P0456 won't clear! - not the gas cap

[Htfan]

Just before all this covid19 shutdown started, I had my JLU at the dealership to fix the ESS and replace the aux battery. About a day or two later I get a P0456 check engine light.

I've turned and "clicked" the gas cap several times. It's not loose. I've tried clearing the code through OBDII and a 12 +8 Cable, but no luck. It's been 2 weeks.

Any thoughts? I have a good dealership for service, but don't like to go unless absolutely necessary. And right now they're probably shut down anyway.

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[dsgrey]

Just before all this covid19 shutdown started, I had my JLU at the dealership to fix the ESS and replace the aux battery. About a day or two later I get a P0456 check engine light.

I've turned and "clicked" the gas cap several times. It's not loose. I've tried clearing the code through OBDII and a 12 +8 Cable, but no luck. It's been 2 weeks.

Any thoughts? I have a good dealership for service, but don't like to go unless absolutely necessary. And right now they're probably shut down anyway.

What engine? TSB 18-088-18 is specific to only the 2018 with a 2.0 giving an erroneous P0456 code. I see you have a 2018 but not sure which engine.

 

[Htfan]

What engine? TSB 18-088-18 is specific to only the 2018 with a 2.0 giving an erroneous P0456 code. I see you have a 2018 but not sure which engine.

Right, I should have mentioned that I have a 3.6.

I've seen the threads on the 2.0 TSB.

 

[Aidencaster]

I'm not a mechanic by any means. I once got this code on my old 1500 dodge. It ended up being the fill nozel gasket. To think about it then the code came up after I filled up with a gas nozzle that didnt fit correctly and I had to jam it inside and then read in it to get it back out. Weird I know.

One site I searched just now gave me a multitude of options for this issue since it states it is a universal code. It will have something to do with your evap system.
https://www.700r4transmissionhq.com/p0456-jeep-wrangler/

• Evap System Hose– The hose that carries the fuel vapor from the fuel tank to the intake manifold can begin to leak. This will cause the P0456 code. Look for either a tear or hole in it. This is one of the most common issues that causes the code.
• Vapor Canister Purge Valve– One of the most common causes of the P0456 code is the vapor canister purge valve. It’s really easy to replace. There are a few clips that you need to find and remove.
• Fuel Tank Sending Unit– It is possible for the gasket that attaches the fuel sending unit to the gas tank to go bad. This can reduce tank pressure and throw the code.
• Fuel Cap– A bad fuel cap can cause the code to be thrown for sure. Often, you’ll get a message informing you that the fuel cap is off even when it is on. If you are getting that message, plus a P0456, it may save you a ton of time and money to replace the fuel cap and see if it goes away.
• Fuel Filler Neck– There is often a gasket where the fuel filler neck connects with the gas tank. This gasket can dry out, especially with vehicles that spend their time in dry climates. When it dries out, the fuel tank can’t hold pressure anymore.

 

[Htfan]

I'm not a mechanic by any means. I once got this code on my old 1500 dodge. It ended up being the fill nozel gasket. To think about it then the code came up after I filled up with a gas nozzle that didnt fit correctly and I had to jam it inside and then read in it to get it back out. Weird I know.

One site I searched just now gave me a multitude of options for this issue since it states it is a universal code. It will have something to do with your evap system.
https://www.700r4transmissionhq.com/p0456-jeep-wrangler/

• Evap System Hose– The hose that carries the fuel vapor from the fuel tank to the intake manifold can begin to leak. This will cause the P0456 code. Look for either a tear or hole in it. This is one of the most common issues that causes the code.
• Vapor Canister Purge Valve– One of the most common causes of the P0456 code is the vapor canister purge valve. It’s really easy to replace. There are a few clips that you need to find and remove.
• Fuel Tank Sending Unit– It is possible for the gasket that attaches the fuel sending unit to the gas tank to go bad. This can reduce tank pressure and throw the code.
• Fuel Cap– A bad fuel cap can cause the code to be thrown for sure. Often, you’ll get a message informing you that the fuel cap is off even when it is on. If you are getting that message, plus a P0456, it may save you a ton of time and money to replace the fuel cap and see if it goes away.
• Fuel Filler Neck– There is often a gasket where the fuel filler neck connects with the gas tank. This gasket can dry out, especially with vehicles that spend their time in dry climates. When it dries out, the fuel tank can’t hold pressure anymore.

Great info! Thank you for this. I'll start the investigation.

 

[#4Jeep 1st Wrangler]

Car dealerships are still considered " essential businesses".. They will be open even when states have shut downs. Emission codes are not easy to figure out....
You stated that the battery was replaced recently.. Probably left something disconnected? Damaged?... Several items need to be moved/ dis-connected when replacing battery....
If you feel like a detective.. Start looking around under the hood around the batteries... Might get lucky

 

[Htfan]

Car dealerships are still considered " essential businesses".. They will be open even when states have shut downs. Emission codes are not easy to figure out....
You stated that the battery was replaced recently.. Probably left something disconnected? Damaged?... Several items need to be moved/ dis-connected when replacing battery....
If you feel like a detective.. Start looking around under the hood around the batteries... Might get lucky

Appreciate your input. I do suspect something happened during the aux battery replacement so I mentioned it. I've already been poking around the battery and fuse box, but nothing is obvious. I'll try the dealership tomorrow. Didn't realize they were considered essential.

 

[jeepoch]

Jeff,

Hello, I used to be a Chrysler Powertrain Software Engineer who worked on (actually coded) OBDII federally mandated emission control systems, including Evaporative Fuel monitors. Unfortunately, that was quite a few years back. While the fault codes have likely remained the same, the mechanism in which to perform the tests have most probably changed since the 2002 - 2010 MY programs I was involved with.

Essentially, back then we had a purge pump that would slightly depressurize the fuel tank and lines. The controller would then read air pressure sensors looking for leaks, for a return to current ambient (atmospheric) air pressure, as also determined and compared to the Manifold Air Pressure (MAP) sensor, at engine off. This monitor would only run however after something called a 'good-trip' was achieved. This would be a certain amount of engine run-time, engine temperatue between certain calibrated thresholds, above a mimimum amount of fuel, under a calibrated altitude (ambient air pressure) and a minimum amount of miles driven over a specified speed typically around about 19 mph. At the very next ignition off event, this monitor would run. It would only require about 10 seconds to pass (no leak) or less depending on whether a course or fine leak was detected.

These sensors basically indicate air pressue inside the tank after depressurization. If the supposedly closed system remains closed over that calibrated time period then no problem. If the pressure increased to atmosphere within that time, then an error count would be incremented.

If this error count was above zero but below a fault value, the good-trip parameters would be modified depending on whether a course or fine leak was determined. If the same test subsequently passed this error count would decrement (but never below zero). If this subsequent test did not pass, the error count would continue to eventually increment to the fault value. At this point the appropriate P code would be thrown for the type of leak detected.

So it certainly sounds like you have somehow either acquired a leak or the controller detected an improper impedence (open or short) of the involved sensors or circuit wiring. So not only do you need to inspect your fuel system and hoses but also the electrical sensor circuit (and any corresonding fuses).

Sorry I moved to Colorado and no longer work in the automotive industry. I'm still developing software products, but not Engine Controllers. Colorado was just too much of a pull to remain in Auburn Hills, MI. But honestly that was one really fun job and I do sometimes miss it.

Things may have changed a little since then. For instance they may have thrifted away the pump and instead are now using engine manifold vacuum, but the concept should be the same. If I had access to current JL circiut schematics I could help you more readily, but alas no such luck. Still I hope this helps in some small way.

Good Luck.
Jay

 

[Htfan]

Jeff,

Hello, I used to be a Chrysler Powertrain Software Engineer who worked on (actually coded) OBDII federally mandated emission control systems, including Evaporative Fuel monitors. Unfortunately, that was quite a few years back. While the fault codes have likely remained the same, the mechanism in which to perform the tests have most probably changed since the 2002 - 2010 MY programs I was involved with.

Essentially, back then we had a purge pump that would slightly depressurize the fuel tank and lines. The controller would then read air pressure sensors looking for leaks, for a return to current ambient (atmospheric) air pressure, as also determined and compared to the Manifold Air Pressure (MAP) sensor, at engine off. This monitor would only run however after something called a 'good-trip' was achieved. This would be a certain amount of engine run-time, engine temperatue between certain calibrated thresholds, above a mimimum amount of fuel, under a calibrated altitude (ambient air pressure) and a minimum amount of miles driven over a specified speed typically around about 19 mph. At the very next ignition off event, this monitor would run. It would only require about 10 seconds to pass (no leak) or less depending on whether a course or fine leak was detected.

These sensors basically indicate air pressue inside the tank after depressurization. If the supposedly closed system remains closed over that calibrated time period then no problem. If the pressure increased to atmosphere within that time, then an error count would be incremented.

If this error count was above zero but below a fault value, the good-trip parameters would be modified depending on whether a course or fine leak was determined. If the same test subsequently passed this error count would decrement (but never below zero). If this subsequent test did not pass, the error count would continue to eventually increment to the fault value. At this point the appropriate P code would be thrown for the type of leak detected.

So it certainly sounds like you have somehow either acquired a leak or the controller detected an improper impedence (open or short) of the involved sensors or circuit wiring. So not only do you need to inspect your fuel system and hoses but also the electrical sensor circuit (and any corresonding fuses).

Sorry I moved to Colorado and no longer work in the automotive industry. I'm still developing software products, but not Engine Controllers. Colorado was just too much of a pull to remain in Auburn Hills, MI. But honestly that was one really fun job and I do sometimes miss it.

Things may have changed a little since then. For instance they may have thrifted away the pump and instead are now using engine manifold vacuum, but the concept should be the same. If I had access to current JL circiut schematics I could help you more readily, but alas no such luck. Still I hope this helps in some small way.

Good Luck.
Jay

Thank you Jay. Wow!

This is very good information. I really suspect that something caused an open/short in the sensor wiring you mentioned when my Aux ESS battery was replaced by the dealership. I'll contact them this week.

 

[JeepCares]

Just before all this covid19 shutdown started, I had my JLU at the dealership to fix the ESS and replace the aux battery. About a day or two later I get a P0456 check engine light.

I've turned and "clicked" the gas cap several times. It's not loose. I've tried clearing the code through OBDII and a 12 +8 Cable, but no luck. It's been 2 weeks.

Any thoughts? I have a good dealership for service, but don't like to go unless absolutely necessary. And right now they're probably shut down anyway.

@Htfan,
We are happy to know that you are bringing this to the attention of your dealer. Please know that our team is always available for additional assistance during your servicing visit. Feel free to private message us anytime.
Kathryn
JeepCares

 

[JLYaker]

Just before all this covid19 shutdown started, I had my JLU at the dealership to fix the ESS and replace the aux battery. About a day or two later I get a P0456 check engine light.

I've turned and "clicked" the gas cap several times. It's not loose. I've tried clearing the code through OBDII and a 12 +8 Cable, but no luck. It's been 2 weeks.

Any thoughts? I have a good dealership for service, but don't like to go unless absolutely necessary. And right now they're probably shut down anyway.

I had the same issue. I replaced both batteries and a few days later the check engine light came on. I went to AutoZone to check the trouble code and got PO456. They sold me a replacement canister purge valve but I haven't been able to find where it goes yet. Did you ever solve your problem?

 

[Htfan]

I had the same issue. I replaced both batteries and a few days later the check engine light came on. I went to AutoZone to check the trouble code and got PO456. They sold me a replacement canister purge valve but I haven't been able to find where it goes yet. Did you ever solve your problem?

My p0456 code has been resolved, however I don't have much helpful info to provide. My dealership wanted me to bring it in, but because of the hassle - level of service visits, I was in no rush.

The problem code cleared itself after I completed some unrelated battery load testing. Since I pulled the main battery and disconnected the aux battery to test, the Jeep was without 12v for several minutes. After reinstalling both batteries, the code has never returned after a couple months of driving it.

 

[Sol]

Today’s trip to the dealer service department for a Check Engine Light (2018 JLU w/3.6) turned out to be for a P0456 code. Summary:
*Noted because it was the only other thing out of the ordinary, a Stop/Start Not Ready message accompanied the CEL - turns out Stop/Start is disabled with an active CEL
*Evap system passed leak tests
*PCM update addresses nuisance P0456 code - reprogrammed to 68440959AC

 

[jgdiablo]

I had P0456 a few days ago and after a visit to the dealer, they had to replace the ESIM and updated the PCM to the latest firmware. Fixed!

 

[Htfan]

I just visited the dealership for a jeep wave oil change and they updated the PCM according to the TSB also.

It's also been said this PCM update will correct the starting issues with a dead or low voltage aux/ess battery. It now works similar to the new model years.

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