I bought my car at 60k, it ran beautifully. Then when it reached 65k, check engine light turns on. What I did was to borrow the code reader from Autozones, found out that my sensor at the catalyst or the catalyst was bad ( i forgot which).
I did some research and found out that the car is still under warranty. I am the second owner, and I called the 1st owner for permission if I could use his name for the service, he said ok. I took it to the Honda Dealer and said I'm the first owner's brother. They check his name and the VIN, and guess what, they replaced the cat for free.

If your car is still under 70k or 80k, you might still have warranty for the emission system