Check Engine Light

Hi All, my 2005 120i threw up a Check Engine light yesterday. It's still running beautifully & economy is excellent. I suspect it could be the 91 ULP I put in it the day before. Usually use 98. My previous VW Polo's light could be reset by disconnecting then reconnecting the battery. Can I do this on my 120i & will it cause any issues? 

Oh, other variation is that BMW replaced the Driver's airbag on Wednesday & I presume that they'd've disconnected the battery to do that.

Thanks in advance.