2011 BMW 335i - P0012 Vanos Intake Over-Retarded

Question

My E90 335i just threw a 'Reduced Power' warning on the iDrive screen. I pulled the codes and got P0012 (A Camshaft Position Timing Over-Retarded Bank 1). The car idles very poorly, almost sounds like a tractor, and there's a noticeable lack of torque in the low RPM range.

I've stayed on top of 5k-mile oil changes using Liqui Moly 5W-40. I'm worried the VANOS bolts have backed out (I know there's a recall for that) or the actual VANOS gear is toasted. I removed the intake solenoid and it didn't look particularly dirty or sludged up. What's the next logical step before I tear the valve cover off?

FleetOwnerFiona · Accepted Answer

✅ Confirmed fix: The intake VANOS solenoid was failing electrically when it got hot, but the main issue was the small check valves located in the cylinder head behind the wheel well liner.

I replaced both VANOS solenoids with genuine BMW units and, more importantly, removed and cleaned the VANOS check valves (non-return valves). The intake side check valve was partially clogged with tiny debris, preventing holding pressure. After cleaning the valves and installing the new solenoids, the 2D5A/P0012 codes disappeared and the idle smoothed out perfectly.

DIY_Denise · Answer

If the code didn't move when you swapped solenoids, the problem is likely the oil filter housing bypass valve or the filter itself. If you use a cheap oil filter or the 'cage' inside the filter housing cap is missing, it won't build enough oil pressure to actuate the VANOS hubs properly.

2011 BMW 335i - P0012 Vanos Intake Over-Retarded

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