Fuel Pump running with car off

So my fuel pump cycles even when the car is off. If I park the car the fuel pump may cycle on/off (like it's priming) moments later or many minutes later, but either way it will continue to cycle at that the same intervals; it seems to matter how much fuel is in the tank. I have the P1456 code, but I have searched and no where does anyone mention that their fuel pump is cycling like mine. I hope this makes it easier to figure out and I just don't know fuel systems enough so I need help.

I tend to think the only reason the fuel pump would cycle is because the pressure sensor is sending a lack of pressure message to the ECU...is this correct? And the reason the fuel pump cycles at different intervals is because of the pressure/weight of the fuel in the tank being more or less depending on how much gas is in it. Possible or not?

I have changed my fuel cap, but that's it. The car runs fine and I'm not too worried or panicked about it because it has done this for the last 30K miles or so, but it's something I should fix now and prevent having to deal with a non-running car.

Car is a 99' LX 4-door auto. Has 225K miles. Using regular unleaded.

Fuel pump should get power only when key on, sounds like yours gets it all the time, also fuel pump should be on or off, not cycle.

Find out voltage issue.

Are you sure your Evap Canister isn't just purging itself ? Mine usually does it every few minutes for an hour or so after the car is off ..

I think in most cars you turn the key one click forward and the fuel pump primes, that is what this sounds like. But in my case it happens without the key in the ignition. Sometimes it happens very infrequently, like every hour or so, and sometimes shorter like every 10 minutes. I don't know for sure because I'm not always checking to see when the fuel pump is running after I get out of the car.

I realize this may not be simple, I was just hoping the things were connected so I could narrow it down.

Does the ECU receive fuel pressure data (not just O2 readings), and could it cause the fuel pump to run when the car is off?