The oxygen sensor on the Silverado is a small electronic device hooked into the truck's exhaust manifold, and is used by the on-board computer to help monitor and regulate the mixture of air and fuel being pumped into the engine's combustion chambers. When an oxygen sensor goes bad, the computer cannot determine the correct mixture, and the output of harmful emissions is increased as a result. Fortunately, it is not an overly difficult process to replace a Silverado's oxygen sensor.
Locate the oxygen sensor you wish to replace. This can be done by beginning at the exhaust pipe at the rear of the Silverado and following it up toward the front of the truck. The 2002 Chevy Silverado actually has two oxygen sensors--unless the truck has been outfitted with a dual-exhaust, in which case it will have four, two identical sets on each exhaust system. These oxygen sensors are located on the exhaust manifold immediately before and just after the catalytic converter--the large boxy part attached to your exhaust manifold. The oxygen sensors will look like fat, round pegs with a cluster of wires coming out of the tips.
Follow the wires coming from the oxygen sensor's tip until you find where it connects into the Silverado's wiring harness. Unplug the sensor's wire from the harness, taking care not to damage the electrical connector on the truck itself.
Use your wrench or ratchet and socket--the ratchet and socket is generally the preferred method--to loosen and unscrew the sensor from the Silverado's exhaust manifold. You may need to exert substantial force to do this, as oxygen sensors often become stuck or "frozen" in place due to their being constantly exposed to high temperatures. You are free to discard the sensor once you've gotten it out.
Coat the screw threads of the new oxygen sensor with an anti-seize compound of your choice. This is both to ensure a smooth installation, and also to make it easier to remove the sensor when the time comes to replace it.
Screw the new sensor into the exhaust manifold and tighten it securely. Once this is done, plug the sensor's wires back into the Silverado's wiring harness via the electrical connector mentioned in Step 2.
Repeat steps 2-5 for the remaining oxygen sensors as necessary.
