The Cavalier/Calibra 4x4 system uses hydraulic oil pressure, from the power steering system, to operate the transfer box. The application of the required pressure is controlled electrically by the 4x4 ECU. A safety system is also incorporated to disengage the transfer box when the brakes are applied over 25 km/h (16 MPH).
As part of the hydraulic cycle for the power steering, a small quantity of oil, under pressure, is bled via a regulator valve to supply and charge the accumulator. Because it is bled by the regulator valve, a constant pressure is maintained in the accumulator, without impairing the operation of the power steering system.
Fluid pressure is supplied, via a solenoid operated control valve, to operate the transfer box pressure plate, or ram, and thus operate the multi-plate clutch to deliver 4WD.