Troubling p0456

9921 Views 10 Replies 6 Participants Last post by  guy65
Have a 2008 Ram 1500 with 5.7 L Hemi

Truck keeps throwing p0456...

There is a new mopar gas cap...
The truck was smoke tested...nothing
Was told that purge valve was ruled out.
I've also changed the EGR Valve twice now and the PCM last year because it was malfunctioning, i.e. burnt 4WD and likely the EGR too.

Something of interest, when the tank is filled, it almost always spits gas - even when filling on slowest setting.

I need to pass emissions and need to hopefully resolve this without lots of expensive exploration. Anyone have any thoughts or does this sound familiar?

Thank you.
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spitting gas was common on early jeep JK wranglers. there is a valve that needs to be replaced. might clear up you code.
Hi huntergreen,

Do you know the name of the valve?
Is it a difficult fix?

Thank you.
ncoppola- it's the evaporation valve. it sits usually directly at the fuel intake underneath. it's actually just a simple pipe with a ball in it. the gravity pulls the ball down and closes the pipe. if the airpressure increases in the tank, for example when you get gas, the air pushes the ball up and the air comes out there. the hose routs to the front to the active charcoal filter- there is another solenoid valve. one or both can be broken. that's usually the reason for spitting- the air can't go out fast enough and the backlash pushes the gas back out.

What I think about smoke don't wanna know.
guy65 - do you suppose it can also cause the p0456 code?

I'm not a tech, just a vehicle owner looking to troubleshoot.
As for the smoke test...I guess I won't ask...

Would a repair to this require dropping the tank? Thanks.
sometimes they either clog up or just stuck. There is also a similar cut off in the snorkel to the tank, which actually suppose to lock, when the tank is full, to prevent the gas from squirting out.
just a simple question- when you drive and stop. cut the vehicle off, like when you get gas. if you remove the gas cap- do you hear air flow? this is mostly a sign- but you would have to do it immediately after turning the vehicle off, because if it's too long, the pressure goes away slowly. usually there should be no pressure or vacuum.
The ball valve is hard to get to, because I think it's imbedded into the snorkel assembly.
What you can do- and I don't know how much technical equipment you have- if you have a air compressor, take a rag and the air handle and blow air in it, while you close the gap around the handle with the rag- but don't increase the pressure too fast. do it slow. this usually looses the ball and blows the dirt out. Another thing- check at the active charcoal filter, if there is a solenoid valve- pull the connector off and take 12 v and ground wires (best is if you would have a pigtail but if you're careful, you should be good). there should be only 2 pins because it's just a open/close valve. attach the + and tip the ground to the other pin and hear if it clicks. also- if you pull the hose off, yeah- little tricky- you might need 2 people for that- one blows in the tank, the other switches the valve and see, if the valve opens and closes and if air goes through and stops, when switched. that's pretty much all you can do. there is not more to the system.
And I be honest- I never done trouble shooting for that on a RAM, because I never had the issue. I can't tell you where the valve is, but it should be there- either directly at the fuel snorkel or right at the active charcoal filter. as far as logical positions.
If your error code is Gas Cap, that's where you got to check, when the gas cap is ok.

Here a link to some pictures- you should be able to find it with this:******************%25252Fforums%25252Ff170%25252F2004-dodge-ram-hemi-1500-vapor-canister-fuel-issues-11897.html&source=iu&pf=m&fir=9o8RAIDO6MCOgM%253A%252Cut9XAPPSnfiC9M%252C_&usg=__2lp3GyrVEqZvTzAAGy4CqT5yzkI%3D&ved=0ahUKEwjt8LC2sbnOAhVGbSYKHShnDCkQyjcIKQ&ei=i3KsV63_CsbamQGozrHIAg#imgdii=9o8RAIDO6MCOgM%3A%3B9o8RAIDO6MCOgM%3A%3BCHF_C6m3qYh2RM%3A&imgrc=9o8RAIDO6MCOgM%3A
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This for your 2008 Ram 1500 with the 5.7 Hemi. Other models/years may use a slightly different system.

Theory of Operation

The Evap Purge Monitor tests the integrity of the hoses/tube between the throttle body/intake and the fuel tank. The monitor is a two stage test and runs only after the Evap system passes the small leak test. Stage one is non-intrusive. The PCM monitors the purge vapor ratio and the ESM switch closed ratio. If the purge vapor ratio is above a calculated value, the monitor passes. If the ESM switch closed ratio is greater than calculated value when purge flow is greater than a minimum value, the monitor passes. Stage two is an intrusive test and runs only if stage one does not pass. The PCM commands the purge solenoid to flow at a specified rate to force the purge vapor ratio to update. The ratio is compared to a calibrated specification. If it is less than specified, a one trip failure is recorded. This test can detect if the purge hose is off, obstructed, or the purge valve is not operational.

When Monitored:
After the Evap System small leak test has passed, with the engine running, ambient temperature between 4° C (39° F) and 35° (95° F), with the engine at idle after a calibrated amount of drive time has accumulated.

Set Condition:
If the PCM detects that the purge vapor ratio and the ESM switch closed ratio are below a calculated value, the PCM commands the purge solenoid to flow at a specified rate to update the purge vapor ratio. If the ratio remains below a specified value, a one trip failure is recorded. Two Trip Fault. Three good trips to turn off the MIL.


If you have a new cap and a smoke test shows no leaks, then I would take a close look at the ESM switch.
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I apologize but did not realize that I was getting responses to this. This issue has still not been resolved. I'd like to add some additional information to this.

My truck is also experiencing the following:

1. If I "top-off" my tank, I may experience the truck literally shutting off while driving. It happened this March while traveling and fortunately it was only when I was moving slowly. I've not topped-off since and this has not recurred.

2. Under the center console, while driving, I will here what sounds to me like a solenoid trying to engage unsuccessfully. I produces a rapid clicking sound for a 2-3 seconds then stops.

I have to believe that all these are related issues.

I'm at 201K miles and the body is starting to decay a bit. I'd like to keep my baby as long as I can because it is otherwise a great vehicle. I just cannot justify the expense of exploration that involves dropping the tank.
For what its worth, I had the persistent P0456 code and found out that if you keep you gas tank at least 80 percent full the code will never show up. Its a hassle but you could pass inspection that way. Finally had it fixed, they replaced a canister and another part and the problem is gone. Make sure you clear the code before you do the 80 percent fill thing.
seems like there is a problem with your tank evaporation. can have multiple reasons- either it's the ball-stop at your nozzle which routs the fumes to the charcoal filter or it can also- how you described- that the ball, which floats under your filler nozzle gets clogged up and stuck. the ball is there, if your vehicle turns over, that the gas tank does not run out. you might be able to get to it, when you get your tank out and reach through the hole for the pump. sometimes this happens, when the evaporation valve does not work and the tank gets a vacuum and compresses. How you say, it seems like this is your problem. The clicking, what you hear is likely the soleonoid valve for the evaporation line, which actually closes the line, when the engine is cut off- the sensor recognizes, that there is no air flow and tries to open the valve, which is already open- it will be tacted. Check your evap system. But if you rather ask, instead of try, what people tell you, there ain't nothing anybody can help you with.
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