So I've searched the forums for over an hour and I've had no luck in finding an answer to my question.

I have a MY2006 with 95,000 miles. All stock except for a cold air intake.

Yesterday (Monday) morning while on my commute to work my car Check Engine Light comes on. I go straight to the closest Midas and they pull this code: P0420 Catalyst System Efficiency Threshold (Bank 1). So I'm thinking great my catalytic converter is either on its way out or I have a faulty o2 sensor. I make an appointment with a reputable mechanic for this upcoming Thursday morning to have them take a look at it. Fast forward to today. My Check Engine Light decides to turn off by itself.

My question is, did whatever problem that was my ailing my S2000 just fix itself? Perhaps I had bad gas?

 

The criteria to complete the catalyst monitor on 06-09 is very sensitive. If conditions are just right, you can fail the monitor.

as long as it does not persist, you are fine.

 

Thanks Billman250! I appreciate the quick response. I finally have a sense of peace about my S.

 

Secondary o2 sensor issue:
CEL P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
Solution:
Many fix it with a $15 Blox spacer and it works for test pipes as well.
The ECU reflash in the TSB above may fix this as well. "The PGM-FI software has been changed to delay A/F sensor heater operation when there is a high probability of moisture on the A/F sensor."

https://www.s2ki.com/s2000/topic/954...ftware-update/