Date registered: Jul 2015
Vehicle: 1997 C280
Location: California, USA
Mentioned: 0 Post(s)
Quoted: 20 Post(s)
You need to know the "Drive Cycle" for your Mercedes in order to clear your readiness monitors in the shortest amount of time. Google "Mercedes Drive Cycle" and try to find the one closest to your car. If you cannot find one, go to the dealer and ask for it. The drive cycle is a set of driving instructions that needs to be done in a certain order, certain speed for a certain amount of time. I have done this for my C-Class and I can clear them in about half an hour of driving around. You need to do this at a time of minimal traffic (like at late night time), otherwise you have to redo the drive cycle.
There is no reason to have your readiness monitor up and going unless you need to get a smog check soon. Also erasing codes with your OBD II scanner will cause all the readiness monitors to clear and not be ready, so try not to do that if not necessary. You will fail the smog check.
In California, you can still pass smog check if two readiness monitors are not yet ready. CA realizes it could take a long time to get them ready, like how you found out.