engine light is on car runs fine but exhaust stinks

I have a 98 escort wagon 4cyl with 150 thousand miles. The check engine light recently came on the exhaust smells but it runs fine.It dosen't chug or sputter it is overdue for an oil change. I recently installed new plugs and wires. What is the problem???

Go to autozone. They'll check your code(s) for free.

It might be your oxygen sensor