Interface to Auto Gear Box Control Unit (Z255)

Gear position Switch-pins 14, 33, 50, Diesel (pins 36, 8, 37 Petrol)
The Gear Box Position Switch (X294) is mounted on the side of the gearbox and contains 3 internal switches which are connected to the Auto Gear Box Control Unit (Z255) via pins 50,14 and 33 for Diesel (pins 36, 8, 37 for Petrol). By analyzing the status of these 3 switches, the Auto Gear Box Control Unit (Z255) calculates which gear the vehicle is in.

If a fault occurs with the switch, then the Auto Gear Box Control Unit (Z255) may try to put the gearbox into a different gear than the driver's request.

Solenoid Valves-pins 5,6,19,24,42 Diesel (pins 5, 30, 32, 33, 53 Petrol)
The Auto Gear Box Control Unit (Z255) has control over 4 solenoid valves: MV1, MV2, torque converter lock up and pressure regulator. These are all supplied via pin 19 Diesel (pin 53 Petrol), which is activated via a relay in the Auto Gear Box Control Unit (Z255) itself.

MV1 - pin 5 Diesel (pin 30 Petrol), MV2 - pin 24 Diesel (pin 33 Petrol)
When the driver selects "D"rive, then the Auto Gear Box Control Unit (Z255) controls the gear selection by the use of the two solenoid valves. If a fault occurs with one or both of the valves, then a different gear than the one selected will result. If the Auto Gear Box Control Unit (Z255) defaults the gearbox, then the common supply to all the solenoid valves is removed and the gearbox mechanically shifts either to third gear, if the vehicle is stationary, or fourth, if moving.

MV2 is also used to prevent the driver from selecting reverse when the vehicle is moving forward at more than 8 km/h and from disengaging reverse at reverse speeds greater than 6 km/h. This is known as "Reverse Safety" and will not be available if MV2 is non-operational and/or the gearbox has defaulted.

Torque Converter Lock-Up Solenoid - pin 42 Diesel (pin 32 Petrol)

The torque converter slips to allow smooth operation of the gearbox. Lock-Up occurs when the vehicle reaches a speed of 45 mph or above in either third or fourth gears.

Pressure Regulator Solenoid - pin 6 Diesel (pin 5 Petrol)
The gear shift quality is controlled by modulating the pressure regulator, which is controlled by the Auto Gear Box Control Unit (Z255). The solenoid is energized closed, such that if a failure occurs, then the regulator allows default gear change.

Output Shaft Speed Sensor -pins 2, 38, 20 Diesel (pins 42,14,15 Petrol)
The automatic gearbox system incorporates an output shaft speed sensor which is input to the Auto Gear Box Control Unit (Z255) on pin 2 Diesel (pin 42 Petrol) and pin 38 Diesel (pin 14 Petrol) with a screen over the cable attached to pin 20 Diesel (pin 15 Petrol). It is important that this signal is screened correctly.

MES 1 and 2-pins 16, 31 Diesel (pins 25, 51 Petrol)
The two Manual/Economy/Sport (MES) lines indicate to the BeCM (Z238) which mode has been selected or if a fault within the transmission has occurred.