The oxygen sensor (O2S) on your Mazda Protege 5 must function properly to ensure that the right amount of air and fuel is delivered to the engine. A bad oxygen sensor may help introduce too much oxygen into the exhaust stream, increasing fuel consumption; or too little oxygen, increasing the poisonous gases released into the atmosphere. Moreover, a bad O2S will cause poor idle, acceleration and other engine performance problems. Keep your Mazda engine in shape by replacing the O2 sensor when it goes bad.
Start the engine and let it idle for about four minutes. Warming up the engine makes it easier to remove the oxygen sensor(s), especially the screw-in type, and keeps you from damaging the threads on the mounting boss.
Look for the oxygen sensor(s) you need to replace. The oxygen sensors are located on the exhaust pipes, before and after the catalytic converter.
Raise the front of your Protege 5, if necessary, using a floor jack and support it on 2 jack stands. Then apply the parking brake and chock the rear wheels.
Unplug the oxygen sensor electrical connector. On some Mazda Protege models, you will have to remove the passenger seat and the floor carpet to locate the downstream oxygen-sensor electrical connector.
Unscrew the two mounting bolts or nuts, using a ratchet and socket, and discard the socket if your vehicle uses the flange type sensor. For screw-in type units, use a box-end wrench or an oxygen-sensor socket to unscrew the sensor.
Set the new oxygen sensor in place. If you are replacing a flange type sensor, install a new gasket as well.
Apply a light coat of electrically conductive anti-seize compound to the threads of the mounting bolts/nuts or screw-in type sensor.
Start the two mounting bolts/nuts by hand, or screw in the sensor body by hand to avoid damage to the threads.
Tighten the two mounting bolts/nuts using the ratchet and socket, if you are replacing a flange type sensor; tighten the oxygen sensor with the box-end wrench or oxygen-sensor socket, if you are replacing a screw-in type sensor.
Plug in the oxygen-sensor electrical connector.
Replace the floor carpet and passenger seat if you had to remove them.
Lower the vehicle and remove the chocks.
