I replaced the O2 sensors on my 2001 C240. I also replaced my MAF sensor and EGR valve. The car has 130K miles and had multiple OBD codes, and this fixed them all, the car runs great. However, lately after I drive the car for an hour or so I get codes P2096 and P2099 on both O2 banks. I clear the codes and they re-appear after driving an hour or so. I just bought a Bluetooth OBD transmitter and downloaded Dash Command onto my iPhone and now can directly read the voltage levels of all four sensors. Problem is, I don't know what to look for. Does anyone know what the voltage readings should be for the upstream and downstream sensors for this car?