Hyundai Repair: 2002 Accent check engine light, obd ii, compatible code

Question
My 2002 Accent check engine light came on recently. How can I check the diagnostic codes for this problem? Gas mileage dropped considerably and I seem to hear an exhaust leak.

Answer
And OBD-II compatible code reader is required to read the diagnostic trouble codes on your vehicle.  AutoZone and AAMCO have advertised they'll read your trouble codes for free.

I suspect you have code P0133.  If that's the case, repairing your exhaust leak will likely solve your issues.