Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
GS300 & Is300
The VVT system controls intake camshaft valve timing to provide improved torque, improved fuel economy and reduced exhaust emissions. VVT system consists of an oil control valve, intake camshaft timing sprocket, crankshaft position sensor, camshaft position sensor, oil pump, Engine Control Module (ECM) and associated wiring. See Fig 1.
Intake camshaft timing sprocket consists of an outer gear that is driven by timing belt, inner gear that attaches to intake camshaft and a piston that moves between inner and outer gears. When piston moves, helical splines on piston cause inner and outer gear positions to change, resulting in a change in valve timing.
Piston movement is determined by oil control valve. Oil control valve is an electrically controlled valve that receives oil pressure from oil pump. See Figure. 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 camshaft position sensor 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.
When engine is started or shut off, oil control valve is positioned so intake camshaft valve timing is retarded. When engine is idling or during light load, intake camshaft valve timing is retarded to provide stable engine operation. During medium load, intake camshaft valve timing is advanced. 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. During cold temperature operation, intake camshaft valve timing is retarded to provide stable idle and increased fuel economy due to lower fast idle speed.
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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.