P0456 code
AudiWorld Super User
Joined: Feb 2010
Posts: 3,066
Likes: 37
From: Fort Worth, Tx
No easy answer unless you didn't tighten your fuel cap. Other than that, someone has to go find the leak which goes from the gas filler in the back up to the engine bay.
Last edited by lyleswk; Aug 3, 2020 at 11:50 AM.
AudiWorld Super User
Joined: Jun 2008
Posts: 2,284
Likes: 100
From: Fallbrook, CA
Could be lots of places. As lyleskw said, gas cap. But could be the EVAP valve which 'purges' fuel vapors from the carbon canister. There are also plenty of hose connections such as to the carbon canister, which could be where the leak is. My own '05 had a leak that was difficult to pin down, until my son-in-law discussed with an Audi tech; rocks thrown against the rear fender liner can crack the hard plastic line behind it, and that's what the problem was, in my case.
The typical EVAP test uses engine vacuum to make the atmosphere power an oscillating pump. That pump is stopped once pressure reaches the point that a pressure-operated switch opens. The system waits as the pressure either holds steady or gradually decreases. If pressure holds long enough for the timer to expire, the test is OK. If the pressure switch contacts close again before times's up, a small leak is detected. If the switch never opens in the first place, it will then be logged as a large leak.
The typical EVAP test uses engine vacuum to make the atmosphere power an oscillating pump. That pump is stopped once pressure reaches the point that a pressure-operated switch opens. The system waits as the pressure either holds steady or gradually decreases. If pressure holds long enough for the timer to expire, the test is OK. If the pressure switch contacts close again before times's up, a small leak is detected. If the switch never opens in the first place, it will then be logged as a large leak.
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