My check engine light came on, I checked it and it is reading a DTC P0420. I'm thinking the code either means my pre-converter O2 sensor is gone or the converter is gone. But I am not finding any power loss while I'm driving or any excess exhaust. The check engine light came on after I filled up my car with gas, I wasn't sure if the gas condition would effect the converter's ability to clean up the exhaust. I was wondering if anyone could narrow the problem for me. I have purchased an O2 sensor but don't want to put it in yet until I know that could be the problem. Thank you for the advice.