I'm curious to know if codes aren't resetted, are they stored on memory even when it no longer shows the Service Engine Soon light? Reason I ask is because today I got a CEL and had two codes, P0420 (cat below threshold) and P0314 (Heated Oxygen Sensor No Activity Detected) and I know perfectly well that my cat is working right considering I haven't touched it and I only have about 2900 miles, but at one point (2 weeks ago) one of my clamps blew off and triggered the CEL, but the next morning the CEL went away, so I was wondering if that CEL was stored on memory.

And also, is it possible that P0314 can be triggered by a loose gas cap? After I had the codes resetted by an OBD2 scanner, no CEL's popped up and I had tightened my gas cap as it was loose.

By the way, when the codes came on, the car still ran fine and idled fine as if nothing happened. Only thing I have done to the car is a custom Dynoflash.

Thanks.

 

Codes are stored.