P0456 and gas cap loose warning
Thread Starter
Newbie
Joined: Jun 2025
Posts: 1
Likes: 0
C450
P0456 and gas cap loose warning
Hey guys.
new to this forum and Mercedes in general. Purchased my c450 two years ago at 32k miles. Its been a nice ride so far. however, within the past few months I’ve gotten random gas cap loose warnings on my dash. I would pull over, turn car off, and make sure it’s sealed and then it would go away. Did this about 3-4x sporadically. As time went on — CEL came on randomly one day (P0456). That same day I stopped and got gas and the bruv didn’t want to start on the first get go. More and more loose gas cap warnings kept coming and tbh the cap rubber looked fine to me, but I went ahead and purchased one from the dealership and crossed my fingers. I cleared the code same time I switched the cap …. But it came back!! Additionally every time I get gas.. he doesn’t want to start on the first time. But it will on the second try (weak and lengthy start up). So now I am here hoping to see if anyone has any advice for me on where to get started.
im pretty savvy with working on cars, usually with guidance from a YouTube video, etc. if anyone has any idea of common EVAP system failures in w205s please let me know (college student and not really trying to pay for something I could possibly try on my own). The car is currently at 46k miles and I use 93 only since purchased. Also, I don’t really smell gas or anything from anywhere — I just find it really weird how the car only struggles to turn on when I get gas + it keeps showing loose gas cap warnings.
thank you to anyone who reads this message!! Any advice appreciated.
new to this forum and Mercedes in general. Purchased my c450 two years ago at 32k miles. Its been a nice ride so far. however, within the past few months I’ve gotten random gas cap loose warnings on my dash. I would pull over, turn car off, and make sure it’s sealed and then it would go away. Did this about 3-4x sporadically. As time went on — CEL came on randomly one day (P0456). That same day I stopped and got gas and the bruv didn’t want to start on the first get go. More and more loose gas cap warnings kept coming and tbh the cap rubber looked fine to me, but I went ahead and purchased one from the dealership and crossed my fingers. I cleared the code same time I switched the cap …. But it came back!! Additionally every time I get gas.. he doesn’t want to start on the first time. But it will on the second try (weak and lengthy start up). So now I am here hoping to see if anyone has any advice for me on where to get started.
im pretty savvy with working on cars, usually with guidance from a YouTube video, etc. if anyone has any idea of common EVAP system failures in w205s please let me know (college student and not really trying to pay for something I could possibly try on my own). The car is currently at 46k miles and I use 93 only since purchased. Also, I don’t really smell gas or anything from anywhere — I just find it really weird how the car only struggles to turn on when I get gas + it keeps showing loose gas cap warnings.
thank you to anyone who reads this message!! Any advice appreciated.
Super Member
Joined: Aug 2003
Posts: 772
Likes: 81
From: Bayarea, California
2003 C320 coupe/c450 in Feb 2016
did you fixed the problem? i also have C450 but with 171k miles. got engine light on, took it to dealer, they performed ME Control Unit Software updates. a few days later the GAS CAP LOOSE message popped up again and engine light on, the engine light wont go off for 3 days now. i just filled up gas, the car start up with no problem. i going to replace the gas cap to see if it fixes the problem.
