This unique type of oil consumption has led to premature failure of parts like spark plugs, catalytic converters, engine mounts, pistons/rings, and cylinder walls. When VCM disengages, the engine then misfires if needing to clear the cylinder of oil. However, the reciprocating effect of the piston with closed valves reportedly produces a vacuum condition where oil can get pulled past the piston rings to flood the cylinder. In theory, the closing of all rear bank valves produces an ‘air spring’ effect. A single solenoid on the rear camshaft is activated to close oil pressure to unlock the cam followers, thereby closing the valves. The VCM hydraulic circuit control is defaulted open, meaning that the engine has to build up enough oil pressure on initial startup to disable the rear bank of cylinders. When the VCM system disables cylinders, an "ECO" indicator lights on the dashboard, Active Noise Cancellation (ANC) pumps an opposite-phase sound through the audio speakers to reduce cabin noise, and Active Control Engine Mount (ACM) systems reduce vibration. The engine's drive by wire throttle allows the engine management computer to smooth out the engine's power delivery, making the system nearly imperceptible on some vehicles. The system operates through controlling the flow of hydraulic engine oil pressure to locking mechanisms in the cam followers. A solenoid unlocks the cam followers on one bank from their respective rockers, so the cam follower floats freely while the valve springs keep the valves closed. Unlike the pushrod systems used by DaimlerChrysler's Multi-Displacement System and General Motors' Active Fuel Management, Honda's VCM uses overhead cams. The most recent version of VCM (VCM-3) reverted to the previous 3- and 6-cylinder operation. The second version of VCM (VCM-2) took this a step further, allowing the engine to go from 6 cylinders, down to 4, and further down to 3 as the computer sees fit. Variable Cylinder Management ( VCM) is Honda's term for its variable displacement technology, which saves fuel by using the i-VTEC system to disable one bank of cylinders during specific driving conditions-for example, highway driving. Often referred to as the worst Honda innovation.
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