About a year ago, my Check Engine Light came on and stayed on for a while. Dealer cleared it and told me I had not properly clicked down the gas cap. I did not think this was the case, since I am normally very careful, but I accepted the explanation.
Now, at the 3 year plus 2 month point, it happened again. This time, I presumed it was the gas cap, and decided to wait it out. Sure enough, about two weeks later, the light went out. I was able to notice the exact moment, and it occured while I was cruising along at about 20 mph in third gear. I have heard that there is a substantial number of defective gas caps, which is why that was my top suspicion. What to do..... I believe that the emissions control warranty is 5 years, so I find myself wondering if there is a good chance that my friendly neighborhood Honda dealer might be coerced into procuring a replacement for me, without much other evidence than my say-so.
How many of you fellow S2000 owners have had this problem? I should note that the car ran perfectly the whole time. I wonder if the fault is stored in memory after the light clears itself. Any thoughts out there?

 

This is a common problem with '02 and some '03 vehicles. I have had the same problem, and replacing the gas cap is only a temporary fix. I had mine replaced last year, and although my CEL hasn't come on since then, I've had to really crunch the cap closed to prevent the CEL from being triggered.

The problem is the fuel filler tube. It will likely need to be replaced. There are numerous posts talking about the subject if you do a search. Here is one that gives you information you can use when you go back to the dealer:

https://www.s2ki.com/forums/index.php?showtopic=226725

Pay particular attention to S2K Mayhem's advice on the last post. Let us know if you are successful in getting it replaced.

 

I have the same problem. When putting the cap back on, it starts clicking so you think it's on correctly. However, like the above poster said, the filler neck has a design flaw, so I have to keep pushing on the cap and it eventually settles into place and "clicks" at the correct location. Hopefully the dealer will replace the filler neck for me.

 

^^ I had the exact same problem and came to the same conclusion. For me however, it seems that after a couple months of fighting with it, the 'neck' has given way just enough for me to fully seal the gas cap without the need to exert as much force as before. No more CEL...

 

happened to me this weekend. as soon as the light came on, i knew what it was, because i had gotten gas about 50 miles ago. I screwed the cap down better, disconnected the battery to reset the ECU, and it hasn't come back on. Just make sure thats the first thing you check when you throw a CEL, because you don't want the dealer to charge you 90 dollars to diagonse the "problem"

 

Yup, this happens on my '02 also. Tightening the gas cap by grabbing the outer edge (rather than the "bar" in the middle) took care of the problem for about 40k miles. But now it's returning, and even tightening it using the outer edge doesn't always work anymore. I've personally been lazy about getting the filler neck replaced, but it looks like something that'll eventually need to be done.