The will be a code logged (ELM327 + smartphone app will tell you what it is) just wish that a button combination would show them on the car's display.
If there are no symptoms then it could be a connection plug on a sensor that's not making perfect contact, sometimes after service or under bonnet cleaning something might not be clicked back in place properly, or it could be a real fault. If concerned get it read at a garage, otherwise buy/borrow a code reader.
As it self-extinguishes then it must be something marginal rather than terminal, any commonality to the circumstances when it appears?
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TG