lately my car has been getting the check engine light. I open the bonnet and it's still there .... it's a VY S2 calais LS1 so seriously I'm thinking it could be a faulty oxygen sensor it does it when the motors hot or cold. mainly when I'm going slow like in a car park. Most of the time before it happens i notice the instant fuel usage can climb to over 50L/100km and it starts running rough the light comes on. If the light is on and I get it cruising on the open road it seems to dissappear. like not go to the small icon on the side of the dash but completely removed from the display. I assume it must fix itself when it's basically running at a constant speed. I have taken it to holden dealer but they said they can only do a scan if the light is flashing. worst thing is I haven't been able to get it to come on when holden are open. I did replace the oxygen sensors 2 yrs(10k) ago. (One of them is a prick to change) I still have my old ones if the scan shows it is that can i put an old one in or should I get 2 more new ones? I have heard swapping sides can fix it? or any other ideas?