I sort of had this problem. It would go on and off, even with different gas caps. But then i had bigger problems with the gauge system in the tank and had it replaced. after that no gas cap warnings.

 

Well, it's back. And it brought a little friend this time. CEL P0457. This is with the new gascap. I know it could be a number of things but what should I check first?

 

I had the gASCAP code as well on my 08 Dakota 4.7L. It was on for about 2 days and then turned into a check engine light. I cycled the key 3 times to read the codes and found P0455, P0456 and P0457. I took it in to the dealer to get that looked at along with some front end work while it is still under warranty. The day before it went in it started saying "Oil Change Due" or something like that but since I still have 1000km before my next scheduled oil change I cleared it as it says in the manual. Amazingly it also cleared the check engine light. Anyway it went in for service and they did the front end work and replaced the gas cap. I figured they would have checked the codes, addressed, and cleared them but I was curius so when I got home I cycled the key to check the codes and I still had P0455 and P0456. I stopped by my buddies place for a beer and had him clear the codes. And then a day later the check engine light came back on and now I only have P0455. So I'm gonna call the dealer tomorrow and get them to fix it. I'm still covered under warranty until April.

 

There's a good chance you may have a vac line for the evap system that is disconnected or cracked. Most likely just cracked because a disconnected line would most likely give you a code for "large leak". I had this issue with a neon and narrowed it down to a line on top of the tank that cracked. The purge system sensed the pressure problem in the tank and threw a code.

Have someone do a "smoke test" on the system. It's a good way to find a leak like this.

 

Jeff,

Have you been able to bring your Dakota back to the dealer? What was the outcome? If you have any inquiries or concerns feel free to PM me.