Dear Doctor: I have a 2005 Subaru Legacy GT (Turbo). I had the rear oxygen sensor replaced last year, drove 80 miles and it passed inspection. For most of this year the “check engine” light has been on so I replaced the front oxygen sensor. I put 390 miles on it and took it in for annual inspection and it failed. The mechanic said I should put more mileage on it. Codes did not clear yet. How many miles do I have to waste driving around before I pay more money to have it reinspected? Mitch
Dear Mitch: For an engine to set the computer monitors to pass state emissions inspection it has to meet many engine parameters. It is a “must” that the technician have knowledge of the system and use a professional scan tool. He can look at the vehicle computer in mode 6 where all information can be looked at and find the reason why your vehicle’s computer will not set the monitors to allow emissions passing. If there is a pending fault code or a circuit that is out of range, then it is possible that this will hold you back from passing.