Variable Valve Timing (VVT) System

The VVT system controls intake camshaft valve timing to provide improved torque, improved fuel economy and reduce exhaust emissions. VVT system consists of oil control valve, intake camshaft sprocket, crankshaft position sensor, camshaft position sensor, VVT sensor (GS400, LS400 and SC400), oil pump and Engine Control Module (ECM).

Intake camshaft sprocket consists of an outer gear that is driven by the timing belt, inner gear that attaches to intake camshaft and a piston that moves between inner and outer gears. When the piston moves, the helical splines on the piston causes the inner and outer gear positions to change, resulting in a change in valve timing.

NOTE: Intake camshaft sprocket may also be referred to as VVT controller. Oil control valve may also be referred to as OCV or camshaft timing oil control valve.

Piston movement is determined by the oil control valve. The oil control valve is an electrically controlled valve that receives oil pressure from the oil pump. The ECM uses input signals for engine speed, intake air volume, throttle position and engine coolant temperature to determine the operation of the oil control valve. ECM also uses input signals from camshaft position sensor, VVT sensor (GS400, LS400 and SC400) and crankshaft position sensor for determining the actual intake camshaft valve timing. The ECM operates the oil control valve by controlling position of spool valve in the oil control valve. Positioning of spool valve determines which side of the piston the oil pressure will be applied on. By applying oil pressure on the piston, the piston will move inward or outward, causing the intake camshaft valve timing to change.

When the engine is started or shut off, the oil control valve is positioned so intake camshaft valve timing is retarded. When engine is idling or during low load, intake camshaft valve timing is retarded to provide stable engine operation. During medium load, intake camshaft valve timing is advanced. During high load in low to medium speed range, intake camshaft valve timing is advanced to provide increased torque. During high load in high speed range, intake camshaft valve timing is retarded to provide improved high speed range operation. During cold temperature operation, intake camshaft valve timing is retarded to provide stable idle and increased fuel economy due to the lower fast idle speed.

If a problem exists in the VVT system, a Diagnostic Trouble Code (DTC) may be stored in the ECM. DTC may be retrieved from ECM for system diagnosis by using a scan tool. See SELF-DIAGNOSTIC SYSTEM .

NOTE: Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the Engine Control Module (ECM). The second category covers OUTPUT SIGNALS, which are components controlled by the ECM.