The oxygen sensor is part of an engine's computer controls. The sensor monitors the oxygen levels in the vehicle's exhaust system and sends this data to the main engine computer. The computer analyzes the information and uses it to adjust the air-to-fuel mixture according to temperature, engine and vehicle speed to insure that as little unburned mixture exits the engine as possible. An oxygen sensor that is not operating properly may increase engine emissions, lower fuel mileage or cause the engine to run erratically.
Turn off the engine and open the hood. Allow the engine to cool if it has been run recently.
Locate the exhaust manifold, which is a cast-iron part mounted on the engine block to which the exhaust pipe is bolted. Look for the manifold on the side of the engine block for longitudinally mounted engines and at the front of the block for transverse-mounted engines.
Check the surface of the exhaust manifold for the oxygen sensor, which is threaded into the manifold and has a wiring connector attached to it. Close the hood.
Drive the vehicle onto a set of car ramps to locate the oxygen sensor if it is not mounted to the exhaust manifold. Set the parking brake.
Crawl under the vehicle on the driver's side and locate the catalytic converter, which is mounted inline with the exhaust pipe. Check the surface of the converter and the exhaust pipe near the converter for the oxygen sensor. Carefully back the vehicle off the car ramps.
