230 K miles, running fine, threw a CEL just before I took it to the dealer to possibly trade it (it must have overheard me discussing this).

The first 2 codes indicate O2 sensors on opposite sides. I'm assuming that these codes are symptoms of something upstream. I have no personal experience with EGR valves, but from the reading I've done, it seems like the first things I should check for are blockages in the metal tube going from the EGR to the Intake manifold, or breaks in the plastic tube coming from the EGR.

Does this sound right - namely that I should ignore the P0130 and P0150 codes for the time being and focus on the P0400?

__________________
1996 C280 289K Traded
1997 E420 167K Traded
2001 S430 240K Traded
2010 E550 4matic 80K
2000 GMC Jimmy 198K Gone to Boneyard
2003 Camry LE 196K
2011 Mazda3 i Sport 31K

O2 sensors are designed for approx 120K miles.

Yes cleaning or replacing the EGR tube is a good starting point for P0 400

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator