System Description: VTEC: Notes

This system improves fuel efficiency and reduces exhaust emissions at all levels of engine speed, vehicle speed, and engine load.
The VTEC system changes the cam profile to correspond to engine speed. It maximizes torque at low engine speed and output at high engine speed.
The low lift cam is used at low engine speeds, and the high lift cam is used at high engine speeds.
The rocker arm oil control solenoid switches both intake rocker arms of the VTEC system on and off; the solenoid is controlled by the ECM/PCM.
The rocker arm oil pressure switch detects VTEC system oil pressure and sends this information to the ECM/PCM.

ROCKER ARM OIL PRESSURE SWITCH POSITION TABLE

ENGINE SPEED	ROCKER ARM OIL CONTROL SOLENOID	ROCKER ARM OIL PRESSURE SWITCH	INTAKE VALVE LIFT
LOW	OFF	ON	LOW
HIGH	ON	OFF	HIGH

Fig 1: Identifying VTEC System Components With Valve Timing Graph

Courtesy of AMERICAN HONDA MOTOR CO., INC.