A variable valve timing (VVT) solenoid is a device that controls oil flow to the VVT actuator to help adjust engine timing across a range of engine performance needs.
Engine function requires that a small army of moving parts - from four to eight pistons, a crankshaft, camshafts, and as many as thirty two valves, along with dozens of other components - all march together at the same time. Like instruments in an orchestra, all of these components must be synchronized. In an engine with traditional fixed timing, the relationship between moving pieces remains the same no matter what performance is called for.
With variable valve timing, the engine timing can be adjusted on the fly to accommodate low, mid, and upper-range performance. In the process, it helps to improve efficiency, horsepower, and emissions. The VVT solenoid changes the amount of oil pressure sent to the VVT actuator to allow the timing of the camshaft(s) to be advanced or retarded.
In contrast to other engine timing services, replacement of a variable valve timing solenoid does not typically require significant disassembly of engine components. Rather, the solenoid is accessible from outside the engine.
In general, a technician might have to set aside some components for access, engine shields, wires, and the like. But removal of the old VVT solenoid requires only that one to three bolts be extracted and an electrical plug be disconnected. Care must be taken to ensure that the new part is properly seated and sealed to prevent oil leaks.