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A poorly running engine will cause excessive mixture swings that will trigger a converter code. It may smell of sulphur also. Fixing the mixture problem will cause the code to go away in such a case.
It is advised though that a Ford dealership test the convertor if it is in question. If it checks good you will be charged, but if it tests bad it can then be replaced under warranty.
The third option is to ditch the pre-cat yourself and bypass the downstream O2 sensors. The main CAT can handle the job except during warmup and the car will still pass emissions tests.
