There are a few symptoms that can develop in the E46 M3 relating to the vanos system over the course of ownership. If you experience a rattle or a constant check engine light relating to the vanos, you may be in store for some periodic maintenance.
The vanos solenoid packs tend to “fry” inside causing improper operation of the vanos solenoid pack. Other more involved repairs can be a broken cam gear or loosening vanos bolts. The cam gear bolts should also be checked during a valve cover replacement or valve adjustment.
The results of a broken cam gear can resemble our findings below. This usually will cause catastrophic engine damage. Typical replacement would be the vanos unit (we recommend Dr.Vanos solutions) for both the cam gear hub as well as the vanos unit. Dr. Vanos has re-drilled slightly smaller holes so the tabs sit more snug therefore the chance of failure due to smaller tolerances is less.