What Is Variable Valve Timing (VVT)

How does VVT work?

There are several systems and methods used to achieve VVT. Modern VVT systems are computer controlled and utilize electrical solenoids to control valve timing change. When the solenoids are energized, they act upon the components used in the system for making the mechanical timing adjustment. This is commonly done hydraulically with the use of pressurized engine oil, although some systems vary in design.

What vehicles have VVT systems?

VVT systems have become extremely common, almost all vehicles today come equipped with some form of variable valve timing system.

Do I need to maintain my VVT system?

While most VVT system components are maintenance free. The VVT system is greatly affected by engine oil condition and viscosity. For your VVT system to operate properly, you must service your engine oil regularly following the manufactures recommended intervals.

VVT failures

The most common failure points of VVT systems are:

• Engine oil issues, such as low level, poor condition, or incorrect viscosity
• VVT solenoid failure
• Circuit/Wiring problems Many VVT related trouble codes are due to mechanical problems caused by lack of maintenance, such as stretched timing chains and clogged oil passages.

What happens when a VVT system Fails?

The level of concern regarding the failure of a VVT system depends on the type and severity of the failure. While a failed VVT solenoid might cause poor engine performance and the check engine light to illuminate, it can also fail due to low engine oil or low engine oil pressure, which may lead to severe engine damage.

VVT system components

• VVT solenoid: The electrical component energized by the engine control module to adjust the valve timing. Most VVT solenoids are used to divert pressurized engine oil to camshaft actuators or phasers
• Camshaft actuator/phaser: The camshaft actuator, or cam-phaser is the mechanical device that physically adjusts the valve timing. There are several different designs, but they are commonly controlled by high pressure engine oil that is routed from the VVT solenoid
• Oil control valve/spool valve: A mechanical valve used to control the flow of engine oil to different passages for VVT control. This device is normally part of the VVT solenoid on overhead cam engines
• VVT oil pressure switch: A normally open switch that closes from oil pressure when the VVT system is activated. It is used on some vehicles to confirm VVT operation.
• Engine oil passages: Passages throughout the engine block, cylinder heads and camshaft that allows engine oil to flow to VVT system components.
• Camshaft and Crankshaft position sensors: Used by the engine control module to monitor and control valve timing location. It is common for multiple camshaft position sensors to be used on VVT systems that phase multiple camshafts.
• Engine control module: The module responsible for monitoring and controlling the VVT system as well as the engine

VVT system not activated

Most VVT systems are not activated at idle and start adjusting valve timing at higher engine speeds. When the VVT system is not activated the engine runs in its default or base timing position. In the default position the VVT solenoids are not energized, and the actuators are commonly locked into their home position by a locking pin or spring. Pressurized engine oil is still being supplied to the oil control valves but it is bypassed and directed back into the oil pan. In this state the engine control module monitors the system and waits for the engine speed and load conditions to be right for VVT activation.

VVT system activation

When the engine control module activates the VVT system it starts by energizing the VVT solenoid. Depending on the system the solenoid can be commanded on/off or energized on a duty cycle, or a pulse, that is based on the amount of adjustment desired. In most systems, the VVT solenoid moves the oil control valve to direct pressurized engine oil to the actuator or phaser. Once the oil control valve allows pressurized engine oil to flow to the actuator, the actuator adjusts the valve timing to the desired position. The engine control module monitors the camshaft and crankshaft position sensors to confirm the adjustment and to precisely monitor the timing of the engine. If a fault is detected the system usually defaults to base timing and a diagnostic trouble code is set.