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Code PO456

Tiny
NILSA1977
  • MEMBER
  • 2008 SUBARU FORESTER
  • 2.5L
  • 4 CYL
  • 4WD
  • AUTOMATIC
  • 99,451 MILES
When I drive my vehicle for more than half an hour, the cruise control light flashes and my check engine light comes on. The code that is showing up is PO456 and when I had it cleared all three times, afterwards, it hesitates to start. I have checked the fuel cap and gaskets. They look okay. What else could the problem be?
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Sunday, February 4th, 2018 AT 3:10 PM

4 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,414 POSTS
P0456 is a very small EVAP leak. That means the leak is not something you are going to see with your eyes as it is.020" For a visual of what.020 looks like the hole in this letter- o -is larger than.020".

It can be virtually anywhere in the EVAP system. Resetting the code does nothing. You need to have a smoke machine connected and then look hard for the tiny leak. It could be under a flake of rust or at a hose connection or inside a valve. The reason the car hesitates is because clearing the codes does more than erase that one code, it also resets the engine computer so it has to relearn some of the data it needs to run.
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Sunday, February 4th, 2018 AT 5:12 PM
Tiny
NILSA1977
  • MEMBER
  • 3 POSTS
I also have a bad habit of fueling up the vehicle while it is still running. Could this also be the cause?
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Sunday, February 4th, 2018 AT 5:34 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,414 POSTS
No, that would cause a P0440 which is a large leak. Plus the EVAP system would not run the leak test if the tank is over 3/4 full.
What you have is a leak that could be hard to find. That is why I suggest a shop with a smoke machine. That will fill the system with smoke that should leak out of the problem spot. Then it is a matter of repairing the problem. Anything in the attached picture could be the source of the leak.
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Sunday, February 4th, 2018 AT 7:53 PM
Tiny
NILSA1977
  • MEMBER
  • 3 POSTS
Thank you so much. I appreciate your help.
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Sunday, February 4th, 2018 AT 8:14 PM

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