Hey Guys,

I am new to the Miata game sorry. I have a 1999 mazda miata that I got 3 weeks ago. I was driving one day from work and I got a check engine light. So I did a oil change, changed my spark plugs, and also checked the gas gap. I reset the check engine light by disconnect and reconnect the battery. My check engine light came on again couple days ago. I went to Pep boys and they read it for me and it said Code PO421. What can I do to fix this? I heard my car is a CA-SPEC car. Please help