Good afternoon my name is Tom Brintzenhofe, Certified Master Mechanic out of Reading, Pennsylvania and today I'm going to talk a little bit about troubleshooting oxygen sensor problems. Now oxygen sensor problems basically when you have an oxygen sensor problem you are going to have a check engine light. Some of the symptoms of having a bad oxygen sensor is 1) poor fuel economy, the second would be maybe a rougher idling engine, hesitation, stumbling, the biggest one is the check engine light. The only way to really diagnose a bad oxygen sensor is having diagnostic equipment that most shops have that is several thousand dollars to have this equipment. Real quick you could probably pull in to your local parts store, your Auto Zones, your Pep Boys might even actually come out and plug in their scanner and give you a code and tell you which oxygen sensor is bad. Outside of that taking it to your local garage they are going to charge you $70 to $80 just to hook it up and say hey you have got a bad oxygen sensor. Stop by your local parts store it is a lot cheaper. Other than the symptoms I told you before those are the key points. A lot of the Volkswagens if you have a Volkswagen and you are having an oxygen sensor problem you will know it because 90% of the time they don't run and they won't start. Other than that your key symptoms, your check engine light, your hesitation, your stumbling, rough idle and poor fuel economy, that's the biggest one. Other than that those are your biggest ways to troubleshoot a bad oxygen sensor.