How to Install an Oxygen Sensor in an Audi A4

1. Raise the vehicle up in the air using the jack and secure it on jack stands. Double-check that the vehicle is secure before crawling underneath it.
2. Lay down on your back and slide underneath the vehicle. Locate the catalytic converter on the exhaust, which is close to the engine compartment and has large heat shields above and below it. They also have small louvers and holes in them. Just behind the catalytic converter is a small tube that protrudes perpendicular to the tubing, and has a small wiring harness coming out of it. Unplug that harness with your hands.
3. Unbolt the oxygen sensor from the exhaust using the oxygen sensor socket and the 3/8-inch ratchet. Once it's out, discard it.
4. Coat the threads on the replacement sensor with the anti-seize compound, making sure not to get it on the sensor body itself. Thread the replacement sensor into the bung on the exhaust by hand, then use the oxygen sensor socket and the ratchet to secure it in place. Clip the harness on the replacement sensor into the stock harness using your hands.
5. Drop the car off the jack stands using the jack.