The iCarSoft MBII did not turn up the P24AF code. When I asked at the MB Dealer what this code means they said they had no idea and that it was a generic OBDII code with no meaning to MB.

It seems there are two sensors that could be the root cause of the warning light and why I can't get through NJ State inspection. The car runs as great as it always has.

The differential pressure sensor is part A642 905 02 00. It is available at a price range of about $30 up to $108 at the MB dealer.
The nitrogen oxides (NOx) sensor is A000 905 35 03 and is available from about $240 on-line up to $560 at the MB dealer.

Before I spend money in throwing parts at this I will remove the engine cover and look around carefully to see if there is another obvious cause...such as a broken wire, loose or dirty connector, etc.

Onward!

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2014 E250 Bluetec 4-Matic
2014 GL350 Bluetec 4-Matic
1996 Chevy Tahoe 4 x 4
2009 ML350 (sold)
2005 SLK350 (sold)
1999 E300 Turbodiesel (sold)
1998 ML320 (sold)
1991 300D 2.5 Turbodiesel (sold)