Need help with p0451 code

[Builtbyageek]

"Evaporative Emission System Pressure Sensor/Switch"

I've been chasing this code for awhile. First thinking it was the purge valve, then the evap canister. Replaced both with no change. I've read stories of people having issues when completely filling up the gas tank, like it stumbles and it's usually the purge valve but my has been running great.

Is there a pressure sensor on or near the gas tank? I know there's one on the fuel rail but can't find a diagram that shows one near the fuel tank. I'm assuming it's on a line off the canister somewhere?

 

[JackInaboxx]

Car just threw that same code to me again, two years after changing the purge valve. Debating if I should replace it again or just clear the codes every two weeks as it doesn't really affect the car at all (no stumbling at all).

Doesn't seem like a fuel pressure issue to me as there were no fuel pressure codes at all (P0087 Fuel rail pressure/system pressure too low and P008a Low Fuel pressure).

 

[Builtbyageek]

Yeah it's not a fuel rail pressure issue, that's for sure. I've seen on another forum that someone had the same code, and the dealer replaced the "gas tank pressure sensor". I didn't see a pressure sensor on the top of the fuel tank/pump itself, but I thought maybe it could be part of the lines in the back near the evap canister. I recall a few connectors last time I was underneath the car.

I've just been driving the car like that for 2 years. I stopped clearing the code. The light does eventually go out by itself, and then it comes back. I'd just like to find the issue though. I may try slicing in another purge valve instead of changing the whole harness and see what happens.

 

[JackInaboxx]

Yeah it's not a fuel rail pressure issue, that's for sure. I've seen on another forum that someone had the same code, and the dealer replaced the "gas tank pressure sensor". I didn't see a pressure sensor on the top of the fuel tank/pump itself, but I thought maybe it could be part of the lines in the back near the evap canister. I recall a few connectors last time I was underneath the car.

I've just been driving the car like that for 2 years. I stopped clearing the code. The light does eventually go out by itself, and then it comes back. I'd just like to find the issue though. I may try slicing in another purge valve instead of changing the whole harness and see what happens.

Yeah I saw that comment too, been looking all over to figure out where this gas tank sensor would be - the thing is too that if that was the case we would get weird dash gas level behaviour, but everything is fine on my end. I have a 2014, and I have the bad habit of filling the tank up to the top. Check engine light came off as soon as tank gas level went down under 3/4.

I have a leftover harness too that I need to convert into one that can accomodate quick changing the purge valve. Might just be that changing the purge valve every two years is the consequence of Ford engineering...

 

[JackInaboxx]

Just as an update: replaced the evap harness with another one I have laying around. Clamped some silicone tubing hose (I/D 3/8"), along with a Dorman 994038 purge valve after removing the old plastic tubing. P0451 when cleared will disappear for a day or two then reappear. Again - it'll reappear faster when my tank is full. Will double check if everything is properly done under the hood, but this might call for the replacement of the charcoal canister, and probably throwing in another purge valve.

That or maybe it's an issue with the fuel filling neck. Or maybe I'll just keep the CE light on and check every month to see if it's the only code.

 

[Builtbyageek]

Changing the canister didn't change anything for me sadly. I've been living with the CEL on, but it'll go off by itself and then reappear eventually. I haven't been able to find a pattern for when it goes out by itself or when it appears. I also fill up until it clicks usually, so maybe I'll try just giving it a bit of gas while the light is currently off and see how long it takes for it to come back on.