A car's O2 sensor is a main component in keeping your car in smooth-running order. There are many warning signs that are caused by problems with your O2 sensor and the following will help you diagnose what those symptoms are and how they affect your driving.
The O2 sensor often times is the main problem with bad fuel economy. While other parts of the car may hinder your gas mileage, if you are noticing that it hasn't improved after a tune up, it may be a problem caused by the O2 sensor. The O2 sensor is designed to send an electric impulse to the car's computer when there's more fuel in the air/fuel ratio. If the sensor has worn out or has stopped working, then the air/fuel ratio will be incorrect and extra gas will be used, causing your car to run "rich."
This problem causes more than just poor fuel economy. The extra fuel can cause misfires from your spark plugs becoming saturated with the extra gas along with backfires from your exhaust as the unused gas ignites once it exits the engine. Once your car begins to misfire, the check engine light will automatically alert you that something is wrong but it will come up as a misfire which it very well could be. The easiest way to tell what the problem is would be to first check your spark plugs. If they are still good, then getting your O2 sensor would be the next step.
Misfiring and backfiring are bad not only for the car's combustion but also for the environment as they let out smoke and combustion into the air increasing hydrocarbons and bad gases which the emission laws prohibit. For people in jurisdictions with strict emissions laws, having a bad O2 sensor could very well cause your car to fail its emissions test. The problem will have to be fixed before your car passes the test.
