I didn't have a check engine light at 78k. Probably an o2 sensor or something. If one of them dies, it throws a check engine and uses pre-coded fuel maps, so your car runs fine. Just tstop at your dealer and ask if they can read the code. If it is a o2, say thank you, order one from subaruparts.com and put it in. It'll take you 2 minutes to install.