Check engine light went off

[Geodesiq]

My check engine light came on, the dealer said it needs a new cat. A few days later the light went off. Sup widdat? It cured itself!

[gilbertguy]

The way I understand the CEL is that if you have 3 cold starts without the issue that set the light in the first place then the computer will turn the CEL light off. So what that could mean is your issue isn't that bad right now and the computer saw some kind of spike in the CAT that set the light, I'd call it good for now until the issue turns the CEL light on for good.

[Artric]

When the cats go bad, do they cause the car to not run properly? Is lean burn no longer possible? Curious if it's really a necessity to change.