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Discussion Starter · #1 ·
Hey guys, have had the code for a while P0455 OBD11 says Evap Gross Emission control system leak. I replaced this evap valve with no change. I will attach a pic of a valve in case I am wrong. Any ideas would be great. Valve on top of air box. Thanks guys


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That's one possibility but there are many others. Check the gas cap first. Then the pipes to/from the tank to the valve. Lots of threads on various EVAP problems can be found here but they all pretty much boil down to something is leaking. Often it is the gas cap.
 

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Thank you, changed the gas cap with no difference. I tried searching on tapatalk with no threads found. Maybe I must be on thr website. My 2 main questions are 1. How does the computer know there is an issue. 2. Does it effect emissions? I have not noticed any change of how the car runs. Line check an tank inspection next.

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Here's a thread, I'm sure there are more
 

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If it's not the easy fixes, look into this one:
 

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It's saying you have a large leak, but you may not have a leak maybe a sticking valve. If you have access to a vacuum gauge, it would really help. Disconnect the electrical connector and the vacuum line, hook up the vacuum gauge. With the car running, see if you are pulling vacuum thru the switch. There should be none. Try tapping on the valve, if it starts moving around, good sign its sticking. Check the N80 also, same way.
 

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Discussion Starter · #7 ·
It's saying you have a large leak, but you may not have a leak maybe a sticking valve. If you have access to a vacuum gauge, it would really help. Disconnect the electrical connector and the vacuum line, hook up the vacuum gauge. With the car running, see if you are pulling vacuum thru the switch. There should be none. Try tapping on the valve, if it starts moving around, good sign its sticking. Check the N80 also, same way.
Hey Coach, thanks for the input also, hoping to check into these issues this weekend. Which valve is thr N80 again? Is it the boost control valve? Side note. Few months back I got rear ended in a storm. The kids subaru bounced off the the right rear bumper but over the last few weeks I have heard a heavy rattle as something might have come loose lol. Have not had a chance to check yet obviously. Just thought I would add for discussion purposes lol. Thanks for all the input guys. I have plenty more issues with the car I will be hitting your B5 brains with.

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Check the tubing under the gas door between the filler neck and the gas tank. A broken part there could cause this problem and if the car was hit in that area something may be broken.
 

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. How does the computer know there is an issue. 2. Does it effect emissions? I have not noticed any change of how the car runs. Line check an tank inspection next.
Gasoline venting from a fuel tank straight to the atmosphere is a major concern, regarding emissions. The ECU checks that by pumping up a little air pressure in the fuel tank and associated hoses/carbon canister, etc. Then the pump stops and a timed test starts. Depending on how long it takes for the pressure to drop and trigger a pressure switch, the ECU determines whether there is a large leak, a small leak, or no/insignificant leak. The pumping is done by the Leak Detection Pump, or LDP. The LDP has an electrical solenoid valve to control the pump, and the pressure switch. The LDP does not use electricity to run, but relies on engine vacuum for "power". If you listen at the left-rear wheel well after starting the car, you should hear a rhythmic thumping. It can also be forced to run using VCDS software. This condition won't affect how the car runs.

My '05 A4 had that fault, and it was difficult to pin down. Eventually we learned from an Audi tech that sometimes a rock thrown against the rear wheel liner can break the plastic hose behind it, and that's exactly what was wrong.
 
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