In Case You Get A Seemingly Random Check Engine Light

My T120 threw a check engine light two days ago. Googled wether I could read out the error code without an OBD scanner and well..you can. Just hold the i button while turning on the ignition and keep holding the button until you surpass the 'type' section and are greeted with any pending error code. P0053. Did some more googling which led me to believe that it most likely has something to do with an oxygen sensor. In some other forum someone spoke along the lines of an oxygen sensor readjustment. I thought about it. It did get a hell of a lot colder. Were down to around 5°C ambient temperature when I go to and from work. So could be that the ECU is re-adjusting for the drop in temperature. I was also ready to go to my dealer first thing next week. Now this morning suddenly when driving away from the supermarket on my way to work, I noticed, check engine light has gone out. Awesome! Also I noticed, fuel economy with the current tank is absolutely horrible. I wonder wether it has/had to do with the ECU having to re-adjust air/fuel mixture in order to compensate for the drop in ambients temps. Someone knows something about that? I would love to understand whats happening