EML light on a 2010 fiesta

[Maxfu7]

I’ve been left pulling my hair out over an Engine management light on my 2010 1.6 petrol fiesta.. every time I’ve plugged it into a computer it’s had the same results: “mixture too rich - code P0172” 

the car is on 80k miles. I’ve had a new OE sensor. New spark plugs. Full service with no expense shared. New MAF Sensor. And no doubt a few I’ve forgotten. Best hope was the OE sensor as it turned off the light and stayed off for the longest time before returning. 

Any advice would be great because it’s just something I need fixed!

[isetta]

is oe sensor the oxygen sensor in the exhaust? years ago I had a Ford Escort that failed MOT on the emmissions being far too high. It turned out to be  faulty oxygen sensor. But when I was trying to get to the bottom of it, I had a garage plug a thing in the OBD port which monitored loads of stuff live as engine was running (this was before I had my own OBD code reader and Forscan software). One of the things he was showing me was the voltage output from the oxygen sensor, he said this was far too low (I think low and not high) and was causing it to run very rich as the ECU wasn't being told to reduce fuel to air ratio.  I do not know if Forscan will give a live reading of oxygen sensor voltage but it might be an idea to see what voltage output is shown from it to try to judge if that is the problem part. (I do not know what normal voltage should be but I am guessing google would perhaps reveal some info)