My 1994 E320 wagon have this self test diagnostic module (DM) 16-pin rectangular box located in front of the battery. The wagon works and drives fine with no check engine light on. Just to check the diagnostic module to see if there are any codes, I tried to push the button to give me codes. The red light was on when pressed and when I released the button after holding the button for 3 to 5 seconds, no flash or blinking codes. The same thing happen when I use the code reader as well. I even tried to use the HFM software scan and came up with no connections, either. Something is missing that is not producing the flash/blinking codes. I searched this forum and so far, I don't see any real issue with the self-test diagnostic module problems. The Over Protection Relay (OVP)is good, no broken fuses that I can think of. The wiring harness is good and not bio junk. Anyone have this problem? Feedback and/or comments is greatly appreciated. Thanks for reading.