I have a 2000 ML320 and getting a PO400 code. Removed the tube and very little carbon so cleaned it and checked the EGR valve and attached solenoid valve and both functioned perfectly. Replaced the vacuum tubes on the valve and the one going to the intake, reset the codes and after 30 miles the light is back on. Is there anything else that is in the EGR circuit that might be causing this problem. I am thinking whatever controls the solenoid valve on the EGR. If so where would that be located? One last thing, if the codes are reset with a OBDII and cleared does that reset everything or is there additional procedures to completely eliminate the trouble codes?