Variable Camshaft Timing (VCT) Unit Schematic - Retard

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

To retard the camshaft timing, the PCM adjusts the signal to the VCT solenoid to move the spool valve to close the retard chamber oil passage and connect the advance chamber oil passage to the inlet oil.

Each momentary decrease of the torque acting on the camshaft causes oil to transfer from the advance chamber, through the spool valve and the retard check valve to the retard chamber, and so retard the camshaft timing.