A few months ago had error code P0266(No.2 cylinder) which I put down to bad fuel, as after a bottle of jet cleaner and a code reset, had no further problems. Today had error code P0263(No. 1 cylinder), again a bottle of jet cleaner and code reset and it too has gone. The fuel use has changed from a supermarket own brand to shell and BP ultra. Are these codes a sign of something possible worse?