Check engine light keeps coming on.

I have a 2007 Cayman S that I have owned since new. About a week ago I got a check engine light. When a OBD2 scanner was connected to it, the only thing that came up were two errors that said: Major fuel leak, gas tank leak". The thing is that there is no major fuel leak or gas tank leak. There is no evidence of fuel on the ground, no increased consumption of fuel, no gas smell, and the car runs great as always. I thought that maybe the gas cap was not in properly so I opened it and re installed it. While the scanner was connected, the computer was reset and the error message obviously went away. A couple of days later the check engine message comes back for the same reason. Has anyone else have had this happened? I am wondering if it may be a faulty gas cap. Any and all ideas/suggestions welcomed. Bill.

If the message went away for a couple days then returned I'd look closer at the cap because if the cap had no connection you would think the code would have re-thrown immediately. Obligatory how old is the battery sentence too.

Hi Boris, thanks for you comments. I am suspicious of the gas cap as well. As for the battery, the one in the car now is a few years old, but I don't think it is the battery. In the past when the battery has been weak the issue was with getting the car started. It would turn a few times before starting. I just don't understand what could be going on with the gas cap to cause the error code.

You can get a free battery load test at a parts store, it's more accurate than acid assessment or other means, ruling stuff out free is always a plus. You see a lot of reports of crazy codes with failing batteries. The other good thing is a gas cap is an easy exchange and if you're wrong you wagered the cost of a cocktail at any bar unless you want the fancy aluminum unit you can't see anyway.

That is a good idea. A battery load test would confirm or rule out the battery as a possible reason for the engine light. Thanks again. Bill.

Load test on the battery is certainly better than other methods, but I have seen even load-tested batteries causing issues on these cars. They're just hyper-sensitive to battery issues. If the battery has ever been dead then I'd replace it within 3 years. If it's been taken care of, then you could make it to 5 years (assuming it's the correct battery type for your region - ie, northern battery in the north, southern battery in the south). As for the scanner, it's best to tell us the code you're seeing. Certain code ranges are manufacturer-specific (P1000+ for example) so you can't trust generic scanners to interpret the number properly. Don't get me wrong, the number will read properly, but the meaning can vary. For this reason, it's important to know what the actual code was... do you know which one it is? I agree, likely it's a gas cap, but it could be other things. Do you top off your gas tank? This can cause problems with the gas venting system and damage things, which is why it's best never to do that. If something there is damaged, then that could be another cause of a gas-related code.

Schwinn, Thanks for responding. The car is on its third battery including the one that came with the car originally. It has been in the car a few years, and it has never been dead. I will call the local Porsche shop that did the scanning and ask them what the actual code was. I have to admit that I do top of the gas tank. I guess I should stop doing that. Bill.

Replace the gas cap as it's an inexpensive attempt to solve the problem and in my opinion, the cause of your problem.

Thanks Budman. I am definitely getting a new gas cap. It has done its job well for 15 years. I guess it's time to replace it. Thanks.

Check the date code on the battery - installation date might be close to the manufacture date, but it also could be way off. For the topoff issue, here's one reference (there are plenty more out there if you want to read more about it): Should You Top Off Your Car’s Gas Tank?

Thank you, Schwinn. I will check the battery date when I get home, and will be going to a part store to have a load test on the battery. In a previous post you asked for the code number for the fault codes. I called the shop and these are the numbers. P0455 - Tank system major leak. But there is no visible fuel leak, much less a major one. P0461 - Fuel level sensor. This one may have something to do with the fact that I keep filling the tank to the very top. I'll keep posting as I rule out possible probable causes until the problem is solved.

I think you are taking the error code of "major tank leak" too literally. You could drill a hole in the gas tank and all the gas drain out in your driveway, but the cars system wouldn't know anything happened, nor does it care. All it would know is that the tank is now empty on the gauge no differently than driving the fuel out. Its most likely a major vacuum leak or venting issue that its referring to which IS something that will trigger a fault code in the system, taking us back again to either the cap not sealing properly or a tank venting issue of some sort.

I'm not so sure about drilling a hole in the gas tank. Part of the emissions check system is pulling a light vacuum on the fuel tank (which also checks the fuel cap) and a hole in the tank would certainly cause an emissions error. I do think a new fuel cap at this age/mileage isn't unreasonable. I had issues like this on my 2001 M-Coupe about 5 years ago, and I examined the cap carefully. The rubber seal on it had hairline cracks in it. Some Gummi-Pflege (silicone grease) rubbed into the cracks to seal them up cleared the error code long enough for me to locate and buy a new cap. If you have a tube of Gummi-Pflege nextzett Gummi Pflege Rubber Care Stick - Google Search - that might be worth a try to confirm it is the cap. Don't use more than absolutely needed, you don't want it to get into the fuel system, it will poison the O2 sensors and MAF. (Doesn't everyone have Gummi-Pflege in their German car? The rubber seals love it and last about forever - even in California - if it's rubbed into them periodically.)

Hi deilenbeger, The gas cap seems to be accused the most, so I have already ordered a new gas cap, but I won't get it till next week. I am working away from home this week so the battery check will have to wait for next week as well. I see you have an Jag E-Type as your avatar. Do you have one?

Hi Daytona. Not sure if this will help, but I went through the same thing on a Honda Pilot about a year ago. The code was for an evaporative system leak. It would trigger the check engine light about 50 miles after I cleared it. Nothing obvious was wrong, and I eventually bought a smoke generator to help search for it. That immediately revealed a leak in one of the purge lines, naturally in an inaccessible spot on top of the tank!

Hi A&Mengineer81, All information helps. For now I will change the gas cap and check the battery as these seem to be the most likely culprits, and the easiest to do. If they don't resolve the issue then I'll have to get deeper into it. Thanks.

Yes, my post was more over the top tongue and cheek. The point being the error code isnt telling you that you have a major "gas leak" so you aren't going to see fuel leaking on the floor anywhere.

I agree gas cap is likely the issue. If not the carbon filter can be damaged by topping off which will throw a code. Battery is doubtful (but not impossible) because you get the code while driving when voltage is up. Be sure to let us know what it was when you solve it.

The Porsche "fancy aluminium unit" is a fancy plastic unit with an aluminium look finish. Disappointing. I believe that this is also the case for my fancy SportDesign steering wheel.