Service light came on my ML350 and I took it to an independent shop. They diagnosed the problem in 15 minutes and mentioned that since it was only produced just one time just clearing the error would most likely be sufficient (for now), but if thrown again then replacing the emission sensor for $500 to $600 could be done. They, also mentioned that it might be worth checking (with Mercedes) as it might be covered under warranty or recall, as it was a faulty emission error.
I stopped by Grapevine Mercedes with the error codes, in hand, and they wanted $190 just to diagnose it. I agreed and sure enough they produced the same finding, but wanted $1,100 to correct the false error code and stated it needed to be done. All of that I guess is fine, but the process took them 3.5 hours. Honestly, I didn't feel my Service Adviser did any advising or analysis. My recommendation is to steer clear of their service department once you're car is outside of the warranty; find a good independent shop and save yourself time and $$$.
I'm currently starting a search for a new luxury car for my wife, but probably will eliminate Park Place and Mercedes from the equation based on their LACK of SERVICE. Just really disappointed in the experience, but I knew better...here's to hoping.