During 3 Cylinder Mode

When rocker arm oil control solenoid A (Bank 1) is turned on by the PCM, the rear rocker arm oil control valve switches the oil pressure. Oil pressure then enters the rear bank cylinder's primary rocker arms from the oil passage in the rocker shaft, causing the VTEC switching piston to slide into the secondary rocker arms and against the return spring. This disengages the primary rocker arm from the secondary rocker arm to stop valve activation. The rear bank cylinder's rocker arms do not move, and rear bank cylinders are paused. At the front bank, oil pressure from the front rocker arm oil control valve locks the No. 4 cylinder's primary and secondary rocker arms together. The No. 4 cylinder's rocker arms are moved by the camshaft, and all front bank cylinders are active.

Fig 1: VCM System-Operation Diagram - 3 Cylinder Mode (Rear Bank 1 And Front Bank 2)

Courtesy of AMERICAN HONDA MOTOR CO., INC.