The Variable Cylinder Management (VCM) system is used only on 2006 and later 2WD models. Under certain conditions, such as light-load cruising and deceleration, the VCM system saves fuel by cutting the spark and fuel to the rear cylinders and deactivating the intake and exhaust valves. Because the valves are not being actuated, friction from valve spring compression is reduced. Piston drag is also reduced because no air is compressed as the pistons come up. To replace the Engine Oil Pressure (EDP) sensor, remove the engine cover, disconnect the EDP sensor electrical connector, unscrew the sensor from the rocker arm oil control solenoid valve, remove and discard the old EOP sensor O-ring. Installation is the reverse of removal. Be sure to use a new O-ring and tighten the EOP sensor. The rocker arm oil control solenoid valve is located on the left end of the rear cylinder head. To replace it, remove the engine cover, disconnect the EOP sensor electrical connector, remove the rocker arm oil control solenoid mounting bolts and remove the rocker arm oil control solenoid valve, remove the rocker arm oil control solenoid valve O-ring and filter. Inspect the filter for clogging. If it's clogged, replace the filter/O-ring, and replace the engine oil and the oil filter. Installation is the reverse of removal. Be sure to tighten the mounting bolts.