I just had that same problem and it was driving me crazy. The Crossfire has 4 oxygen sensors. 2 pre-CATS & 2 post CATS. It turned out to be a crack in the CAT converter. It split at the weld point. The emission parts (CAT included) are covered by warranty for 8 yrs 80,000 miles. Chrysler replaced mine for free and I picked my car today. Runs GREAT and no check engine light.