Automatic Transmission Diagnosis - With Codes: Operation: Diagnostics: Notes

If there is a fault, the automatic transmission will attempt to drive as normally as possible. However, if it is not safe to continue changing gears, a limp home mode will be selected.

Limp home mode differs depending upon the vehicle conditions when the fault is diagnosed. If high range is selected, the transmission will default to 3rd gear (if vehicle is stationary) and 4th gear (if vehicle moving). If low range is selected, then the system will attempt to maintain the current gear until the ignition supply is removed. This is in case the fault occurs while negotiating a steep gradient.

If there is a fault which either prevents all gears being used or disables the kick-down facility, the sport and manual lights will flash at the same time. This indicates to the driver that the vehicle has entered limp home mode. This mode will continue until the ignition is turned off. When the ignition is turned back on and the engine has been cranked, the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) will complete a self-test. If the fault has rectified itself the automatic transmission will resume normal operation and the sport and manual lights will no longer flash. If a fault has been rectified or is no longer present but the fault code has not been deleted, the sport and manual lights will continue to flash until the EAT ECU has diagnosed the fault is no longer present.

If any of the above conditions are true, the software within the transmission EAT ECU will have stored a fault code. After a fault code has been stored and the vehicle has completed 40 warm-up cycles, the vehicle fault code will be deleted from memory providing the fault does not reappear during this time. A warm-up cycle is completed when a running engines coolant temperature rising by at least 61 F° (16 C°) and exceeding 158 F° (70 C°). If the fault codes reappear, this counter is reset and requires another 40 warm-ups before the fault is deleted automatically.

If the automatic transmission EAT ECU is found to have been disconnected, the vehicle will have selected an hydraulic limp home mode. Reconnection must occur when the ignition is switched off. If the EAT ECU was disconnected while the ignition was turned on, fault codes will have been stored within the ECM and EAT ECU. These fault codes must be deleted using Land Rover TestBook/T4 scan tool or other suitable scan tools.

While the ignition is on, the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) diagnoses the system for faults. The extent of the diagnostic capability at any particular time depends on the prevailing operating conditions (e.g. it is not possible to check torque converter lock-up while the vehicle is stationary, or to check for a short circuit to ground if the circuit concerned is already at a low potential).

If a fault is detected, the EAT ECU immediately stores a fault code and the values of 3 operating parameters associated with the fault. Depending on the fault, there are 4 possible effects:

• The fault has little effect on automatic transmission operation or vehicle emissions. The driver will probably not notice any change and the warning lamps remain extinguished.
• The fault has little effect on automatic transmission operation but may effect vehicle emissions (e.g. torque converter not functioning or 3rd/ 4th gear permanently selected) and if the fault is detected on a second consecutive drive cycle, the MIL illuminates.
• All gears are available but kickdown does not function. The sport and manual warning lamps flash. The MIL remains extinguished.
• Limp home mode is selected and vehicle performance is greatly reduced. The sport and manual warning lamps flash and if the fault is detected on a second consecutive drive cycle, the MIL illuminates.

After the detection of a fault, the effects remain active for the remainder of the drive cycle. In subsequent drive cycles, as soon as the EAT ECU diagnoses the fault is no longer present, it resumes normal control of the automatic transmission. The conditions required to diagnose that the fault is no longer present depend on the fault. Some faults require the engine to be started, others require only that the ignition is switched on.

Only 5 different faults can be stored in the memory at any one time. If a further fault occurs, the fault with the lowest priority will be replaced by the new fault.