[wolfox]

If memory serves correctly, there are two kinds of DTC codes set. A "hard" and a "soft" code. A soft code may or may not light the SES. A Hard one will will definitely light it. However, a hard fault will remain on until the problem is fixed. Soft codes can be stored and I do not think that they go away, just get overwritten in time. I am not positive about this, as my memory is quite foggy on this. I am sure someone else can speak up to clarify. However, since the code comes and goes seemingly randomly? I would just make sure all the plugs, hoses and sensors are tightly connected and clean under the hood. You may have an intermittent fault that just goes away when engine vibes wiggle a loose connection for you.