Variable Valve Timing (VVT)

A fixed camshaft is a compromise between low-speed torque and high-speed power. VVT lets the control unit advance or retard the camshaft as conditions change. Makers use different names, such as VANOS, VTC or VVT-i. Most systems use an oil-pressure phaser on the camshaft controlled by a solenoid valve. Clean oil at the right level and grade is essential.

Manufacturers use different names, such as VANOS, VVT-i or VTEC. Some systems change only timing, others also change valve lift, and a few can vary both continuously. Engines with variable valve timing on both intake and exhaust camshafts can reduce or even replace an EGR valve, because overlapping the valve openings keeps some exhaust gas in the cylinder.

The control unit sets a target cam angle and pulses the oil control valve. The camshaft sensor reports the actual angle, and the control unit corrects the difference. Most systems use an oil-controlled actuator (cam phaser) at the end of the camshaft, controlled by a solenoid valve.

Low or dirty oil, a sticking oil control valve or a stretched chain cause codes such as P0011 or P0014, rough idle and rattling at start-up. Low oil, the wrong oil grade or sludge can disturb the system and set codes such as P0010 to P0025. Regular oil changes are key.