The Vanos Solenoid Valve (SOLV) is a critical part of the variable camshaft timing in modern BMW's. A common fault component on all N55 & S55 engine models, these valves have a tendency to go bad and can cause a wide array of problems, from erratic engine performance, warning messages to hard starting and a rough idle. Engine problems can come and go as these valves start to go bad but, with being such an important but sensitive component, a quality replacement is a must.