It looks a plug of some sort. Funny(now) and scary(pissed off) story to tell. My wife took her 2006 Chevy Cobalt to the dealership for a routine oil change/tire rotation. They called her name in the waiting area, her car was ready, she paid, she drove off. Not less than a few blocks from the dealership, she gets a check engine light, oil pressure light. She pulls over, and calls the dealership and tells them she thinks they forgot to put oil in after the oil change. They send a tech and he puts oil in and they tow the car back to the dealership. The engine had already seized running with no oil. Long story short, they replace the engine with a refurbished engine with 60,000 miles(wife had 120,000 miles on old engine), and as a courtesy they fixed her drivers side window which wasn't working. Before anyone states that they would have demanded a new engine, or money for time lost, the laws are written for corporations, it would have been a waste of money and time to pursue this any further with attorneys. It took them almost a month to find an engine and replace it. That was a year ago and her car runs like new now, well almost