The O2 sensor is a device found on all modern production vehicles that monitors a vehicle's emissions. O2 sensors send information about the emissions to the vehicle's computer. The computer then adjusts the air-to-fuel ratio in an attempt to optimize it as well as optimize power and fuel efficiency. After 100,000 miles, these sensors begin to fail on many vehicles, though there is no set lifetime for the sensors. You will likely want to troubleshoot the problem in order to know whether or not your O2 sensor is bad.
Raise the vehicle on jack stands so that you can access the O2 sensor under the vehicle. Jack up the vehicle with the floor jack using the front jack point behind the radiator. If your vehicle sits high enough off the ground and you can access the sensor without lifting it up, skip this step.
Climb under the vehicle and remove the electrical connection to the O2 sensor by squeezing the release tab and pulling the connector off the O2 sensor.
Touch the red lead of the voltmeter to the feedback wire on the O2 sensor and the black lead to the ground on the sensor.
Select the "millivolt" option on your voltmeter.
Start the engine. Run it at idle until it warms up to normal operating temperature.
Check the voltmeter. It should fluctuate slightly before settling to 150 millivolts. Rev the engine or have an assistant do so while you check the voltmeter. It should drop momentarily before reading slightly higher than 150 millivolts, and then it should return to the 150 millivolt reading. If it does not cycle in this manner, then the sensor needs to be replaced.
