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The VVT system controls intake camshaft valve timing to provide improved engine performance, fuel economy, and reduced exhaust emissions. VVT system consists of camshaft timing OCV for VVL system may also be referred to as camshaft timing oil control valve VVL or Variable Valve Lift VVL oil control valve Toyota Sequoia 2001 Repair" href="/sequoia-2001-repair/note-ocv-for-vvl-system-may-also-be-referred-to-as-camshaft-timing-oil-control-valve-vvl-or-variable-valve-lift-vvl-oil-control-valve.html">oil control valve, variable valve timing controller on intake camshaft, crankshaft position sensor, Engine Control Module (ECM), camshaft position sensor and associated wiring. See Fig. 73 -Fig. 75 .

NOTE: Camshaft timing oil control valve may also be referred to as oil control valve for VVT, VVT Oil Control Valve (OCV) or camshaft timing oil control valve VVT. vvt-controller.html">Variable valve timing controller may also be referred to as variable valve timing actuator or VVT controller.

Intake and exhaust camshaft are driven by a timing chain and drive gear on each camshaft. Intake camshaft drive gear is integrated with the variable valve timing controller to vary intake camshaft valve timing. Variable valve timing controller consists of a housing which is driven from the timing chain and a vane that is fixed on the intake camshaft. See Fig. 76 . Oil pressure may be delivered from advance or retard side of intake camshaft to the variable valve timing controller. This oil pressure causes variable valve timing controller to rotate, causing intake camshaft to rotate and change the valve timing. When engine is stopped, to improve stability,

2001 ENGINE PERFORMANCE Theory & Operation intake camshaft remains in the most retarded state. When no oil pressure is applied to variable valve timing controller immediately after engine is started, lock pin prevents movement of variable valve timing controller to prevent a knocking noise. Once engine is started and oil pressure exists at variable valve timing controller, the lock pin is released by the oil pressure.

Camshaft timing oil control valve is an electrically controlled valve that receives oil pressure from the oil pump. See Fig. 72 . The ECM uses input signals for engine speed, intake air volume, throttle position and engine coolant temperature to determine operation of camshaft timing oil control valve. The ECM also uses input signals from camshaft position sensor and crankshaft position sensor for determining the actual intake camshaft valve timing. Camshaft position sensor may also be referred to as variable valve timing sensor. The ECM operates camshaft timing oil control valve by controlling position of spool valve. This determines which side of variable valve timing controller the oil pressure will be applied to for advancing or retarding the valve timing by rotating the intake camshaft. See Fig. 72 . When engine is stopped, camshaft timing oil control valve is in the retarded state.

When engine is idling, intake camshaft valve timing remains at the standard or hold position to stabilize the idle and obtain better fuel economy. During light engine load, intake camshaft valve timing remains retarded to provide stable engine operation. During medium engine load, intake camshaft valve timing is advanced to provide increased performance, fuel economy and improved emission control. During heavy engine load in low-to-medium-speed range, intake camshaft valve timing is advanced to provide increased torque. During heavy engine load in high-speed range, intake camshaft valve timing is retarded to provide improved high-speed range operation and better fuel economy. During cold temperatures, intake camshaft valve timing is set at the standard or hold position to stabilize fast idle speed and obtain better fuel economy. When engine is started or stopped, intake camshaft valve timing is remains at retarded position to improve engine starting.

If a problem exists in the VVT system, a Diagnostic Trouble Code (DTC) may be stored in ECM. See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article for retrieving of DTCs.

2001 ENGINE PERFORMANCE Theory & Operation

Fig. 73: Identifying Variable Valve Timing System Components (Celica, Corolla & MR2) Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

Fig. 73: Identifying Variable Valve Timing System Components (Celica, Corolla & MR2) Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

2001 ENGINE PERFORMANCE Theory & Operation

Fig. 74: Identifying Variable Valve Timing System Components (ECHO & Prius) Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

Fig. 74: Identifying Variable Valve Timing System Components (ECHO & Prius) Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

2001 ENGINE PERFORMANCE Theory & Operation

Fig. 75: Identifying Variable Valve Timing System Components (Highlander 2.4L 4-Cyl. & RAV4) Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

2001 ENGINE PERFORMANCE Theory & Operation

Fig. 76: Identifying Variable Valve Timing Controller Components (Celica, Corolla, ECHO, Highlander

Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

Fig. 76: Identifying Variable Valve Timing Controller Components (Celica, Corolla, ECHO, Highlander

Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.

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