High engine speed

At high engine speed, the rocker arm oil control solenoid is turned on by the ECM/PCM. Oil pressure from the rocker arm control solenoid enters into the intake primary rocker arm via the rocker shaft, and it moves the VTEC switching piston in the rocker arm. This causes the VTEC switching piston to slide into the intake secondary rocker arm, locking the rocker arms together. Both intake rocker arms are lifted by the high lift cam lobe.

Fig 1: VTEC Operation Diagram (High Engine Speed)

Courtesy of AMERICAN HONDA MOTOR CO., INC.