Even if you have no codes, you will get a long confirmation beep and it will say END which lets you know you have no active codes. If you shut if off, and put the key back on and it is no longer in limp mode, that means the code is no longer active and won't come up when pressing set 5 times. You have to do it while the problem is happening or active. If you want to see codes that are not active, you'll need BUDS or CanDoo, but inactive codes mean very little if it's running fine and most skis have plenty of inactive codes, so many that normally you have to clear them and get it to do the problem again before you really know what it is.
Which oil pressure sensor did you change? If you didn't change the rear one, it is unlikely that you solved the problem. I did a pretty thorough explanation of this in someone's post a few years ago, do a search.