Transfer box interlock (where fitted)

The transfer box interlock is controlled by the IDM to prevent transfer box shifter operation unless certain preconditions have been satisfied.

The transfer box interlock prevents the transfer box being shifted from High or Low to neutral with the ignition key removed from the ignition switch. When the BCU senses that the ignition key is removed from the ignition switch, it signals the IDM via the serial data bus. The IDM then provides an earth path for the coil of the transfer box relay, energizing the relay coil and closing the relay contacts to provide a voltage supply to the transfer box interlock solenoid.

A diode is included in the supply line to the solenoid to prevent residual current causing the solenoid to stick in the energized position.

The transfer box solenoid interlock option can be programmed in one of three states dependent on market/ customer requirements, these are:

• Option 1- not fitted.
• Option 2 - normal operation.
• Option 3 - inhibit transfer box.

The BCU checks the status of the following inputs to determine the logic action for employing the transfer box interlock solenoid (transfer box solenoid enable):

• Ignition state.
• Gearbox state.

In the event of a communications link failure occurring while the transfer box enable is on, the output will be switched off.