Why is my 2009 GMC Acadia check engine light flashing?

While the check engine light illuminating is a pretty common and nonspecific indicator, when it begins flashing, You're almost always looking at engine mIS Fires. Now, these can be caused by a number of different things in Your 2009 GMC Acadia, but at the end of the day, the diagnosis is all the same: stop driving Your vehicle until You get it fixed. Driving on mIS Fires doesn't just feELRough and jerky; You're likely also causing long term damage to Your engine. While it's "safe" (ish) to drive Your Acadia home if this happens while You're on the road, You'll want to get the system diagnosed as soon as possible and not drive the vehicle until You do. Fixes may come cheaply, but they can also run You into the hundreds of dollars, depending on cause.