How to Replace the Oxygen Sensor in an E320


1. Park the vehicle, turn off the engine and open the hood. Detach the two small air pipes that run from the air box and the blowoff valves. Also remove the larger air pipe that's connected to the air box and the rear turbo. This will give you room to access the oxygen sensor, which is located on the precatalytic converter.
2. Spray some WD-40 on the old oxygen sensor to loosen it. Unscrew the sensor with the wrench to remove it from its port. Unhook the wires from the car's electrical wiring harness.
3. Connect the wires of the new oxygen sensor to the wiring harness. Apply a small amount of anti-seize paste to the threads of the new sensor. This will make removal easier for the next time. Be careful not to get any of the paste on the sensor itself or it could cause it to fail prematurely or not function properly.
4. Screw in the new oxygen sensor into the port and securely tighten it with the wrench. Connect the air pipes back onto the proper valves again.