I recently purchased a 2005.5 A4 B7. I've been having problems filling it up with gas because it kicks the pump off every gallon or so. I've searched through the forum and found that it may be the charcoal canister or leak detection pump. I think I know how to troubleshoot it but I can't figure out how to get the hoses off to find out which one is the problem. It appears to be a ring that needs to twist or slide but I'm afraid I'm going to break it. Can someone explain how to get both of the hoses off to determine what the problem is? Also can they be cleaned out or do they need to be replaced? If they need replaced, where would be the best place to purchase? I also have a knocking sound that appears to be coming from the same place. It happens after the car is warmed up at idle and for about 20 seconds after I turn the car off. Are these problems related or two separate things that need to be checked out? Sorry for all the questions but I'm new to Audi and need some insight. Thanks.

 

Definately vapor charcoal canister. I have no idea where it is as the dealer did mine on warranty. Maybe someone will chime in who has a book. Not sure about the other problem.

 

I understand that the canister is located in the trunk on the right side by the spare tire. It looks like a fair size black plastic box with 3 or so hoses plugged into it. I believe a new box cost around $180 Also the noise you might be hearing is the frequency valve that is going bad. This will set a CEL if it fails. The reason why I understand you will have trouble filling the tank is because this canister has a vent line which I assume is blocked/bad so when you pump fuel into the tank it blows back on the gas fill nozzle and automatically shuts off.

 

Thanks for the info. What/where is the frequency valve? Also, how do you remove the hoses that go into the canister? Thanks.

 

The charcoal canister gets clogged with items it has filtered over the miles of the car. I had mine done about 83000 miles but sufferd with it for a couple thousand prior to taking it in.

This is typical on mid to higher mileage cars.

 

what?

 

When you try to pump gas in but the pump keeps shutting off like the car is full. You have to baby it to get gas in. It's the Charcoal vapor canistermclogged up. Happens when the miles start to get high.

 

Bump because I am having the same problems on my 05.5 a4 3.2. So I think I got the canister figured out but the nocking noise has got me stumped still. Mine comes from under the driver side rear seat and seams to do it when less than 1/2 tank. I've just replaced the fuel pump recently too if that helps.