BMW E90 N52 vanos solenoids and timing fault P0012
What causes fault code P0012 in the N52 engine?
P0012 means the camshaft timing is too retarded. The cause is often contamination in the vanos oil passages: clogged screens and check valves prevent control pressure from reaching the solenoids. A centre bolt left out when changing the oil filter can also cause jerking and a warning light.
Which vanos parts should you replace first?
The intake and exhaust side vanos solenoids are the same part (11367585425), and they are easy to replace. The vanos filter, or check valve (11367541692), is on the side of the cylinder head, and two are needed. The screens can be removed by lifting the car and taking off the front wheel. The camshaft position sensor can also be replaced directly.
What to do if replacing the solenoids does not fix the fault?
Replacing the solenoids does not necessarily remove the fault completely. Next, check the camshaft position sensor, the cam gears (adjusters), the camshaft pressure seals and cylinder head wear. With the INPA or ISTA diagnostic programs you can see whether the fault is on the intake or exhaust side, and run a vanos test with them.