How the Terrain Response system works (Discovery 3)

When the system is running "Terrain Response" the following vehicle subsystem control units are used:

• Engine management system (engine control module)
• Gearbox control system (transmission control module - only for vehicles with automatic transmission)
• Transfer case control system (transfer Case Control Module)
• Rear Differential Control System (rear Differential Control Module - if equipped)
• Air suspension control system (air suspension control unit)
• Brake system (aBS/DSC/ETC/HDC functions) (aBS module).

Each subsystem operates differently depending on the selected system program. "Terrain Response", providing optimum traction, stability and control of the vehicle when driving on a certain terrain. The system has a "safety margin" that guarantees the safe use of any program on any surface, even if an inappropriate program is selected.

Engine Management System (EMS)

The engine management system changes the throttle response to accelerator pedal movement and thereby regulates engine torque. The engine management system can select one of the throttle control programs, which provide for different torque changes for the same pedal stroke. The engine management system can also change the throttle response to regulate the permissible torque change depending on pedal stroke.



Each program of the system "Terrain Response" sets a specific combination of operating parameters for all subsystems. Switching between programs causes a different set of operating parameters to be selected, which is felt by the driver. The driver notices a difference in the response of the engine and throttle. For example, if the accelerator pedal is held in one position and the program "Grass/Gravel/Snow" is switched to the "Sand" program, the torque and engine speed increase. When switching from the "Sand" program to the "Grass/Gravel/Snow" program, the driver will notice a decrease in torque and engine speed.

NOTE: The change in torque and speed occurs within approximately 30 seconds. Do not accept the system program changeover. "Terrain Response" for a malfunction of the engine management system.

Automatic transmission control system

The transmission control module changes the gear shift pattern according to the selected program. "Terrain Response". This change results in earlier or later upshifts and downshifts.

When starting off on a slippery surface, the 2nd gear of the highest stage or the 3rd gear of the lowest stage will be engaged to prevent wheel spin. When driving on mud, the gearbox will provide maximum torque. When driving on sand, the gearbox will ensure maximum use of engine power.

When using the special program "Slow movement on rocky terrain", first gear will be engaged for starting off.

Sport mode is only available when the general program and the highest gear of the transfer case are selected. Sport mode does not work in the lowest gear and when any special program of the system is selected. "Terrain Response". CommandShift™ mode is available in any program selection in both high and low gears.



If the transmission is in sport mode and a special program is selected, the transmission will automatically switch to manual mode. "CommandShift™". If a special program is already selected and the gear selector lever is moved from the 'D' position to the 'Sport' position, the transmission will automatically switch to 'CommandShift™' mode.

Transfer case and rear differential control system

Electronically controlled transfer case differential and electronically controlled rear differential (if available) are considered as a single system. An electronically controlled rear differential is optional on vehicles equipped with the system. "Terrain Response". There are two differential control strategies: active and reactive.

An active strategy is to predict the locking torque required by each differential to minimize slip and ensure maximum stability. Each program "Terrain Response" has different threshold values and criteria for the active strategy. The active strategy improves the traction and stability of the wheels by preventing wheel slip. This is achieved by predicting the required locking torque for the selected program. For example, a higher locking torque is required for driving on rocky or slippery terrain.

When using the reactive strategy, the torque required for locking varies depending on the actual wheel slip and the vehicle's driving dynamics. Each program "Terrain Response" correspond to certain threshold values and input data for the reactive strategy. The reactive strategy improves the traction of the wheels and the stability of the vehicle by eliminating the wheel slip that remains after the application of the active strategy.



The torque applied for locking depends on the selected program. "Terrain Response". For example, on a slippery road, the least amount of torque is required to ensure maximum traction and minimum damage to the surface.

To calculate the locking torque, various signals from other subsystems are used, such as engine torque, throttle position, gear selection, steering wheel angle, vehicle speed, lateral acceleration, and yaw rate.

The ABS dynamic stabilization function has priority over the differential control system "Terrain Response" and may cause a reduction in locking torque during its operation. For more information, refer to Anti-Lock Control - Traction Control (206-09A Anti-Lock Control - Traction Control).

Air suspension control system

The air suspension control unit provides automatic switching between normal and off-road height. Information about the height change is provided via the instrument cluster message center and LED symbols on the switch. Automatic height adjustment of the vehicle suspension provides an increase or decrease in ground clearance, which allows you to make the most of the selected program "Terrain Response".

With a correctly fitted Land Rover approved towbar, when an electric load is connected to the towbar, the suspension height cannot be changed. A message will appear in the message centre to inform you that a trailer is connected and the off-road height cannot be selected automatically. The driver can raise the suspension manually using the air suspension switch.

NOTE: The automatic height change lock only operates if the vehicle is fitted with a Land Rover approved towbar and an electrical load is detected at the towbar socket.

Anti-lock braking system

The ABS module controls several vehicle functions and adjusts the operating parameters of these functions to optimize the selected program. "Terrain Response".

The traction control system uses different slip/acceleration thresholds to improve traction and vehicle stability. For example, the sensitivity of the system increases when driving on slippery roads to reduce wheel slip.

If using a special program "Terrain Response" the dynamic stabilization function is turned off (using the DSC switch on the instrument panel), when you subsequently select another program, the dynamic stabilization system is automatically switched on again.

The Dynamic Stability Control uses different thresholds for the selected program to reduce its impact and eliminate the need for the driver to switch off the Dynamic Stability Control to reduce engine intervention, which is sometimes required in severe off-road conditions. When driving in deep sand, in addition to selecting the Sand program, it may be useful to switch off the Dynamic Stability Control function using the DSC switch on the instrument panel.

The controlled descent system switches on and off automatically and the set speed is set according to the selected program. "Terrain Response". The sensitivity of the controlled descent function can also be increased if necessary.



The controlled descent function is switched on and off at optimal times. The set speeds of the controlled descent system are also adjusted depending on the operating conditions of the vehicle.

Incorrect use of programs

The driver is informed about the incorrect selection of the program in the following ways:

• The symbol for the selected program flashes continuously on the instrument cluster message centre display.
• System control unit "Terrain Response" blocks certain functions of some programs, e.g.: the cruise control function is only available when special programs or the "Grass/Gravel/Snow" program is switched off.; the transmission's sport mode is switched off when using any special program.
  • the cruise control function is only available when the special programs or the "Grass/Gravel/Snow" program is switched off.;
  • the transmission's sport mode is switched off when using any special program.
• If any special program other than the Grass/Gravel/Snow program is selected and the ignition is switched off for more than 6 hours, the system "Terrain Response" disables all special programs by default.
• If the Grass/Gravel/Snow program is selected, the system "Terrain Response" never defaults to the default mode or turns off this special program. This feature is intended for use in cold climates where the Grass/Gravel/Snow program must be used at all times.
• The "Rocky Climb" program is only available in the lowest gear of the transfer case.

Selecting a program that is not appropriate to the road conditions does not pose a danger to the driver or the vehicle. Continuous use of an inappropriate program may shorten the service life of some components. The driver may notice a decrease in the vehicle's dynamic performance due to a deterioration in the engine and gearbox response compared to the mode in which special programs are turned off. In addition, in some programs, the controlled descent function remains on, as indicated by the HDC indicator on the instrument panel. Also, when driving in some special programs, the driver may notice that the center and rear differentials are locked, causing "slowing down".



System control unit "Terrain Response" controls the use of special programs of the system, recording the mileage and time of operation of the car under the special program at the highest and lowest levels. This information can be read using T4 and then used to analyze customer complaints. For example, high fuel consumption can be associated with the constant use of a special program.

Information for the driver

For all cars with the system "Terrain Response" a high-level instrument panel is installed, which has a message center for displaying various information. The message center display contains program symbols "Terrain Response", which display the selected program. If the symbols are not displayed, it means that the special program is not selected and the system is operating in the mode without special programs.

The driver is also informed of any necessary changes in the status of the subsystems via indicators on the instrument panel or corresponding messages on the message center display, for example, the system informs about the controlled descent function being switched off or the air suspension height being changed.

Under certain conditions, the system "Terrain Response" it can also display tips or warnings to help the driver get the most out of the vehicle, such as:

• The message center display shows the steering wheel angle, which helps avoid driving in deep ruts with the steering locked.
• Displays the recommended gear when driving on slippery roads
• If the system automatically sets the ride height for off-road driving and the driver then lowers the suspension to normal height, the system can warn the driver that the vehicle may bottom out.

The messages displayed in the instrument cluster message center display are discussed in detail in the Information and Message Center section. For additional information, refer to Information and Message Center (413-08).