The Mercedes-Benz oxygen sensor in your exhaust system is supplying data about the surrounding atmosphere compared to the composition of your exhaust gases as you drive down the road. This data is used by the onboard computer to determine the correct air to fuel mixture that each cylinder should be receiving. The actual task the oxygen sensor performs is the direct comparison of the oxygen level in the surrounding atmosphere to what your Mercedes-Benz engine is producing. This will ultimately adjust the air/fuel ratio slightly as the vehicle is driving through heavy smog conditions or at high altitudes, because lower levels of useable oxygen for the engine are present in the air. The oxygen sensor can be seen by looking at the exhaust pipe just behind the exhaust manifold. It looks like a simple sensor with a wire sticking out of it. This placement is the best position for an accurate reading of what is present in the exhaust gases your engine is producing in real time. While the level of oxygen change is very minute, the onboard computer will make the correct adjustment so your Mercedes-Benz engine will be able to perform at it maximum performance level and provide the owner with the best possible fuel mileage when it is operating correctly. The failing of the Mercedes-Benz oxygen sensor is indicated to the owner of the vehicle by the illumination of the check engine light on the dash board. Once the code is retrieved for the onboard computer indicating the oxygen sensor as the failing component, it can be easily replaced on your Mercedes-Benz. By disconnecting the battery before the oxygen sensor is replaced, there will be no danger of an electrical shock occurring to the technician. This will also clear the codes that were stored in the onboard computer.