My check engine light came on with code 45. I'm running lean. I do know that I had an exhaust leak last earlier this year and one of the wire was melted. I replaced the O2 wire, but I do know that for a few months the O2 sensor wasn't working correctly. So I'm thinking the O2 sensor is damaged.

What would you guys suggest? Is it bad to run lean? My mech did replace the fuel filter cause it was clogged, the fuel pump is fine.