Land Rover Discovery: Transmission Fault Status

If the TCM detects a fault with the transmission system, it will enter a default (limp home) mode to prevent further damage to the transmission and allow the vehicle to be driven. If possible reverse gear will be available and also 3rd gear only.

When a fault is detected, a high speed CAN powertrain systems bus message is sent from the TCM and is received by the instrument cluster. The instrument cluster illuminates the MIL (if required) and displays an applicable message in the message center.

For additional information, refer to: Instrument Cluster (413-01 Instrument Cluster, Description and Operation).

Some transmission faults may not illuminate the MIL or display a fault message, but the driver may notice a reduction in shift quality.

TOUCHPOINT ADAPTIONS

The transmission is supplied by ZF with Touchpoint Adaptions set in the Transmission Control Module (TCM) at the factory which match the transmission to which the TCM is attached.

CAUTION:

TOUCHPOINT ADAPTIONS MUST ONLY BE PERFORMED WHEN A NEW TCM OR A TCM FROM ANOTHER VEHICLE HAS BEEN FITTED. UNDER NO OTHER CIRCUMSTANCES MUST TOUCHPOINT ADAPTIONS BE PERFORMED. Resetting Touchpoint Adaptions for any reason other than replacing the TCM could result in poor shift performance if the procedure is carried out unnecessarily.

Before performing a diagnostic Touchpoint Adaption reset procedure using an approved Land Rover diagnostic system, ensure the following conditions are applied:

• the Automatic Transmission Fluid (ATF) is at a temperature greater than 30 degrees C (86 degrees F)
• the Transmission Control switch (TCS) is in the 'Park' position
• the vehicle is stationary
• the engine is running at idle speed
• Brake pressure applied using the foot brake
• the Electric Parking Brake (EPB) is applied and held on manually to ensure it does not release when 'Drive' is selected
• no faults or Diagnostic Trouble Codes (DTCs) are present in the TCM.

NOTE:

If the EPB is allowed to release, the Touchpoint Adaption reset procedure will be terminated.

When the transmission is built, it is tested at the ZF factory to determine how much electrical current is required by each Pressure Control Valve (PCV) to attain a datum engagement point. The engagement (Touchpoint) is determine by a predefined level of friction in the clutch plates.

This data is stored with the serial number of the transmission and the same data is written to the TCM fitted to that transmission. This ensures that each transmission has a uniform performance.

If the Touchpoint Adaption data is not available because the TCM or the transmission has been replaced, the Touchpoint Adaptions contained in the TCM will be incorrect for the transmission. This will result in harsh clutch engagements and could cause damage to the transmission.

Using the Touchpoint Adaptions learning routine in the approved Land Rover diagnostic system, enables the TCM to establish the Touchpoint for all the clutches. Once the Touchpoint Adaptions have been learnt, the Clutch Adaptions routine must be performed to further refine the transmission operation.

CLUTCH ADAPTIONS

When the vehicle is driven, the TCM monitors and refines the clutch pressures and engagement points to maintain smooth transition between gear changes.

After certain service operations, the Clutch Adaptions may need to be reset to restore optimum performance of the transmission.

When the vehicle is driven, the TCM monitors the gear changes. When the TCM determines that smooth and reliable changes are occurring, it initiates a Clutch Adaptions learning cycle. The learning cycle determines if higher or lower PCV pressures are required or if PCV timing can be improved to apply smoother gear change transitions. The dynamic behaviour of each clutch is monitored and can be compensated for. The TCM will also monitor static engagement when the vehicle is stationary.

The Clutch Adaptions are initially started after a reset with drive cycles including the ability to cruise at various speeds. The fully Clutch Adaptions are achieved gradually over many drive cycles.

The Clutch Adaptions ensure that the transmission provides smooth gear changes without slip for the life of the transmission. The Clutch Adaptions compensate for wear providing that the Touch Adaptions were correct for the static calibration of the transmission.

The Clutch Adaption process compensates for assembly build tolerances in the hydraulic system, mechanical tolerances of the transmission components to include friction and electrical tolerances for example resistance and inductance. All of these can affect the dynamic behaviour of the transmission.

The Clutch Adaptions ensure that the TCM is operating at its optimum operating parameters adjusted to suit the individual characteristics of the transmission. The TCM to a lesser extent, also adjusts to the characteristics of the driver and vehicle.

NOTE:

Some drivers and their driving style may inhibit the Clutch Adaption process, which can lead to transmission driveability issues over a period of time.

Instrument ClusterEngine Speed and Torque Monitoring

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