Rough run. VANOS.

This theme applies not only to engines of series N43/N53, but also other petrol engines of BMW, which are equipped with VANOS.

This topic was actualized, thanks to my friend Rob.

He took the restoration of his car’s engine very seriously. In the beginning, the performance of NOx system was restored, using NOXEM; new adaptations were created; software release for MSD80 was updated to newest version available. After each of operations, the performance of engine was improving, but some unevenness was still observed.

Needless to say, that no error messages in MSD80 memory could be found regarding this, misfire counters of cylinders were close to 0.


The mystery was solved, when after some time the engine switched to emergency mode and the following error message was recorded:


2A99 crank shaft – outlet camshaft, correlation


After replacing the VANOS valve for exhaust, the performance of engine became normal, and no more unevenness was observed.

This case prompted me to study hidden causes of defects of VANOS. The key word is “hidden”, because the regular defects (sensor, solenoid, mechanical problem) would be recognized by self-diagnostics system. The repair is of VANOS is simple, spare parts – easy accessible.


Information regarding basic performance principles of VANOS is quite accessible, for example:

Despite the fact, that the structure of VANOS is very simple – it’s management contains only solenoid, which is managed by DME, and camshaft sensor (which identifies real position of camshaft), this knot has certain nuances, which has to be taken in account.

VANOS has no separate (it’s own) position sensors, which would immediately inform the DME regarding acquired position of camshaft.  The position is controlled according to data of turnarounds of current camshaft gearwheel. Unfortunately, the impulse frequency even by 2000 .. 4000 RPM is only several tenths of Hz, what means that the information regarding position of camshaft is restored relatively rarely. That, in turn, means, that short-term inadequacy between inquired and confirmed position is possible. It is not “visible” to DME and, even if the DME “see’s” it, it can not eliminate it completely (for example, if the VANOS mechanism has reacted to pulling, or, for example, temporarily stucks). If we talk scientific terms – the time of data updating is close to time of system’s  reaction – this is not a good practice.


For example, the error message:

2A99 crank shaft – outlet camshaft, correlation

means: data, received from camshaft sensor (signal amplitude, shape of the signal, frequency) are within the limits of norm; the calculated position of camshaft changes (the mechanism is not mechanically jammed), but the difference of inquired and confirmed position has been over the norm for a longest while.

Manufacturer, as usually, don’t gives any information regarding conditions, when this error message is recorded, so we had to do some research – is the inadequacy of inquired and confirmed position “visible” by using diagnostic tools, for example, INPA. The situation is even more complicated by the fact that restoring of INPA live data is performed only several times during one second – if it’s a short-term problem, it can be skipped.


From several suspicious vehicles with this possible problem was chosen one with N53B30  engine. NOx system works correctly; no error messages in MSD memory; misfire counters of cylinders are close to 0. One and only suspicious mode: 110 .. 130 km/h, when the desulphurising of NOx catalytic converter is in progress. In this mode the engine performs quite uneven. The unevenness is much “softer” than in case with misfires, but still – it can be felt.

Inspection of live data with INPA in idle shows correct data in all menus, including VANOS. For example, VANOS shows a little increased offset type adaptation of exhaust camshaft (around 4 .. 5 degrees), but inquired and confirmed positions for both camshafts corresponds and are very stable.


The content of VANOS menu.

(1) offset type adaptation of the intake camshaft

(2) offset type adaptation of the exhaust camshaft

(3) confirmed position of the intake camshaft

(4) confirmed position of the exhaust camshaft

(5) inquired position of the intake camshaft

(6) inquired position of the exhaust camshaft


Check-up of the live data with INPA, VANOS menu:

  • In the beginning of video: the engine runs idle; as can be seen, inquired and confirmed positions corresponds precisely, confirmed positions – very stable;
  • In the middle part of video: the accelerator pedal is being pressed fast. As can be seen, confirmed positions of both camshafts confirm the inquired ones. VANOS works – no doubt about it;
  • In the end of video: around 3000 RPM is kept. As can be seen, confirmed position of exhaust camshaft look’s quite suspicious – it doesn’t stay’s still “on place”, but changes values all the time. Inquired value is 115,4 degrees, but confirmed positions is 113,1 .. 118,4 degrees; it means that the confirmed position fluctuates for 5,3 degrees.

Checking live data with INPA in these current problematic driving conditions (speed 110 .. 130 km/h, desulphurising of NOx catalytic converter) shows:

  • in both banks, Lambda is maintained correctly, integrators are changing in range of several %;
  • misfire counters are 0, for all cylinders;
  • according to air mass-meter data, the amount of air used changes in range +/- 10 .. 15%;
  • the pressure of high pressure pump doesn’t changes, also inquired torque (the problem is while using cruise control, on even road) and RPM of engine don’t changes.

The last two conditions are very interesting, seemingly incompatible things.


Menu of VANOS positions in these current conditions:

As we can see in this video:

  • the confirmed position of intake camshaft is stable and corresponds to inquired one;
  • the inquired position of exhaust camshaft is unchanged: 120,2 degrees, confirmed one changes in range from 115,2 to 123,6 degrees, it means, the confirmed position fluctuates in range (at least) of 8,4 degrees!

The precision of crankshaft position displaying is 0,3 .. 0,4 degrees (can be seen by fluctuation of intake camshaft data fluctuation): the position of intake camshaft changes in range +/- 1 “step”. But the position of exhaust camshaft changes even in range of +/- 10 “steps”, it is maintained less precisely for around 10 times!

Clear conclusion – the exhaust camshaft VANOS knot has problems! Additionally – as there are performance conditions, when the defect is not observed (confirmed position is maintained stable), it is obvious, that the problem is caused by solenoid, not by increased angular play in VANOS rings or shaft drive.

The problem with camshaft position explains also seemingly incompatible things – changing air consumption and unchanging fuel mixtures composition in unchanged engine load and RPM. When the phase of camshaft changes, the “breathing” of engine changes – the fulfilling of cylinders changes, also the gas outlet of combustion chamber changes. Accordingly – the air depression (short-time) in the inlet manifold and the amount of counted air.


Needless to say, that BMW dealer will not see such problem, because:

  • the dealer is not allowed to officially use the INPA;
  • the dealer will not perform (in regular case) the test drive with customer’s vehicle (and live data analysis one time), to look for hidden defects;
  • renewal time of ISTA D data on screen subjectively is even more slower, no visual interpretation of data is available (as bars), displayed data are in very small size and are not easy to see – this defect is simply not noticeable with ISTA.

Part number of solenoid for N53 series engine: 11367585425

Notice: both intake and exhaust camshafts have identical solenoids; the same ones are used also in engines of N52 series.

Part 2.

In this video you can evaluate accuracy of confirmed position of exhaust VANOS at 2000 .. 3000 RPM (at neutral) after solenoid replacement:

and accuracy of confirmed position at different driving conditions (60 .. 120 km/h):

As you can see, ‘jittering’ has fallen down to +/- 1 ‘step’, uneveness – dissapeared.


It is very convenient to observe the performance of VANOS also in test block of VANOS. MSD80 loader 2.023 offers also the possibility to observe PWM values, supplied to VANOS ../F6/F2/F2.
In idle, PWM for both VANOS valves is 10% – valves are deactivated.

In range above 1000 RPM, the valves start to maintain required position.

Correct PWM values of valves in even performance mode (for example: 90 .. 100km/h, 5/6th gear): 30 .. 50%. Acceptable short-term fluctuation of PWM values (with stable/invariable required position): +/-2 .. 3%.

If in the same moment, when the required position of VANOS changes (the engine performance mode changes), PWM of the valve for a short moment rapidly drops to 10% or rapidly grows to 90% – VANOS (in this moment) has problems to maintain the required position of the camshaft.
If increased jittering of PWM of the valves is observed, and if it regularly reaches 10/90% – VANOS knot has problems with maintaining of required position, and it could be the cause of uneven engine performance (even if there are no error messages regarding VANOS performance).


Related entries:

Oil supply. N series engines

MSD80 diagnostics

Cold engine and problems of injectors

N53. Problem of cylinder No3

N43 and strange behavior