- 2014 Buick Encore
2014 Encore, about 70,000 miles, steady Check Engine Light. Mechanic replaced the coil ($388). Light still comes on. Car has a slightly rough idle but drives okay. After driving a few miles there is a roaring sound which seems to be coming from the serpentine belt end of the engine. Alternator? Serpentine belt idler? I plan to take it back to the mechanic. I don't have a scanner. Should I buy one? Take it to Auto Zone and get it read, then back to the mechanic?