BMW VANOS Explained (No Magic Necessary)

In the good old days, engine tuning done by timing adjustments was easy enough.  The crankshaft drove the timing chain, which spun gears in the head and turned the cams.  It was popular (and still is) to put a different style of cam in to improve performance over a certain spectrum.  In those days you had to decide whether or not you wanted low end torque for cruising around town or high end power for performance and racing, both offering significant tradeoffs.  The timing and functional performance of the engine was fixed in place.

That is, until technology became more widely available that allowed the timing to change on the fly.  Many manufacturers came out with designs to allow Variable Valve Timing (VVT), all with different solutions to the same problem.  How can we achieve the flatest power curve possible on a non-turbo engine, while reducing emissions and fuel consumption?  The ability to change the timing of the engine on the fly is a wonderful, magical invention that allows an engine to perform well driving around town at low RPM, as well as at higher RPM when your right foot demands some oomf.  One of the more famous acronyms is Honda’s ‘VTEC’, which utilizes multiple cam profiles to not only change timing, but duration and lift. I won’t blow your mind today with the complexity of that system.  BMW’s Variable Valve Timing system is called VANOS (Variable Nockenwellen Steuerung), and here’s how it works!

The VANOS unit lifted off, notice how the cam and the cam gear are independent of each other without the VANOS gear in place.  Image courtesy of Beisan Systems.

This is the single VANOS engine (found in M50 engines). It controls the intake cam gear, which is mechanically linked to the exhaust gear with a chain.

The key of the VANOS design is that the cam gear and the cam itself are independent, and both have splines.  The gear/cup in the VANOS system inserts in between these two parts, mechanically linking them.  The VANOS gear has two sets of splines, the outer for the cam gear and the inner for the cam itself.  The splines have a twist to them, also known as a helical gear, so as the gear inserts itself further between the cam and cam gear, the relative position changes, if by only a few degrees.

At idle, the gear is retracted.  As the RPM bumps off idle, the cup inserts further into the gear and advances intake valve timing.  This creates intake and exhaust valve overlap, allowing for exhaust gas recirculation (an operation designed to improve emissions while cruising).  When accelerating into the higher RPM ranges, the solenoid closes and the cup retracts once again, reducing overlap and going for max power.  It should be noted that this solenoid gets a real workout, and is a common failure in these engines as they age.

The VANOS solenoid opens, allowing the helical gear cup to push forward and change the orientation of the cam in relation to the gear a number of degrees.

Double VANOS has a hydraulic pod (found in later cars) extending into both cam gears, and has control over both intake and exhaust cam timing independently.  This system is much more advanced than single VANOS, allowing for constantly variable timing.  The ECU can change the intake and exhaust cam timing, and however it so pleases.  Using different maps for different situations (IE warm up, cruising, thrashing).

In all practical senses, the system is quite simple and ingenious.  Many of the best car makers do it. All it takes is putting a few different shaped gears together to pull off something amazing.  Now in 2016, you will see that nearly all automakers have some form of variable valve timing, but BMW was one of the few early companies to take full advantage of such a system early on.

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30 thoughts on “BMW VANOS Explained (No Magic Necessary)
  1. marc wolfe

    I have a 2011 with 138k and am having this system replaced for the second time plus I had the factory recall. Any ideas on what gives? (535ix)

    • dom and geovanna tarabocchia @

      were having distorted messages about the vanos and eccentric valve sensor
      have to pay 2700 for labor and parts on engine
      kinda foolish
      its possible we might go after bmw
      would you also be interested
      maybe we could get other people with same problem
      2011 was last year for engine so it shoud been just about perfected
      there ad cost more to maintain coffee machine for 5 years than bmw
      how about after 5 years might cost more than any other car manufacturer
      this car is so complicated run flat tires, battery in trunk, chassis stabilization
      come on whats going on

      • YamiGirl

        I completely agree . I can go on and on about coils misfiring, engine running roughly, and I love my car (650i) triple black convertible…58k miles. It is a beautiful car, however too many computer glitches. All brand new spark plugs and coils. I have had the computer replaced twice (while still under warranty). Out of warranty thousands of dollars spent…I will never buy one again as much as I love it. After having a completed the cylinder engine re-do with sparks and coils, (computer fully regeristing) -I am not a fan any longer! I will go with Mercedes-Benz or possibly Honda now.

        • TommiGirl

          I agree with you YamiGirl. It’s my car a 2011 E90 3 series. Last year of the 3 series as inline 6 without turbo. shld have been perfected. Only 64K at this time (jan 2019) and the ESS and Valvetronic Motor (which is used now instead of the VVT ) and I can see it running over time into thousands of dollars. Just the high cost of repair and maintenance of a complex car. Had a saab and costs were pretty high too from the 8th year onwards but nothin like this. 14th year I think I had to spend about 3k repair from swedish imports and I turned it in at 110K miles.
          I love european cars and they do drive and feel different when driving it, but costs are high. On the other hand Hondas and Toyotas feel very “floaty” when i drove them and if I had to go would go the Subaru way or maybe the Honda Accord 2L engine turbo I4 in max 2 years from now.

  2. Greg Hanawalt

    Do you have to replace both Vanos and the solenoid at the same time.Or maybe just one vanos. Have 2006 300i sports package

    • Adam Goral

      Hey Greg, you can replace just the solenoid by itself, the Vanos should be fine unless some sort of mechanical damage occurred. The actual Vanos assembly is little more than a bracket and mechanical linkage to transmit the actions of the solenoid.

  3. Jakub kolaczynski

    If you have an m3 with a double vanos motor let’s say a 2011 do you still need to replace the sylenoid is it a common problem and do the valves still need to be adjusted every X miles? Thanks!

    • Adam Goral

      I’m not specifically aware of VANOS issues with the S65 engine, but it is also a fairly new design so we will see how they pan out. Regardless, VANOS failure is a result of a failed solenoid in most cases, no matter what the engine is.

  4. Marsil

    Great job guys, I would like to know what goes wrong in the solenoid and can I bench test them with 12v dc battery, realistically speaking it’s a plunger an electronic one there is no difference between an OEM or aftermarket one as long as the plunger opens and closes based on this explanation

  5. Tamara

    I have an 2008 X3 – manual shift and just love my car! My mechanic just called and said I may have a Vanos problem. My car has just about 200,000 of endlessly fun highway miles! I just can’t get my head around the fact he said I should trade it in. My husband says he can’t believe a BMW can’t get over 200,000. I purchased this car new and have treated it well! I pulled around a 1,900 lb. travel trailer one summer, but it is a “Sports Utility Vehicle” and it’s made for that, right!

    What to do? The mechanic said if I traded it in, I would get a great trade-in value for a new car, but then I asked, “wouldn’t this problem become someone elses”? He said my car would be sold for parts or someone would pick it up as a side project!

    Is it worth it to put about $5000 into my car to get it back on the road, and this doesn’t account for the approximated estimate of $9,000 to replace the VANO system?

    • Adam Goral

      It sounds to me like your mechanic is trying to take you for a ride, you should find another one and never go back there. There is no possible way that fixing an issue with the VANOS (a small device located right on the top of the engine) can cost upwards of $9,000. You could most likely completely replace the engine for that. Unless there are other major issues with the car that he didn’t mention, you should be able to keep driving this car for years to come with proper oil changes and regular maintenance.

      Go on google, or look on forums or BMW groups on social media for help or advice on finding a local BMW specialist. Even if you have a completely blown engine or transmission, you most likely can still repair your car for a fraction of that quoted price at a different independent shop that would rather keep your business. If you need a quote on parts let us know exactly which ones you need.

      Even if you need to replace the entire top of the engine due to some catastrophic failure, a knowledgeable independent should be able to utilize lower mile used parts that are in good condition to repair your X3.

  6. AHS

    Aloha, This thread is the closest that I have come to finding an the answer of how the VANOS works.
    My problem.
    I am trying to figure out just what effect the VANOS system has on a cold starting situation.
    The vehicle in question is a 99 323i.
    Being in Hawaii, it seldom gets below 60f. On mornings when the temp does dip below 55f, the engine has trouble turning over, and once started, runs rough for maybe 30 seconds when it smooth’s out.
    Doubt it is fuel related, unless it is starved for fuel. (no fuel smell, or black smoke on start up)
    The cranking part is what I am most concerned about. The starter acts as if the battery is low, only instead of a constant dragging, it engages, turns the engine maybe a half a turn, and then disengages. If the key is held in the start position, the starter will rapidly engage and disengage, while the dash lights and interior lights dim just as they would if the battery was low.
    Another symptom is the engine sounds as if it is cross firing… IE “kicking back” while trying to start.
    Other times it almost seems as if the engine is hydro locked, in that the starter engages, but the engine will not turnover.
    The engine has no problems starting when temps are above 60f, and once running after the cold start, it runs perfectly. Can turn it off right after it has smoothed out and it will restart normally.
    There are no strange noises from the engine, it has good power, fuel mileage is constant 21mpg during daily commuting.
    The vehicle has just over a 100k, and even though it was a one owner, there were no records with it, so I have no idea of what, if any maintenance has been done.
    Tests that I have preformed,
    leak down
    cooling system pressure
    fuel pressure
    all related power connections checked.

    Until I know just what role the VANOS has, if any during cold starts, I can not rule it out. I would think that such system would need oil pressure to function, and that the system would return to, if I may, the default, or off position if you will, when the engine is not running. And… the VANOS would have no effect on the engine valve timing until there was enough oil pressure to move the VANOS pistons, or am I totally mistaken about this theory of mine?
    My personal feeling is there are more than one faction going on here. IE, starter relay,(which I doubt, but still) a combination of bad ignition coils, CKP/CMP sensors, but I can not rule out the VANOS because I do not fully understand the function it has on a cold engine, if you can call an engine @ 55f cold. I can not imagine how hard it would be to start this engine @ or below freezing temperature’s.

    Codes have been a host of misfire related, which is to be expected, and one for the torque converter not seeing the correct temperature.
    Question is this, could the VANOS be the cause of this situation, and if so, why?

    Thanks in advance for any, and all advice.

    • Adam Goral

      If the car starts up and runs fine after the initial hiccup, I am leaning more towards air leaks in the intake and vacuum system causing this issue rather than the VANOS. There’s a common place in the intake elbow that gets a tear in it, which can cause some shuttering, particularly when cold. Another thing to look into is the condition of the DISA valve, which is placed in the intake and diverts air around to multiple intake runners. If it’s sticky or loose, you will have a rough start before it gets on its feet. It might not rattle, even if its a little sticky. There is an air seal that wears out there, which can shrink slightly when it’s chilly out. Also clean the idle air control valve, as well as the throttle body.

      The issue with starting might be unrelated, this is a tough one. It sounds like there may be an issue with the crank position sensor, which is highly effected by heat. However, without the go-ahead from the CPS, the starter will not engage so I’m a little stumped. Check the grounds on the starter as well to make sure you don’t have some corrosion or undervolts disengaging the starter solenoid prematurely. I’m wondering if the engine thinks it’s starting, disengages the solenoid, then for one reason or another it’s not enough to actually get it going.

      Is the battery in good shape? These cars are very sensitive to voltage. How do the spark plugs look? Have you ever done the ignition coils?

      • AHS

        Thank you for the quick reply. Yes this is quite an unusual situation, and I will check the items that you mentioned.
        At this point I am thinking that the rough running might be a result of the starter turning the engine a little and then not. If that makes any sense.
        The plugs did not look bad, but that is a matter of opinion. As stated, I have no history on this vehicle, so they could be OEM plugs, in which case they are due for a change.

        Although I have read several threads where people have had similar issues, and have replaced the plugs and the coils without seeing any changes… my thoughts are still with the coils and the plugs as a being at least part of the problem. I doubt that new plugs or new coils will have any effect on the starter issue, but it is worth a try. I still feel that there is more than one thing going on here.
        Another thought for the starting is a possible security system issue. But why only on the first start of the day?
        I’ll keep digging and report any definitive results.
        Again, thanks for the advice on this sticky situation.

  7. romain ULRICH

    hello, i have a bmw e39 528ia single vanos so i had a problem with the solenoid vanos that rolled my car very badly , and after changing the solenoid rolled weel for 4 days and then the same problem with the solenoid . could tell me why solenoid c is broken twice. thank you

  8. Abish Gopal

    Good day sir,

    Amazing post. I am a student and purchased an e36 325i ’93 model. I’ve done a complete overhaul on the engine. Car’s engine sounds lovely although everyone I start the vehicle the idle fluctuates for a while and then settles. The car’s extremely heavy on fuel and as a student that’s always been bad news. I just want to be able to sort that and then I can use it more often. The car might be low on power at low rpms as you mentioned above. What are the quick checks to know whether it’s the solenoid or the seals that causing this problem. Some recommend unplugging the vanos. And if I pay for a diagnostic to be done will this pick up as a failure.

    Please assist I’m sorry for the long message. I have never gotten the best experience yet in my 325i coupe 🙁

    Kind regards

  9. Philip

    Hi there,

    I think you’ve got the exhaust gas recirculation part for the single-vanos wrong. Valve overlap does not have this effect, but rather allows for a cleaner mixture in the mid-rpm range. The advanced timing of the intake valve allows the fresh air-fuel-mixture to be sucked in by the already leaving exhaust gases.

    Internal EGR only works with the exhaust valve being retarded, while the intake valve is also, which allows the exhaust gases to be sucked back into the cylinder on the induction stroke. This can’t be done in a single vanos layout.

    In addition to that the maximum power of the single vanos system in the high rpm range is not only rooted in the reduced valve overlap itself, but in the side effect of the intake valve being opened longer on the intake stroke and also a part of the compression stroke already. Although this seems illogical, the air is not pushed out the intake valve on the compression stroke. The air much rather compresses itself because of its own velocity, allowing more air to enter the combustion chamber. Just before this effect is reverted, the valve closes and therefore captures more air, than actually would fit into the cylinder.

  10. Marlon Ricardo Khan

    Hey fellow BMWers happy new year 2019,
    We have 2001 525I we are experiencing a trivial loss of power when the engine is started even when the car is on and hot the tachometer does not go higher than 1000 could this be a bad gas filter symptom or some other gas related issue? Also in my neck of the woods Trinidad we we have super unleaded gas and premium unleaded could this be an issue also?

    Thanks for your enthusiastic follow up will be appreciated

  11. lee

    I am looking for an answer to a puzzling issue. I have an 04 – 745li with 143K on it. Car cranks like a champ, rides like a champ but when under 3K rpm, it will stutter/jerk intermittedly. It’s not constant but, whether at 70 mph or 45 mph, I feel a jerk. The faster, higher rpm’s, the less stutter. This seems to occur more often when the terrain levels on the road change. If under load, climbing a hill or dip, no problem. But, when returning to level ground, it jerks, especially if cresting the dip or hill then, going downward. Or leaving a level road and going down a hill or dip, it stutters. I’ve had the transmission checked by a very reputable company. They found nothing wrong. Not throwing any codes at all. New plugs and coil pack. No change. Had it at a very reputable BMW shop. Couldn’t find anything wrong. Don’t think they drove it much. It seems to get about as bad as it gets when the engine is at full operating temps. Then there are days when it only does it may be once or twice in a 25 mile stretch. Was thinking it was a throttle body issue then, possibly a Vanos issue or possibly an electrical issue. It reminds me of water in the fuel or of an older Mercedes I had that a had a cracked insulator around a plug causing it to arc. Same stutter but, all that checked out fine. No blue lightening nor water in the fuel. Love my car but know this can’t be good for it. Any thoughts greatly appreciated.

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