I have a 2003 Audi A6 3.0 and the Malfunction Indicator Lamp has been coming on recently. I've sent my car to the mechanic to get this checked out every single time and gotten a Code P0456. When they check it out, nothing appears to be wrong and they get the light shut off. However, after resuming driving for a certain mileage, the light turns back on. Has this happened to anyone else? I'm fed up with worrying about the MIL and possible problems that are not being detected. What should I do?

 

Try this thread.

 

I agree with the thread chefro gave you, its most likely a bad N80 valve (EVAP regulator valve) that sits on top of the airbox. When you first start the car, there should be a loud clicking from this valve, if you don't hear any clicking, or if you smell gas coming from the valve thats the problem.

 

Well first of all, there is a clicking noise that can be heard when I start my car, so it is not that. Second, is there anywhere that I can find a diagram of the Audi engine, just like the one of the Bentley? I've looked everywhere and I can't find one. Thanks.

 

Well the valve could still be leaking, your best bet is to have someone pressurize the EVAP system and inject smoke to see where the leak is. The tech should check the gas cap as well.

 

So I got it checked and apparently there are no leaks. The gas cap is on fine as well. I am puzzled. Next plan of action?

 

Replace the hoses around the purge valve, or at least replace those "pinch" type clamps with better ones. See what that does for you.

 

My 2005 A4 has had a P0456 code several times over the past year. Goes on and off. I took it to the dealer a few times and they always tell me to make sure the gas cap is tight. After it continued, I replaced the gas cap ($60 from audi. OUCH!) but it didn't correct the problem. It is in the shop now (not the dealer) and they are saying it is the purge control valve. $152 installed.