The oxygen sensor on your Mercedes C320 should last in excess of 100,000 miles. It uses several lead wires to provide power to the sensor as opposed to a single wire. Replacement oxygen sensors are available from a Mercedes dealership and from some auto parts stores. The sensor for your C320 will monitor the exhaust gases from the engine and send this information to the vehicle's computer. The computer can then make adjustments to the air to fuel ratio. When this sensor fails, your Mercedes will show a marked decrease in engine performance.
Jack up the front of the C320 using a floor jack under the front jack point behind the radiator.
Place jack stands under the frame of the vehicle and lower the C320 onto the stands.
Climb under the vehicle and locate the oxygen sensors on the exhaust. They will look like small plugs screwed into the exhaust. There will be one before the catalytic converter and one after it.
Unplug the leads running to the oxygen sensors.
Unbolt the oxygen sensors using an O2 sensor socket and socket wrench.
Thread and tighten the replacement oxygen sensors and lower the C320 to the ground. Installation is the reverse of removal.