2014 diesel with 38,000 miles. I've only had the car a few weeks and the CEL comes on. I took it to the dealer as they put a "peace of mind dealership warranty on all newer used cars they sell. First they check it out and say that it needs a new fuel filter and they would go ahead and take care of it for me. Once they start to replace it they then tell me that they found out they need a new part for the replacement but that it's be covered under the GM factory 100,000 powertrain warranty. She then tells me I lucked out because the part was $1,300. The part is ordered and I'm not paying a penny but I'm so very curious what in the heck could be going on with it. Does anyone have a clue? The invoice says "1- 23199833 F- (S) Converter" as the part ordered. Thanks for any help!