Intake valve side

At low engine speed, the rocker arm oil control solenoid (rocker arm oil control solenoid A) is turned off by the ECM/PCM. Oil pressure from the rocker arm oil control valve does not enter the intake rocker shaft. Each intake rocker arm is separated by a return spring and lifted by each low lift cam lobe.

Fig 1: Identifying Intake Valve Side In VTEC System Operation

Courtesy of AMERICAN HONDA MOTOR CO., INC.

At high engine speed, the rocker arm oil control solenoid (rocker arm oil control solenoid A) is turned on by the ECM/PCM. Oil pressure from the rocker arm control solenoid enters the primary intake rocker arm via the intake rocker shaft, and it moves the VTEC switching piston in the rocker arm.

This causes the VTEC switching piston to slide into the intake mid rocker arm and the intake secondary rocker arm, locking the rocker arms together. Both intake rocket arms are lifted by the high lift cam lobe.

Fig 2: Identifying High Lift Cam Lobe In VTEC System Operation

Courtesy of AMERICAN HONDA MOTOR CO., INC.