"Intermittent" P0456 code

[asone]

I read Integra Emissions System Problem thread, but mine is a bit different.

I have a 2026 Type S that I picked up in late September 2025. Since mid December, it started to throw P0456 "intermittently". First time was on 12/11/25. Second time was on 1/11/26. The third time was on 2/11/26. It's weird that all 3 times happened on the 11th of the month.

Since this happened 3 times, I took the car to the dealer. They smoke tested but it was fine. So, they just cleared the code and that was it. No fix was made. Because nothing was done, I'm suspecting that this will happen again. I do wait well over 10 seconds before removing the gas nozzle after pumping the gas. I did try opening and closing both the outer flap and the inner flap a several times, but that didn't help.

Below is exact words on the paperwork.

Customer's concern of customer states vehicle will no longer make popping noise from exhaust and pulled DTC for P0456 at this time. Checked for service bulletins, service messages, recalls and service history. Road tested. Performed a visual inspection. Performed a diagnostic scan using the I-HDS and found DTC(S) P0456 in history. Performed evap test with smoke machine and no leaks found. Performed exhaust valve test and everything working as should. Cleared pending DTC. Inspection and diagnostics found no failed or defective components. No part replacement or repairs were made at this time. Performed test drive again after clearing DTC now vehicle will make popping noise. DTC history was a intermittent issue due to no leaks found on vehicle.

Did this happen to anyone? Was anything eventually got fixed?

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[ChromaPop]

I have a feeling that cannot be a coincidence that the code was thrown three times on the 11th of the month. The odds of that are like 27,000 to 1. I am curious if when you brought it to the dealer there was a software upgrade for the infotainment system and the engine check system? It sounds to me like merely a software error.

 

[asone]

I have a feeling that cannot be a coincidence that the code was thrown three times on the 11th of the month. The odds of that are like 27,000 to 1. I am curious if when you brought it to the dealer there was a software upgrade for the infotainment system and the engine check system? It sounds to me like merely a software error.

I updated my original post with what the tech said on the paperwork. It doesn't sound like he did any software upgrade during this visit. But it sure sounds like a software error because their diagnosis found no issues.

 

[SlippyFist]

are there even software updates for this car? i got mine in october 2023 and i was at the dealership earlier today to replace my expansion tank and i specifically asked them if there were any software or ECU updates available and he said no.

 

[asone]

Update. After the dealer cleared the code, I didn't get it for over 8 months and 4500 miles. The code came back yesterday, 10/30.

 

[UWU-mancer]

Update. After the dealer cleared the code, I didn't get it for over 8 months and 4500 miles. The code came back yesterday, 10/30.

Well damn. That sucks man. Time to go to the dealer again. If they ever figure it out plz let us know? I’m genuinely curious.

 

[FredS2000]

Intermittent evap very small leak codes suck. This is a leak of .020" or less. They are very difficult to find, even with smoke.

Here's what the car goes through to determine EVAP system integrity:

EONV test
The EONV test detects a small leak in the evaporative emission (EVAP) system by evaluating the changes in pressure that occur in the fuel system. The monitor is divided into two phases.
Phase 1
Phase 1 is executed while the temperature is still rising. A rise in temperature will lead to an increase in pressure in a tight fuel system. Between phase 1 and phase 2, the EVAP canister vent shut valve opens for a calibrated amount of time bleeding off any residual pressure.
Phase 2
Phase 2 is executed only when the pressure built in phase 1 does not reach levels that are typical of a tight fuel system. Phase 2 monitors the vacuum built when the fuel temperature is decreasing. Little or no vacuum is built if there is leakage in the system. For a leak free system, the vacuum build will reach a threshold that is determined by the ambient temperature and the fuel tank level.
The cases below are all possible fuel tank pressure characteristics.

	Case A: The pressure of a leak free system reaches the calibrated target differential pressure. The diagnostic is immediately terminated (no phase 2) when this calibrated threshold for a leak free system is achieved.
	Case B: The tank pressure does not reach the target pressure but a maximum differential pressure has been observed. The diagnosis will continue by opening the EVAP canister vent shut valve.
	Case C: A vacuum build is recognized when the pressure falls below a calibrated threshold for a calibrated time. In this case, the diagnosis will continue with phase 2 without the re-opening and closing of the EVAP canister vent shut valve.
	Case D: If the tank pressure remains within a calibrated window around barometric pressure for a certain time, the EVAP canister vent shut valve will be opened.
	Case E: The tank pressure gradually increases and does not reach the target pressure when phase 1 exceeds the maximum allowable run-time. The diagnosis will then proceed with the opening of the EVAP canister vent shut valve.
	Case F: After Phase 1 is complete, if the pressure reaches an upper limit, then further pressure is relieved by opening the EVAP canister vent shut valve for a calibrated amount of time. Opening and closing can be repeated up to a calibrated number of times within the maximum allowable calibrated run-time.
	Case G: The tank pressure remains close to ambient pressure within a calibrated window for a calibrated time in phase 2.
	Case H: The integrity of the system cannot be determined when the diagnostic exceeds the maximum allowable run-time.
	Case I: The tank pressure reaches a lower threshold and rises more than a calibrated value within the maximum allowable run-time. This confirms a minimum differential pressure had been achieved.
	Case J: The tank pressure (vacuum) reaches the possible minimal differential pressure in phase 2 within the maximum allowable run-time.

If the difference between the maximum differential pressure obtained in phase 1 and the minimum differential pressure obtained in phase 2 is less than the calibrated threshold, an EVAP system very small leak (P0456) will be detected.

Monitor Execution, Sequence, Duration, DTC Type

Execution​ Once per driving cycle​ Sequence​ None​ Duration​ 0.5 seconds or more​ DTC Type​ Two drive cycles, MIL on​

Enable Conditions
Start of diagnosis

Condition​ Minimum​ Maximum​ Outside air temperature​ 32 °F (0 °C)​ 103.6 °F (39.8 °C)​ Initial engine coolant temperature [ECT Sensor 1]​ –​ 113 °F (45 °C)​ Difference between initial engine coolant temperature and outside air temperature​ –​ 27 °F (15 °C)​ Barometric pressure [Baro Sensor]​ 74 kPa (555 mmHg, 21.9 inHg)​ –​ Other​ EVAP canister vent shut valve is not closed for EONV​

 

[FredS2000]

And more:

Operation conditions Condition​ Minimum​ Maximum​ Elapsed time after starting the engine​ 10 minutes​ –​ Elapsed time after the vehicle is turned to the OFF (LOCK) mode​ 20 seconds​ –​ Distance travelled​ 4 miles (5 km)​ –​ 12 volt battery voltage [Battery]​ 10.7 V​ –​ Fuel level​ 0.25 L (0.066 US gal)​ 40.75 L (10.764 US gal)​ Other​ Smallest leak not detected​ No refueling​ Diagnosis pressure phase (phase 1) Condition​ ​ Other​ EVAP canister vent shut valve is closed for EONV​ Cases A, B, or C occurs​ Case A: Pressure threshold is reached Condition​ Minimum​ Maximum​ Fuel tank pressure​ 0.5 kPa (4 mmHg, 0.15 inHg) - 1.800049 kPa (13.50145 mmHg, 0.5315545 inHg)*​ –​ *: Depends on fuel level​ Case B: Maximum pressure is detected Condition​ Minimum​ Maximum​ Fuel tank pressure​ 0 kPa (0 mmHg, 0 inHg)​ –​ Fuel tank pressure peak*​ 0.01 kPa (0.1 mmHg, 0.003 inHg)​ –​ *: For at least 50 seconds​ Case C: Vacuum builds Condition​ Minimum​ Maximum​ Fuel tank pressure*​ –​ -0.125 kPa (-0.93 mmHg, -0.0369 inHg)​ *: For at least 25 seconds​ Diagnosis vacuum phase (phase 2) Condition​ ​ Other​ Vacuum phase is activated for EONV​ EVAP canister vent shut valve is not closed for EONV​ Cases F, G, H, I, J, or D occurs​ Case F: Pressure build Condition​ Minimum​ Maximum​ Fuel tank pressure​ 0.063 kPa (0.48 mmHg, 0.0186 inHg)​ –​ Other​ Diagnosis is not rejected​ Case G: Stabilization at zero Condition​ Minimum​ Maximum​ Absolute fuel tank pressure*​ –​ 0.063 kPa (0.47 mmHg, 0.0186 inHg)​ Other​ Diagnosis is not rejected​ *: For at least 15 minutes​ Case H: Diagnosis timeout Condition​ Minimum​ Maximum​ Elapsed time after the vehicle is turned to the OFF (LOCK) mode​ 45 minutes​ –​ Other​ Diagnosis is not rejected​ Case I: Vacuum peaks Condition​ Minimum​ Maximum​ Fuel tank pressure*​ –​ -0.125 kPa (-0.93 mmHg, -0.0369 inHg)​ Fuel tank pressure (vacuum) peak*​ 0.01 kPa (0.1 mmHg, 0.003 inHg)​ –​ Other​ Diagnosis is not rejected​ *: For at least 50 seconds​ Case J: Vacuum threshold is reached Condition​ Minimum​ Maximum​ Fuel tank pressure​ 0.5 kPa (4 mmHg, 0.15 inHg) - 1.800049 kPa (13.50145 mmHg, 0.5315545 inHg)*​ –​ Other​ Diagnosis is not rejected​ *: Depends on fuel level.​ Case D: Vacuum builds Condition​ Minimum​ Maximum​ Absolute fuel tank pressure*​ –​ 0.063 kPa (0.47 mmHg, 0.0186 inHg)​ *: For at least 15 minutes​ Diagnosis canister close valve is open (between phase 1 and phase 2) Condition​ ​ Other​ Pressure phase is not activated for EONV*​ Vacuum phase is not activated for EONV*​ EVAP canister vent shut valve is not opened for EONV*​ *: For at least 6 minutes 40 seconds​ Diagnosis vacuum phase (phase 2) Condition​ ​ Other​ Vacuum phase is activated for EONV​ Pressure phase is not activated for EONV​ EVAP canister vent shut valve is closed for EONV​ Cases F, G, H, I, J, or E occurs​ Case F: Pressure build Condition​ Minimum​ Maximum​ Fuel tank pressure​ 0.063 kPa (0.48 mmHg, 0.0186 inHg)​ –​ Other​ Diagnosis is not rejected​ Case G: Stabilization at zero Condition​ Minimum​ Maximum​ Absolute fuel tank pressure*​ –​ 0.063 kPa (0.47 mmHg, 0.0186 inHg)​ Other​ Diagnosis is not rejected​ *: For at least 15 minutes​ Case H: Diagnosis timeout Condition​ Minimum​ Maximum​ Elapsed time after the vehicle is turned to the OFF (LOCK) mode​ 45 minutes​ –​ Other​ Diagnosis is not rejected​ Case I: Vacuum peaks Condition​ Minimum​ Maximum​ Fuel tank pressure*​ –​ -0.125 kPa (-0.93 mmHg, -0.0369 inHg)​ Fuel tank pressure (vacuum) peak*​ 0.01 kPa (0.1 mmHg, 0.003 inHg)​ –​ Other​ Diagnosis is not rejected​ *: For at least 50 seconds​ Case J: Vacuum threshold is reached Condition​ Minimum​ Maximum​ Fuel tank pressure​ 0.5 kPa (4 mmHg, 0.15 inHg) - 1.800049 kPa (13.50145 mmHg, 0.5315545 inHg)*​ –​ Other​ Diagnosis is not rejected​ *: Depends on fuel level​ Case E: Pressure build timeout Condition​ Minimum​ Maximum​ Elapsed time after the vehicle is turned to the OFF (LOCK) mode​ 45 minutes​ –​ Malfunction Threshold The pressure difference for leak decision between overpressure and vacuum phase is less than 0.084961 kPa (0.63726 mmHg, 0.0250890 inHg) - 0.199951 kPa (1.49975 mmHg, 0.0590455 inHg)*. *: Depends on fuel level Possible Cause NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes. EVAP system very small leak Confirmation Procedure Operating Condition 1.​ Start the engine and drive the vehicle for at least 4 miles (5 km). 2.​ Turn the vehicle to the OFF (LOCK) mode and wait for a while. Avoid driving conditions that could lead to fuel slosh in the fuel tank. Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow. Diagnosis Details Conditions for setting the DTC When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle, the MIL comes on and a Confirmed DTC, the freeze data, and the on-board snapshot are stored. Conditions for clearing the DTC The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, the freeze data, and the on-board snapshot can be cleared with the scan tool clear command.

 

[Victorofhavoc]

I would dump that Honda manual jibber jabber into an Ai and devise a test plan you'd expect the dealer to follow.

Have you ever had this happen during warmer months? A tiny leak due to some debris in the flaps plus the temp swings through colder months could easily trip the temp/pressure based calculation it's doing. Its calcs are based on entirely sealed, perfect world systems with normal temp swings (keeping in mind the Midwest, IL included, sees non-normal temp swings several times per year) so a short 5mi drive during a weather event could trip it without a leak too.

 

[asone]

Thanks for the info all!

I purchased the car at the end of Sept '25. The code appeared 5 times between 12/11/25 and 2/13/26. I cleared it myself the first 4 times. The dealer cleared it the 5th time. Then no code until 10/30/26. So, the first 5 times were happening only during cold days. But the last one on 10/30/26 wasn't cold. About ~45F to ~55F. Also, the fuel level was anywhere between 20% and 80%.

Every morning, I drop my son off at school. It's 3.5 miles to get there and come back. Because of the congested drop off line, that 3.5 miles takes 15-20 minutes. The code never appeared during those drives. It only appears on my second drive of the day.

I had AI check this thread out and I explained what happened to my car, it says what FredS2000 says explains what happened to my car. But it says if P0456 is triggered twice in a row, it would trigger CEL. It also says if P0456 doesn't get triggered for a while, it would clear this code on its own. I'm not sure if those are true from my experience. Also, before it said that, it thought my CEL was on because of P0456. What AI says makes me think it's just saying whatever without actually knowing it.

I already cleared the last code. Next time it happens, I'll try leaving it for a week and see if it actually goes away on its own. If it doesn't, then I'll take it to the dealer. It's about the time to get an oil change too.

 

[asone]

Have you ever had this happen during warmer months? A tiny leak due to some debris in the flaps plus the temp swings through colder months could easily trip the temp/pressure based calculation it's doing. Its calcs are based on entirely sealed, perfect world systems with normal temp swings (keeping in mind the Midwest, IL included, sees non-normal temp swings several times per year) so a short 5mi drive during a weather event could trip it without a leak too.

I did some research and this actually looks like is a pattern. 5 out of 6 times I got the code, the temp change overnight were large. About 30F.

12/11/25. Only 13F drop.
12/14/15. 28F drop.
12/29/25. 32F drop.
1/11/26. 30F drop.
2/13/26. 30F rise.
10/30/26. 24F drop.

That, plus 3.5 mile short drives.

Only other days that had temp drop/rise of more than 25F were 12/19, 1/14, and 1/23. 12/19 was no school (already winter break). I'm pretty sure I didn't drive my car on 1/14 and 1/23. I remember I started to use my wife's EV because EV heats up instantly and was ideal for a short drive in the cold mornings. So, I've been getting P0456 on every large temp drop/rise days that I had 3.5 mile drive early in the morning, except 12/11/25. I don't know what triggered first one.

Very interesting.

 

[Victorofhavoc]

I did some research and this actually looks like is a pattern. 5 out of 6 times I got the code, the temp change overnight were large. About 30F.

12/11/25. Only 13F drop.
12/14/15. 28F drop.
12/29/25. 32F drop.
1/11/26. 30F drop.
2/13/26. 30F rise.
10/30/26. 24F drop.

That, plus 3.5 mile short drives.

Only other days that had temp drop/rise of more than 25F were 12/19, 1/14, and 1/23. 12/19 was no school (already winter break). I'm pretty sure I didn't drive my car on 1/14 and 1/23. I remember I started to use my wife's EV because EV heats up instantly and was ideal for a short drive in the cold mornings. So, I've been getting P0456 on every large temp drop/rise days that I had 3.5 mile drive early in the morning, except 12/11/25. I don't know what triggered first one.

Very interesting.

It needs right at 4mi drive to trip the calculation conditions I believe (I think that's in the Honda manual notes above actually).

So that could be it especially if you hit right at the 4mi mark where the car is warm and everything is warming up (fuel pump and all) as you suddenly turn it off and leave the tank exposed to frigid concrete under the car. In a perfect, sealed world, it shouldn't happen. But if there's just a tiny bit of gunk on the flaps or pressure valve, then some miniscule amount of evap could squeak by and with a temp change you trip it.

I'd still write up your own game plan and then go to the dealer and have the take next steps since you have a record. If they're not taking ownership, then you give them the plan and tel them what to do. If they don't, reach out to acura national and hopefully they assist.

Otherwise you could try and clean the flaps first. They're easy to get to and a funnel wrapped in a terry cloth can clean them up okay

 

[asone]

It needs right at 4mi drive to trip the calculation conditions I believe (I think that's in the Honda manual notes above actually).

So that could be it especially if you hit right at the 4mi mark where the car is warm and everything is warming up (fuel pump and all) as you suddenly turn it off and leave the tank exposed to frigid concrete under the car. In a perfect, sealed world, it shouldn't happen. But if there's just a tiny bit of gunk on the flaps or pressure valve, then some miniscule amount of evap could squeak by and with a temp change you trip it.

I'd still write up your own game plan and then go to the dealer and have the take next steps since you have a record. If they're not taking ownership, then you give them the plan and tel them what to do. If they don't, reach out to acura national and hopefully they assist.

Otherwise you could try and clean the flaps first. They're easy to get to and a funnel wrapped in a terry cloth can clean them up okay

It says 4 miles (5 km). 5 km is just over 3 miles. So, maybe they just say "4 miles" but it actually needs 3.1 miles (5 km). If you say 3 miles, then it's false, but 4 miles is true. My morning drop off is 3.5 miles. Shorter route is like 3.3 miles.

So, I probably have a several times a year of chances to get this code. I'll just keep bringing in every time it happens.

 

[jedi03]

Just went through this fun with a jeep...replaced the tank pressure sensor an found the charcoal canister sensor was the issue...the tank does different pressure tests depending on how much fuel you have in the tank...theres alot of Information that they should look at and when it triggers that will point to the culprit...a smoke test can help this too

 

[asone]

Just went through this fun with a jeep...replaced the tank pressure sensor an found the charcoal canister sensor was the issue...the tank does different pressure tests depending on how much fuel you have in the tank...theres alot of Information that they should look at and when it triggers that will point to the culprit...a smoke test can help this too

They did the smoke test too, but no leaks found. Mystery P0456.

Customer's concern of customer states vehicle will no longer make popping noise from exhaust and pulled DTC for P0456 at this time. Checked for service bulletins, service messages, recalls and service history. Road tested. Performed a visual inspection. Performed a diagnostic scan using the I-HDS and found DTC(S) P0456 in history. Performed evap test with smoke machine and no leaks found. Performed exhaust valve test and everything working as should. Cleared pending DTC. Inspection and diagnostics found no failed or defective components. No part replacement or repairs were made at this time. Performed test drive again after clearing DTC now vehicle will make popping noise. DTC history was a intermittent issue due to no leaks found on vehicle.

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