i have a 94 e420 these codes reappeared 4,6,17,19,20 can someone help me with them. [1] code 4 is dealing with oxygen sensor if iam correct just put a new one on the car about 2 weeks ago. [2] code 6 is dealing with the diagnostic module. [3] code 17 coolant i will check the ratio of antifreeze to water tommorow to see where it is at. [4] code 19 is dealing with a tapping noise which i here on the driver side. i have a valve covers set and i just changed oil 2 wks ago i used 10w30 mobil 1 but i still here tapping will pull valve cover this wkend n check the oil tubes. what is part # for chain tensioner clamp. [5] code viscous fan clutch. also my a/c started to blown warm air to day. i noticed a week or so ago that my window would have a mist or condensation on it will this be coming from low freon. any sugestion will really help please. temp here is around 90 plus degrees with high humidty