Evaporative control system leak, codes P0456 and P0455

Hi good morning,

So you are getting both codes at the same time? Usually I would expect to see one or the other so that interesting to me. Anyway, the P0455 is the more important one to deal with. Let me know what steps you have take so far. For instance have you inspected the fuel cap to see if it is sealing properly. That is the number one cause for these types of codes. But there are a few other possibilities if that is not the problem.

Typically what I do is run a "Smoke Test" on the system where I plug a smoke machine into one of the lines in the system and watch to see where the smoke gets let out! Its by far the easiest way to determine where the leak is.

As far as running new lines, you could do that if the prospect of lowering the tank is not in the cards for you. But in my experience, the lines are usually not the problem, most times I find that the plastic fittings dry rot, get brittle and crack. If you do find that the lines are the issue, make certain that the hose you use is rated to use on fuel systems or else it will degrade over a period of time.

Also I wouldn't recommend the flex seal for a fix.

Lets start with what you have done so far to diagnose your problem.

To add to the above, if by rerouting the lines you mean to bypass the lines to the tank and create a loop for the EVAP system, that will not work as the system is calibrated to test the EVAP system with the tank inline. It knows that with the fuel tank in place and it closes the vent and opens the purge vale that it should take X number of seconds with the fuel at level R to pull the tank to the test vacuum point. Then it should take Y seconds when it seals the purge valve off for the vacuum in the system to lower and when it opens the vent valve again it should take Z seconds for the tank to return to atmospheric pressure. If you were to put a line between the purge valve and the vent lines the volume will be much lower and it will now set other EVAP codes because of that.

As for the flex seal, while the straw would likely work if it were large enough, if you are thinking of using it to seal the EVAP leak, FS is not rated for gasoline and will dissolve rapidly in gas or fuel vapor and likely cause more issues depending on where it ends up.

There is no perfect but unless the system is working as designed it will set EVAP codes. Worse, if you were to block off the system at the tank or lines you will discover you cannot ad fuel to the tank and that the engine will start having problems because of the way the EVAP system operates to purge the tank, which will set other codes. Not trying to sound like a bad guy but the system isn't going to like being bypassed or altered.