rqw101

My '95 C280 with 135K has never run better or gotten better mileage but I can't get the CEL to stop coming on. The EGR valve, changeover valve and charcoal canister have been replaced and vacuum lines have been cleaned out plus a fuel cleaner similar to Seafoam has been run thru the system. You can re-set the CEL but after a few weeks it re-appears withe same code which if I remember is 0400. The guy I use is an ex MBZ tech and says he can't do anything else and suggests either living with the problem or having the dealer analyze it(I'd opt for a root canal first!).
Thanks for any and all suggestions