I own a 2003 Mazda 6 with a 2.3L engine and automatic transmission. Recently, I've been receiving a P0012 'B' diagnostic trouble code. The engine is now exhibiting knocking or ticking noises and runs roughly, especially at idle. I've come across information about both P0012 'A' and P0
Possible causes for P0012-related issues include insufficient oil pressure, malfunctioning Oil Control Valve (OCV), VVT system stuck in retarded position, loose or damaged timing belt, or a potential PCM fault. While these are not exhaustive, they represent common root causes. A systematic step-by-step diagnosis is recommended to identify the exact source.
UPDATE: We've completed testing of the VVT solenoid (working), oil pressure (normal), oil level (correct), and sensor readings (all fine). The timing belt is tight with no visible tooth wear. Manual engine rotation revealed a small amount of oil dripping from under the timing chain, indicating possible actuator leakage or internal failure. We're now considering replacing the VVT actuator. However, I'm also concerned about long-term damage due to persistent knocking and rough idle — I’m seriously contemplating a full engine replacement.
The engine was replaced last month. It runs smoothly and idles like a kitten. This morning, however, a P0841 code appeared, and the transmission initially refused to engage gears. After further troubleshooting, it has returned to normal operation. Still, this highlights that even after resolving the P0012 issue, other systems may develop problems over time.
UPDATE: We tested the VVT solenoid and confirmed it is functioning properly. Oil pressure, oil level, and internal engine condition (no sludge) are all within normal ranges. Crankshaft and camshaft sensors have been checked — both appear to be working correctly. The VVT actuator was inspected; the timing belt is tight with no visible damage to the teeth. When manually turning the engine, a small amount of oil is observed leaking from beneath the timing chain. This suggests possible internal wear in the actuator. We're unsure whether replacing the VVT actuator will resolve the issue. Thoughts on next steps? Thanks again — chiggins