An oxygen sensor, or O2 sensor as it is also called, is a small device that your vehicle's onboard computer uses to monitor and adjust the air-to-fuel ratio that gets pumped into your engine. It does this by monitoring emissions flowing out of your car's exhaust and making the appropriate adjustments electronically. When an oxygen sensor goes bad, it often causes an imbalance in the air-to-fuel ratio, which results in increased emissions. That can be a true headache when time for a smog check rolls around. Fortunately, the O2 sensor on a 2000 Chevrolet Impala is not especially difficult--or particularly expensive--to replace.
Locate the oxygen sensor. The 2000 Chevy Impala has two of them, immediately behind and just in front of the catalytic converter on the exhaust manifold. Look for an object that appears to be a golden or brass peg with wires coming out of the tip.
Disconnect the wires that run from the O2 sensor into the Chevy's electrical system from the electrical socket on your car. Take care; damaging the electrical socket may cause the new O2 sensor to not draw power correctly.
Use a ratchet and 22 mm socket (or a 22 mm wrench) to unscrew the O2 sensor from where it is mounted on the exhaust manifold. You may need to use significant force, as the O2 sensor's location on the manifold, near the high heat and proximity to your car's emissions, often causes the sensor to get stuck.
Coat the threads of the new O2 sensor with WD-40 or a similar lubricant, then do the same to the threads in the hole where you just removed the old sensor.
Screw in the new O2 sensor and tighten it securely in place on the Impala. Plug the new sensor's wires back into the electrical system via the socket.
