I have a stock, 2007 convertible whose check engine light is on with a code indicating the gas cap is off/loose. According to my mechanic, the cap is fine, the car passes emissions inspections and after clearing the code the light comes back on immediately upon starting the car.

My mechanic speculates that perhaps a rodent chewed on a wire, but before I start trying to chase that down, does anyone else have any better guesses than a chewed wire?

 

Well, this is a momentous moment, first post in eleven years of membership It seems most all of the failing gas caps look fine. A Slant replacement cap seems to be a popular brand. It also may take some driving cycles to clear the code.

 

What is the code number??????


On the gas cap isssue, the car checks the purge valve, the canistor solenid, and the tank pressure readings twice every start up. Depending on which of these has the problem, it going to throw a specific code. So the gas cap concept is that the cap is not sealing correctly, and it will be the tank pressure reading that will be off to throw that specific code.

The glitch, when you start the car, the canistor solenoid is closes to seal the tank off that way, the purge vavle is kept closed for a short time to keep the tank sealed off that way, and this causes the differential reading on the tank pressure sensor that allow the two test to pass. Once the tests pass, then the tank is percantge relieved via the purge valve.

So again, could be the canister solenoid valve in the rear that has a problem (burnt out, or one of the two wiring to it has a broken wire/problem in the C186 connector next to the battery), the purge valve in the engine bay at the front of the car that has a problem or broken wire, pressure sensor has a problem, or could be the lines to all the above having leaks isntead.

So to sum it up, the trouble code that is in memory will tell you which part is having a problem, it can be pulled from the car to check it, as well as the wiring check to make sure one of them is not broken or one of the venting lines having a crack instead.

 

The OBD2 system has codes for both small and large EVAP system leaks. They can indeed be caused by a loose, or failing gas cap.

But they can also be caused by a lot of other things. Failed vent valve, cracked evap hose, cannister....

Suggest you get the ACTUAL code you are fighting, and start by researching it on the Internet.

https://www.freeasestudyguides.com/e...eak-p0457.html

If a new gas cap doesn't fix the problem I suggest you take it to a qualified mechanic. Chasing evap leaks generally requires having a smoke machine, AND experience knowing where certain cars are mostly like to experience EVAP leaks. Otherwise you can end up throwing parts at it without the light going out.

 

Thanks for the suggestions so far. I am currently 3000 miles away from the car, out of the country on vacation. I will get the code(s) when I return next week. Also, sorry for the lack of participation in the forum. I honestly forgot that I was a member, and thought I'd have to go find a good Corvette forum to join in order to pose my question. I'll try to do better, but I'm much smarter at answering questions about electric guitars than I am about Corvettes.