A Honda Civic has two sensors that read oxygen levels in the exhaust when the engine is running. The oxygen level data is used by a Honda Civic's computer to control fuel supply and ignition. Located before and after the catalytic converters, the sensors can go bad and cause the engine to run poorly. A bad oxygen sensor can result in an engine light that tells you something needs to be fixed--a poor-running engine that blows smoke out the tailpipe, fails an emissions test or doesn't run at all. Change an oxygen sensor on a Honda Civic using an oxygen sensor socket and some penetrating oil.
Apply penetrating oil around the base of the bad oxygen sensor where it threads into the exhaust pipe or exhaust manifold. The Honda Civic has two sensors that monitor exhaust gases produced by the engine during operation. One sensor is located before the catalytic converter and one is after. The one before can be found sticking out of the exhaust manifold and the other out of the exhaust by the mufflers. Depending on which sensor is bad, you will be working either inside the engine compartment or underneath the vehicle.
Disconnect an oxygen sensor from the wiring harness at the wiring adaptor that holds it in place. The wiring adaptor has a tab that locks two connectors together, and it needs to be unlatched to separate the sensor connector from the harness connector. Lift the locking tab and pull the adaptors apart. The sensor and its wire can be removed without twisting any harness wires as the sensor is turned inside the threaded collar when removed.
Place an oxygen sensor socket over the top of the sensor. These sockets have a space for the sensor wire to pass through the side of the socket, allowing the socket to be placed around the sensor and the sensor to be loosened from its position in the sensor-mounting collar. Turn the socket counterclockwise to loosen the sensor within its threaded mounting collar.
Disconnect the socket from around the sensor when it has become loose enough to remove by hand, or continue to turn the socket and the sensor counterclockwise until it is free from the threaded collar holding it in place.
Remove the sensor and discard properly. Oxygen sensors use precious metals to read the oxygen levels in exhaust gases. These sensors should be recycled properly.
Insert a new oxygen sensor into the threaded sensor collar by hand until it is tight. Place the sensor socket over the top of the new sensor, and use the ratcheting wrench to continue tightening. When the sensor has been tightened securely, connect the new sensor to the old wiring harness using the new sensor's wiring adaptor.
On hard-to-remove sensors, use a torch to gently heat the threaded collar the sensor is in to help loosen the sensor for removal. Heat will expand the collar enough to let the threads of the sensor become free from the threaded collar. If you do not have a torch, run the car to its operating temperature.
A Honda Civic's exhaust will be extremely hot if you run the car before changing oxygen sensors. Because most sensors are hard to remove, heat is usually applied to get them free. When heat is added to the exhaust, it becomes hot enough to burn skin long after the heat has been applied. Avoid contact burns by wearing gloves and protective clothing.