Ghennes13

Need answers for 2005 clk320 cel and fuel cap warning light. My car has 96,000 miles and has been great since I bought it last year. The only problem I'm having is out of nowhere a red warning light saying check gas cap comes on followed by CEL. I've already replaced the gas cap and had a evap smoke test showing no signs of leaks. The cel code is a po400. I then replaced the egr valve with a new one. I drove 50 miles and the check gas cap came on twice followed by the cel again!
What is going on here? I also checked the purge valve which is working properly. I'm guessing it could either be the charcoal canister valve, fuel neck, fuel sending unit? Is this a common issue with the clk? How can I fix this?? Thanks

Rudeney

I seem to recall some problems with the filler neck leaking.

Ghennes13

The filler neck itself? Or a hose connected to the filler neck? I took the car in today. The code is po455 and code 2274 . They want to charge $1400 to replace the charcoal canister, the fuel tank pressure sensor, and the purge line from the charcoal canister to the purge valve.

Rudeney

I poked around in SDS and it does have a full battery of automated tests for fuel tank pressure. It would come back with specific failures like this, so it does seem that this diagnosis might be accurate. Now, if I were doing this myself, I might actually do some further checks, like remove the hose and pressure test, or check the pressure sensor itself with an ohmmeter, etc. But shops don't do this - they just take the SDS instructions as gospel and swap parts.