Land Rover Discovery Owners & Service Manuals

Land Rover Discovery: Engine Speed and Torque Monitoring

The ECM constantly supplies the TCM with information on engine speed and torque through messages on the CAN powertrain systems bus. The TCM uses this information to calculate the correct and appropriate timing of shift changes.

If the messages are not received from the ECM, the TCM will implement a back-up strategy to protect the transmission from damage and allow the vehicle to be driven.

In the event of an engine speed or torque signal failure, the transmission will adopt the electrical limp home mode with the transmission operating in a fixed gear.



Ensure that the remote handset remains in the vehicle whilst the vehicle is being recovered. Removing the remote handset will engage the steering lock, which will prevent the vehicle from steering correctly.

If the engine cannot be run whilst the vehicle is being recovered, there will be no power assistance for the steering or brakes. This will result in greater effort being required to steer or slow the vehicle.


The vehicle should not be towed more than required to load to a trailer or recovery vehicle.


  • The recommended recovery method is by trailer or recovery vehicle.
  • Where recovery to a vehicle or trailer is not possible (for example vehicle is off-road), the vehicle can be towed with all 4 wheels on the ground for a distance of up to 10 km (6.2 miles) at a speed no greater than 25 Km/h (15 mph). The Service Park Release (SPR) procedure must be used to disengage the park lock.

Secure the towing attachment from the recovery vehicle to the front towing eye.

Ensure the remote handset is in the vehicle and switch on the ignition (power mode 6) by pressing the start/stop button once.


Leaving the ignition switched on for extended periods will cause the battery to drain.

The Service Park Release (SPR) procedure must be used to disengage the park lock.

Release the electric park brake.

Tow the vehicle onto the trailer or recovery vehicle.

Apply the electric park brake and manually disengage the SPR, remove the pin and ensure the park lock lever is in the correct position to engage the park lock.

Switch off the ignition (power mode 4) and remove the remote handset from the vehicle.


The vehicle cannot be towed in a reverse direction.


Operation of the transmission is controlled by the TCM, which electrically activates various solenoids to control the transmission gear selection. The sequence of solenoid activation is based on programmed information in the TCM memory and physical transmission operating conditions such as vehicle speed, throttle position, engine load and rotary TCS position.

Engine torque is transferred, via operation of combinations of clutches to the planetary gear trains. The gear trains are controlled by reactionary inputs from brakes and clutches to produce the 9 forward gears and 1 reverse gear.

The shift elements (clutches and brakes) are actuated hydraulically. Fluid pressure is applied to the required clutch and/or brake, pressing the plates together and allowing drive to be transmitted through the plates. The purpose of the shift elements is to perform power-on shifts with no interruption to traction and smooth transition between gear ratios.



A = Hardwired; AN = High speed CAN Powertrain systems


  1. Transmission Control Module (TCM)
  2. Central Junction Box (CJB)
  3. Transmission Control Switch (TCS)
  4. Engine Control module (ECM)
  5. Anti-lock Brake System (ABS) control module
  6. Instrument cluster
  7. Valve block
  8. Transmission Control Switch (TCS)
  9. Ground
  10. Fuse - ignition supply from ignition relay
  11. Ignition relay (CJB)
  12. Fuse - Permanent battery supply


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