Fault Code P0456: Evaporative System Emission Leak
 

I had O'Riley's read the fault code for the MIL light that came on couple weeks ago, and got Fault Code P0456: Evaporative System Emission Leak, and then in parenthesis it read "very small leak".

I'm a DIYer on routine maintenance, but with this one I have no idea where to start. It could be a sensor somewhere... anyone had this before? I might have to take it to the mechanic.

I believe this is a catch-all code for a vacuum leak. The only advice I can give is to start at the gas cap and if that's not it, start snooping around the engine compartment looking for a vacuum line that might be loose. There is a vacuum diagram sticker in the engine compartment and you might try following that. Also, did you have O'Rileys reset the light? If it was a gas cap, and it's now on tight, the light might not come back on.

One more thing- When we run our cars through emissions testing in Washington State, they take the gas caps off and hook them up to a vacuum source to test for leaks. I'm sure they'd perform that test free of charge.

No, I didn't ask them to reset, I didn't know they could do that, I'll come by and ask them to and see if works. I would think that if it was the gas cap, the light would reset itself at the next startup, I'm almost positive it would, since when the car is off and then turns on, it performs a self-diagnostic. for example, in my bmw, I often get all sorts of error and warning messages, like during very cold weather, or when I didn't drive it for quite some time, all I do is restart the car and they always go away, unless it's a real problem that needs to be fixed.

Greatly appreciate the advice, I'll check the vaccuum hoses and go from there.

Usually, and I'm not exactly sure in this case, there has to be multiple occurrences before the light will come on. Especially if it's classified as a small leak. I bought a code scanner from my local auto parts shop and it will display any of the basic codes that a modern engine can throw. Don't confuse this $60.00 scanner with VAG-COM which is the VW auto group scanner and much more involved. The $60.00 version will display OBDII codes that all cars can display since about 1997. When you hook up the scanner to the OBDII port, it will show all codes that are either "pending' or actual codes that are making the check engine light illuminate. To eliminate nuisance lights, most codes need more than one occurrence to turn the check engine light on. These are the "pending" codes. If you erase all codes, you can start fresh and monitor the frequency that the code is being generated. This means that it still could be a gas cap. I recommend that you have them reset the codes and see what happens. If the light comes on again and you've checked for obvious leaks, it's probably time to take it in to the dealer. They'll hook up it to VAG-COM and probably have an answer for you in very short order.
Good luck !

A lot of those codes reset after two weeks anyway.
Quite a few of the early production were overcharged with evaporator fluid anyway so (the optimists view) it may even work better now ;)

Don't underestimate this problem. My 2010 Q5 has been in and out of the dealer 6x since Nov2011 for the same problem!

See this thread:

https://www.audiworld.com/forums/sho....php?t=2817035

Had the same code on my 07 Q. Reset the codes a few times myself but code and CEL keep coming back. Finally went to dealership and had a bad oxygen sensor and one of the front catalytic convertors had to be replaced. Not under warranty--costly.