Interface to Auto Gear Box Control Unit (Z255)

GEAR POSITION SWITCH-PINS 14, 33, 50
The gear position switch is mounted on the side of the gearbox and contains five internal switches, although only 3 are connected to the Auto Gear Box Control Unit (Z255) via pins 50, 14, and 33. By analysing 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
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, which is activated via a relay in the Auto Gear Box Control Unit (Z255) itself.

MV1 - pin 5, MV2 - pin 24:
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:
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:
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 energised closed, such that if a failure occurs, then the regulator allows default gear change.