2003 BMW 325 Check Engine Light

My check engine light came on and the O2 after cat sensor was replaced. A week later the light came on when I started the engine on a 10 degree day. I heard a noticible ping in the engine as I turned the ignition then the light came on instantaneously. The error code was P1418. Local mechanic wasnt sure but changed a small airflow hose that was brittle. Any idea what the ping was. Thanks