A faulty oxygen sensor can have one of the most detrimental effects on gas mileage. Fuel efficiency losses of up to 40% are not uncommon if your O2 sensor is damaged or malfunctioning. Gas mileage losses can occur with sensors that are just old, worn, and not outputting voltages properly. The oxygen sensor in your vehicle outputs a voltage to your car’s computer based on the amount of oxygen in your combusted air fuel mixture. If the O2 sensor is malfunctioning, it may be falsely alerting your ECU by telling it there is too much oxygen in your exhaust when there really isn’t. This causes your system to dump more fuel into your air fuel mixture wasting excess gas and destroying your fuel economy.
1. When to Change your Oxygen Sensor
The life cycle of an oxygen sensor varies depending on the brand, its specifications, and the environment it will experience during its use. We have found manufacturer claims of anywhere between 15,000 to 30,000 miles on older vehicles to greater than 60,000 miles on newer vehicles. If your fuel economy has dropped significantly from its stock rating and all other causes have been ruled out such as vacuum leaks, exhaust restrictions, etc. then it is a good possibility your oxygen sensor is to blame.
2. What sensors to buy
When replacing oxygen sensors we recommend not straying from manufacturer recommended replacement units. Standard automotive accessory stores such as AutoZone and Consumer Auto Parts should be able to match up the correct oxygen sensor for your vehicle based on the make, model, and year. The main concern here is to buy a sensor with the same operating specifications as the unit your vehicle was designed to operate with. Otherwise you could be doing more harm than good by installing an incorrect range.
We have seen an improvement in fuel economy of 15-18% by replacing an oxygen sensor on a 91 Ford Mercury with 127,000 miles on it. Remember that it takes a while for the air fuel ratio to adjust when making a change such as a faulty O2 sensor. So when making this modification, note that it may take a few weeks for your fuel economy to reach its new optimal level.