VVT: Variable Valve Timing

By the early 1990s, almost all automotive manufacturers had a successful variable valve timing (VVT) system in production. VVT systems offer higher performance at higher RPM.

VVT Operation

VVT Engine Cross section
VVT systems are simple to diagnose.  Most parts are non-serviceable and have integrated sensors.  On a conventional engine, exhaust and intake valves are open or closed depending on the crankshaft and the pattern cannot be altered.  With VVT, it is possible to have the timing altered to match the engine speed, torque requirements, and valve overlap.   This increases both performance and fuel economy.  Another great advantage of VVT is its ability to take some of the load off the crankshaft by opening the valve before the end of the combustion stroke.Cam Shaft Moving Pistons  VVT systems have made Exhaust Gas Recirculation (EGR) valves obsolete.  EGR valves put smog causing nitrous oxides back into the intake manifold.  The VVT system controls the timing to leave inert gas in the chamber for the next combustion cycle, thus controlling the combustion temperature and the production of nitrous oxides.

VVT Diagnosis

Cam Shaft and Chain
Two common error codes technicians run across with VVT systems are P0011 and P0021 (Camshaft position sensor “Bank 1” and Camshaft position sensor “Bank 2,” respectively).  These codes (like any code) don’t entirely mean the sensor is faulty, so look at the VVT system for a fault and check the sensor as well.  Some of the common areas to look into are: valve timing, oil control valve, oil control valve filter screen, camshaft timing/gears, and the electrical side of the operation as well as the PCM.  First thing to do is to check the oil because dirty oil can lead to sludge buildup which can damage the oil passages in the cam resulting in cam failure.  Lack of regular maintenance is a big problem with VVT systems.

In the future, VVT systems will be quite commonplace, because of the performance and emissions benefits they have.