1998 Subaru Legacy

Replacing an oxygen sensor is not much more difficult than changing a sparkplug. Here are some tips that will make it easier to replace an oxygen sensor:

Go by the book. Make sure to consult a service manual for your vehicle before attempting to replace an oxygen sensor.
Down below. You'll need to work underneath the car to replace an oxygen sensor. Always use jack stands rated for your vehicle and to chock any wheels left on the ground.
Safety first. Protective eyewear is a must. Take special care, just as you would any time you work near the exhaust system, which can get hot and dangerous.
Preparing for removal. Once, you've located the oxygen sensor to be replaced, spray the threaded area with a penetrating lubricant. While the lubricant loosens the connection, carefully disconnect the wiring harness and place it aside.
Out with the old. Using a flared or box-end wrench, loosen and remove the old sensor. Some oxygen sensors may require a special socket to accommodate wiring locations-your service manual will alert you to these situations.
In with the new. New Bosch oxygen sensors come with a special anti-seize compound applied to the threads. Simply position the new sensors in the threaded hole and tighten in place. There's no need to over-tighten the sensor-just past hand tight should be fine. One the plug is in place, re-attach the wiring harness.

Your vehicle has 2. They are on the exhaust system. 1 is on the front catalytic converter inlet and the 2nd is on the rear catalytic converter.