The oxygen sensor measures the amount of unburned fuel in the exhaust pipe to adjust fuel mapping for cleaner emissions and better fuel economy. When malfunctioning, your MPG and performance can suffer due to lack of fuel or too much fuel depending on sensor readings. Replaced fairly easily, you can restore performance and fuel mileage quickly. Be sure to add anti-seize on the threads to prevent your new sensor from becoming a permanent part of the exhaust. For more ways to help bring you car back to life, check out the maintenance section for Ignition & Oil Service Kits. Regularly scheduled maintenance as O2 sensors tend to fail slowly.