Variable Valve Timing (VVT) system — description
1. The VVT system varies intake and exhaust camshaft timing by directing oil pressure to advance or retard the camshaft sprocket/actuator assemblies. Changing the camshaft timing during certain engine conditions increases engine power output, fuel economy and reduces emissions.
2. System components include the Powertrain Control Module (PCM), the VVT oil control valves (OCV) and the intake and exhaust camshaft sprocket/actuator assemblies (see illustration).
i. 2 The Variable Valve Timing (VVT) oil control valves located in the valve cover
1. Intake camshaft VVT oil control valve
2. Exhaust camshaft VVT oil control valve
3. The PCM uses inputs from the following sensors to turn the oil control valve on or off:
- Vehicle Speed Sensor (VSS)
- Throttle Position Sensor (TPS)
- Mass Airflow (MAF) sensor
- Engine Coolant Temperature (ECT) sensor
4. Once the VVT oil control valves are actuated by the PCM, they direct the specified amount of oil pressure from the engine to advance or retard the camshaft sprocket/ actuator assemblies (see illustration).
i. 4 Locations of the intake (A) and exhaust (B) camshaft actuators
5. The camshaft sprocket/actuator assembly is equipped with an inner hub that is attached to the camshaft. The inner hub consists of a series of fixed vanes that use oil pressure as a wedge against the vanes to rotate the camshaft. The higher the oil pressure (or flow) the more the actuator assembly will rotate, thereby advancing or retarding the camshaft.
6. When oil is applied to the advance or retard side of the vanes, the actuator can advance or retard the camshaft timing. The PCM can also send a signal to the oil control valve to stop oil flow to both (advance and retard) passages to hold camshaft(s) in its current position.
7. For camshaft sprocket/actuator removal and installation, see Timing chain and sprockets — removal, inspection and installation. For VVT oil control valve removal and installation, see Emissions and engine control systems.