Both cars of mine had this problem. The problem on my Nissan was fixed. A new sensor was installed to replace the mul-function one in February. The warning light has not lit since then. The light on my Mazda comes on intermitantly after a tuning at the Midas shop on Bronson Street. I was told by a mechanic there up to 4 sensors need to be replaced when I questioned the effectiveness of the tuning. So I gave up. The problem has lasted for 2 years but does not cause any trouble. Anyway, it seems that this is a sensor problem but not an engine problem.
labor is only $5 per hour cheaper than dealer comparing to Ford. It is $95 an hour at CT. The answer is very obvious. Further, I suggest you replace with orignal parts as far as electronics device is concern. The differences are the quality, good fit and no worry.