VANOS timing trouble: DTC P0011/P0012 on the BMW N52

Your BMW is usually smooth and responsive from low rpm. Lately it feels sluggish pulling away from a stop, the idle hunts a little while the engine is still cold, and the check engine light comes on. The scan result shows P0011, or P0012.

Both codes are related to VANOS, BMW's camshaft timing control system. Many owners jump straight to a failed timing chain, when the more common cause is much simpler and cheaper. On the N52 engine, there is a sensible order of checks to separate oil problems, solenoid problems, and mechanical problems. This article discusses what the codes mean, how VANOS works on the N52, and the inspection steps.

P0011 is the generic OBD-II code "A Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)": the position of camshaft A (on most engines, the intake camshaft) on bank 1 is too far advanced from what was requested, or the system performance is not as expected. P0012 is its pair, "A Camshaft Position - Timing Over-Retarded (Bank 1)": the same camshaft lags behind the requested timing.

The engine computer compares the commanded camshaft position with the actual position from the camshaft sensor and the crankshaft sensor. If the difference is too large or lasts too long, the code is stored. This code does not point to one component. The cause can be low or dirty engine oil, an oil viscosity that does not fit, a stuck control solenoid, the camshaft actuator, or a worn timing chain.

The N52 is an inline six-cylinder gasoline engine that replaced the M54, first used in the E9x 3 Series and E6x 5 Series. It came in 2.5 and 3.0 L versions and was used in, among others, the E90 325i and the E60 525i. Its engine block uses a magnesium-aluminium alloy, and its valve system combines Valvetronic (valve lift control) with double VANOS.

Double VANOS means the timing of the intake camshaft and the exhaust camshaft are adjusted separately. The adjustment uses engine oil pressure directed by an electronic solenoid to an actuator at the front end of the camshaft. The engine computer reads the crankshaft and camshaft sensors, then commands the solenoid to open the oil path to advance or retard the camshaft. So VANOS depends heavily on three things: a solenoid that works well, enough oil pressure, and a timing chain that is not slack. Variants and model names differ by market, so confirm that your car's engine code is really N52.

Because VANOS is driven by oil, the condition of the engine oil directly affects the camshaft's ability to move as commanded. Oil that is low, used for too long, dirty with deposits, or with a viscosity that does not meet the manufacturer specification can make the actuator slow to move and trigger P0011 or P0012. Varnish and debris from the oil can also clog the VANOS solenoid.

That is why VANOS diagnosis on the N52 should start with the simplest step: check the engine oil level with the correct procedure, look at the oil change history, and make sure the oil used meets the BMW specification for that engine. If the oil is indeed overdue or does not fit, change it first, clear the code, then watch whether the code returns before taking other components apart.

On a double VANOS engine like the N52, one simple test is often used to confirm a bad solenoid: swapping the position of the intake solenoid with the exhaust solenoid. After swapping, the code is cleared and the car is driven. If the fault follows the solenoid to the exhaust side, that solenoid is the problem. If the code stays on the intake side, the cause is probably elsewhere, for example the actuator, oil pressure, or timing chain.

Before or after the swap test, the solenoid can be checked: its coil resistance is measured according to the BMW specification, and the solenoid is checked for varnish or debris. If a new solenoid has been installed and the code quickly returns, the next step is the camshaft actuator, then the timing chain on an engine that shows signs of a slack chain.

• Engine oil that is low, dirty, used too long, or with an unsuitable viscosity.
• A timing control solenoid (on a BMW, the VANOS solenoid) that is stuck, dirty, or electrically faulty.
• A camshaft actuator (phaser) that is stuck or worn.
• A worn or slack timing chain, so the camshaft position shifts.
• A camshaft or crankshaft sensor, or its wiring, giving a wrong signal.

1. Read all codes and note the conditions when the code appeared. Misfire codes or sensor codes that are also stored can change the starting point.
2. Check the engine oil: level, age, and whether it meets the BMW specification. Change it if in doubt, then clear the code and watch.
3. Look at the requested and actual camshaft position data with a diagnostic tool that can read the BMW engine module.
4. Do the VANOS solenoid swap test for intake and exhaust, and check the solenoid's resistance and cleanliness.
5. Check the oil pressure if the solenoid proves good.
6. Only then check the actuator and timing chain. A slack chain can produce symptoms similar to VANOS failure, so do not replace VANOS components if the chain has not been checked.

With P0011 or P0012, the car can generally still be used carefully for short distances, but its power can drop and incorrect timing can damage the engine if it is ignored. Schedule an inspection as soon as possible, and in the meantime avoid high rpm and heavy loads. If the engine oil turns out to be low, topping it up to specification is a safe first step before the car is taken to a workshop.

Stop using it if the engine runs very rough, stalls by itself, makes a rattling sound, or the oil pressure light comes on. In that condition, pull over in a safe place, turn off the engine, and check the oil level before deciding the next step.