Gearbox Interface (New Range Rover Only)

The gearbox interface to the GEMS ECM consists of 4 wires, three run directly to the gearbox via connectors C551 and C559. They consist of the throttle position, engine torque, ignition retard request, and a 4th wire which runs from the GEMS ECM to the gearbox ECM, via the BeCM and carries the engine speed signal.

When a gearbox fault occurs, you cannot extinguish the MIL until the gearbox is diagnosed, the fault rectified and cleared. Only when this is done can you go back to the GEMS diagnostics and clear the transmission "P" code that caused the MIL.

Keep the following in mind when attempting to diagnose gearbox problems:

^ If torque reduction faults occur, carefully check the wiring and connector integrity between the GEMS ECM and the gearbox ECM.

^ If throttle angle faults occur, do not assume the throttle potentiometer to be at fault. It can be caused by an open circuit or high resistance in C551/C559. Check the throttle readings within the gearbox diagnostic and GEMS diagnostic to confirm it is working OK. The GEMS ECM will flag a fault if the throttle pot is truly faulty.

^ If engine speed faults occur, check the crank sensor for security. Especially pre SA316306 vehicle (see Crank Sensor section). Check the wiring and connector integrity from the GEMS ECM to the BeCM to the gearbox ECMs. The gearbox ECM is very sensitive to engine speed abnormalities, especially during cranking, and can occasionally pick up an abnormality the GEMS ECM would not detect.

^ The tachometer on the instrument pack is very sensitive to engine speed abnormalities and can sometimes be seen to drop suddenly in synch with an engine speed miss.
This can be useful in trying to identify if an engine speed signal fault is present. A possible cause can be the shield wire shorting out to the speed input at the harness clamp by the battery box.

^ TextBook appears to lock up while trying to clear the gearbox fault It has not locked up, but refuses to accept any input from the main screen. A way to overcome this is to select the screen wipe feature. Touch the upper left corner of the screen and confirm the screen wipe action. TextBook will now accept the fault clear command.