On vehicles with a "low series" instrument cluster, the HDC indicator lamp flashes. At the end of the performance degradation function, the HDC status indicator lamp flashes. The indicator lamps flash and/or the message continues to be displayed with HDC selected until the brakes have cooled.



For more information, please refer to the chapter:

• Instrument cluster (413-01 Instrument cluster, Description and operating principle)
• Information and Message Center (413-08 Information and Message Center, Description and Operating Principle)

To control brake overheating, the ABS module monitors the braking performance and estimates the temperature of each brake based on this. If the estimated temperature of any of the brakes exceeds a preset limit value, the ABS module initiates a brake reduction strategy. After a brake reduction cycle, HDC operation is enabled again when the ABS module estimates that the temperature in all brakes is less than 64% of the preset temperature limit value.

Maintaining stability while eliminating roll

The RSC function uses the brakes and engine to try to restore the vehicle's stability if the vehicle is involved in a sudden maneuver that threatens to cause the vehicle to roll over.

The ABS module monitors driver inputs and vehicle behavior using various powertrain signals and inputs from wheel speed sensors, steering angle sensor, roll, yaw, and lateral acceleration sensors. These inputs are compared with modeled behavior and, if the vehicle behavior reaches a predetermined risk level, the ABS module limits engine power or applies the brakes to one or more wheels to allow the vehicle to regain stability and assist the driver in controlling the vehicle.

When the ignition is on, the RSC function is always available, even if the DSC function is selected to be off.

Terrain Response™ System Integration

The Terrain Response™ function combines the ABS module and other vehicle control modules to facilitate vehicle movement off-road or in difficult road surface conditions. The Terrain Response system is activated when the rotary control switch is set to the special Terrain Response program.

When the Terrain Response special program is activated, the ABS module, along with other vehicle control modules, will operate according to programmed characteristic tables. The characteristic tables stored in the software allow the ABS system to operate according to a threshold value that will assist in the operation of the selected Terrain Response special program. For more information, refer to the chapter: Optimizing the vehicle's suspension and handling characteristics (204-06 Optimizing the vehicle's suspension and handling characteristics, Description and Operation).