It may be a mantainence item BUT in my 350K, not once did the O2 sensor light indicate to me that the O2 sensor was bad. And not once did the car fail an emission test. Just lost power gradually likely because of oil burning, and inspite of continuously degrading CAT, the emission was just fine. Plus when I tested the sensor output, it did modulate the output between 0.1 and 0.9V that mercedes manual says is a test for a good O2 sensor. At the same time I agree that the rate at which the O2 sensor responds to changes in oxygen is critical, and if this response rate is not adequate then the output of the oxygen sensor will not be accurate and the computer will make an inaccurate mixture adjustment. BUT if the lag is too big, at some point the O2 sensor output will go out of the limits. And if the voltage remains in the correct range, I am not sure if the problem is that significant.

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Saumil S. Patel