Es300 & RX300
VVT system controls intake camshaft valve timing to provide improved torque, improved fuel economy and reduced exhaust emissions. VVT system consists of 2 oil control valves, 2 VVT controllers, crankshaft position sensor, oil pump, Engine Control Module (ECM) and associated wiring. See Fig 1.
Exhaust camshaft is driven by timing belt, and intake camshaft is driven by a gear on end of exhaust camshaft. Intake camshaft drive gear is integrated with VVT controller to vary intake camshaft valve timing. VVT controller consists of a housing driven from exhaust camshaft and a vane that is attached to intake camshaft. See Fig 2. Oil pressure sent from advance or retard side path at intake camshaft causes rotation in VVT controller resulting in a change in valve timing.
Oil control valve is an electrically controlled valve that receives oil pressure from oil pump. See Fig 3. ECM uses input signals for engine speed, intake air volume, throttle position and engine coolant temperature to determine operation of oil control valve. ECM also uses input signals from VVT sensors and crankshaft position sensor for determining actual intake camshaft valve timing. ECM operates oil control valve by controlling position of spool valve in oil control valve. Positioning of spool valve determines which side of piston oil pressure will be applied on. By applying oil pressure on piston, piston will move inward or outward, causing intake camshaft valve timing to change.
During light load, intake camshaft valve timing is retarded to provide stable engine operation. During medium load, intake camshaft valve timing is advanced to provide increased fuel economy and improved emission control. During heavy load in low to medium speed range, intake camshaft valve timing is advanced to provide increased torque. During heavy load in high speed range, intake camshaft valve timing is retarded to provide improved high speed range operation.
If a problem exists in VVT system, a Diagnostic Trouble Code (DTC) may be stored in ECM. DTC may be retrieved from ECM for system diagnosis using a scan tool. See appropriate SELF-DIAGNOSTICS article.