VANOS is a system that varies the timing of the valves by moving the position of the camshafts thus allowing the timing between intake and exhaust valves to be changed.
At lower engine speeds, the position of the camshaft is moved so the valves are opened later, as this improves idling quality and smooth power development. As the engine speed increases, the valves are opened earlier: this enhances torque, reduces fuel consumption and lowers emissions. At high engine speeds, the valves are opened later again, because this allows full power delivery.
Single VANOS – The first-generation single VANOS system adjusts the timing of the intake camshaft in discrete steps (eg the camshaft is advanced/retarded at certain engine speeds. VANOS was first introduced in 1993 on the BMW M50 engine used in the 5 Series.
Double VANOS – The second-generation double VANOS system adjusts the timing of the intake and exhaust camshafts with continuously variable adjustment, based on engine speed and throttle opening. The first double VANOS system appeared on the S50B32 engine in 1996.
There are only a couple of scanners available that can properly access and test that system. Here are a couple of examples of actual vanos tests using the factory ISTA/D. Note the difference in test procedures between early and later vehicle, early using tests procedures found in DIS.
2000 E39 M5
Customer’s complaint; rattles at startup and sometimes at idle
Results; camshaft sensor was bad. Customer was quoted by two other shops for full vanos unit replacement when it fact it was a sensor.
2008 E92 335i
Customer’s complaint; check engine light on
NOTE: ISTA/D recognizes that the misfires are secondary faults
Results; Unfortunately for this vehicle it has the dreaded “dig of the plain compression ring into the bearing bank”
The digs of the plain compression ring into the bearing bank can occur on both the intake side (N53 and N54 engines) and on the exhaust side (all NG6 engines). The front section and rear section of the bearing bank can also be affected.