What does a persistent P0456 code indicate for an F150?

F150
1

I have a 2015 F150 with a 3.5L Ecoboost engine, and I got a P0456 (Small Evap Leak) code two months ago. I cleaned the capless filler flap and cleared the code, but it came back. Then I replaced the purge control valve (BL3Z-9B325-C) on top of the engine. I cleared the code again, and it was fine for a few weeks, but now it’s back.

I did some more research this morning and found a video showing that the capless filler neck has two flaps: a larger outer flap and a smaller inner flap. The smaller flap should only open when you insert the gas pump nozzle because it compresses two tabs. It’s a safety feature to prevent gas theft.

I went outside to check mine, and I could push open the inner flap with my finger, but I couldn’t see any tabs. It was dark, so I didn’t have a good view.

On a 2015 F150, should you be able to push open that inner flap with just your finger? If not, that might be what’s causing my code.

5 Likes
2

I can’t comment on how the smaller flap works, but here’s what the service manual says:

P0456 - Evaporative Emission System Leak Detected (Very Small Leak)

Description: This code means a fuel vapor leak as small as 0.508 mm (0.020") has been found by the EVAP system test.

Possible Causes:

  • Very small holes or cuts in the fuel vapor hoses or tubes
  • Loose connections of hoses or tubes in the EVAP system
  • Leaking seals on EVAP system parts

What to Check:

  • Make sure the fuel filler cap is not missing and is in good condition (if your vehicle has one).
  • If you have a capless fuel tank, check that the filler pipe is sealed properly.
  • Remove and reinstall the supplemental fueling adapter five times in the capless filler pipe to clear any debris.
  • Look for loose or damaged vapor hoses.
  • Check the EVAP canister and its parts for any dirt or debris.
3

Thanks, Jesse. I really appreciate it!

I’ve looked over this truck pretty thoroughly over the years, and I don’t remember ever finding the supplemental fueling adapter (fuel funnel). My kid has a 2016 2.7L F150, and I’ll have him check that inner flap when he gets home from work. In the meantime, I think I’ll spray some WD40 on it to see if it’s just stuck from dirt.

4

There’s another valve by the gas tank, and it could be the charcoal cannister as well.

5

Just a note:

A very small leak won’t trigger a code right away after you clear it, which is why there’s a delay in getting the code.

You might need to use a hand vacuum pump to test different parts of the system and valves for leaks.

It would help to get a detailed photo of the system to see what parts are where.

Good luck!

6

Thanks, everyone!

Does anyone know if the emissions testing place will fail me for a pending code? I haven’t needed an emissions test in almost 20 years.

I do have a hand vacuum, so I’ll look for a diagram of the emissions system and start testing. There have been a few times before when a smoke machine would have really helped with my past vehicles, so I guess it’s time to finally buy one.

7

I think P0456 is related to a fuel vapor pressure leak test done with the engine off. The PCM runs a 45-minute test while the engine is off by closing the vent solenoid to seal the system. If the pressure doesn’t reach 0.7 inches of H2O, which is the passing level, the PCM will open the vent solenoid, release the pressure, and set the P0456 code.

8

Yes, in my experience, codes can’t just be “pending.” They need to be fully set, which will either mark them as ready or trigger a check engine light (CEL). You can check the monitor status with most OBD scanners, like Forscan.

This is to stop people from clearing codes for a P0420 catalytic converter issue and then going for an emissions test before the ECU has finished checking if the problem is still there.

In places like California, there are some specific rules based on the year of the vehicle. For example, a certain number of items can be not ready (like 1 or 2), but not all of them.