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Discussion Starter · #1 ·
Hello everyone, I just wanted to send out a quick FYI to help diagnose and fix code PO456 small leak detected.

After months of dealing with this on again, off again codes, and reading many how to service bulletins without a viable conclusion to this purpetual never ending story of PO456 SMALL EVAP LEAK.

I did all the right checks including a negative pressure test, smoke test, changing out the fuel cap, both purge valves and all the hoses. to no avail, the code kept reappearing.

Finally it occurred to me that after all of the above mentioned test and not being able to resolve the issue, I decided to check the pressure again and finding no decernable pressure changes, only this time when removing the guage, and replacing the internal valve stem I began to hear a very low hissing sound after replacing the valve stem and ensuring the sound had stopped, I have found the culprit.

verification was done by placing a bit of low viscosity grease under the cap, waited overnight when cap was removed the next day, I found that the grease had been sucked down into the valve housing around the valve stem....I was going to eliminate the port entirely but it was cheap enough to replace.
 

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Hello everyone, I just wanted to send out a quick FYI to help diagnose and fix code PO456 small leak detected.

After months of dealing with this on again, off again codes, and reading many how to service bulletins without a viable conclusion to this purpetual never ending story of PO456 SMALL EVAP LEAK.

I did all the right checks including a negative pressure test, smoke test, changing out the fuel cap, both purge valves and all the hoses. to no avail, the code kept reappearing.

Finally it occurred to me that after all of the above mentioned test and not being able to resolve the issue, I decided to check the pressure again and finding no decernable pressure changes, only this time when removing the guage, and replacing the internal valve stem I began to hear a very low hissing sound after replacing the valve stem and ensuring the sound had stopped, I have found the culprit.

verification was done by placing a bit of low viscosity grease under the cap, waited overnight when cap was removed the next day, I found that the grease had been sucked down into the valve housing around the valve stem....I was going to eliminate the port entirely but it was cheap enough to replace.
I'm surprised the smoke test didn't catch that if the leak was a result of a crack in the EVAP service port housing. Usually, a leak from that port is due to a faulty shrader valve (...this is also why smoke tests are really best conducted from the hose that plugs into the purge valve).
 

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Discussion Starter · #3 ·
I'm surprised the smoke test didn't catch that if the leak was a result of a crack in the EVAP service port housing. Usually, a leak from that port is due to a faulty shrader valve (...this is also why smoke tests are really best conducted from the hose that plugs into the purge valve).
Excellent point !! I didn't think of that, I suppose the smoke might have been able to expose the location or source of the leak if the smoke test were to be started anywhere other than the schrader valve, maybe its just because that's what I have always seen and done in the past....what surprised me the most is that the negative pressure gage didn't catch it either, that had been done numerous times, Oh god I just thought of something, Maybe the leak hasn't been repaired, and that I only caught and replaced the service port crack, possibly due to age of the housing or something that would have caused the crack anyway....Hmmm, time will tell.:unsure:
 
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