S1, S2 ,exhaust... any modsglhs837 said:Not so, depending on what you mean by mods. At 30K, I had my plugs and wires replaced under TSB with S1 installed. The tech asked me about the P0633 code, I explained it, and away we went on the diagnostic test drive. I'll be seeing them tommorow about carbo tracking on the plugs they put in then. I'll report back.