New Buzz/Hum under dash

[SANOLS1]

I've had my C5 A-4 for a couple of years now and I am noticing a hum after starting. It only last about 30~45 seconds then it stops. It sounds like it is coming from the left of the steering column under the dash somewhere. I seem to recall something about this in a thread a year or so ago but I couldn't find it using the forum search. Anyone have any ideas. This may be normal and I am just now noticing it. Appreciate it.

 

[99WhiteC5Coupe]

I've had my C5 A-4 for a couple of years now and I am noticing a hum after starting. It only last about 30~45 seconds then it stops. It sounds like it is coming from the left of the steering column under the dash somewhere. I seem to recall something about this in a thread a year or so ago but I couldn't find it using the forum search. Anyone have any ideas. This may be normal and I am just now noticing it. Appreciate it.

At cold vehicle start, there is an electric air pump that turns on for about 1/2 - 1 minute, which is part of the emissions control system. The pump is located in the left front of the engine compartment. This is probably what you hear. I hope this helps - good luck.

 

[SANOLS1]

Thank you for the reply. My question now is should I only hear it when the engine is cold? It happens every time I start it, even when hot. It is quite noticeable. Thanks again.

 

[Mr. Lucky]

My question now is should I only hear it when the engine is cold? It happens every time I start it, even when hot.

The engine doesn't have to be "cold," just cool enough so that it's running in open-loop mode (≤ 136°F coolant temps). Actually, there is a bit more to it, but 136° will get you in the ballpark.

 

[SANOLS1]

After reading that I wonder if my tune has anything to do with it. Since I had a supercharger installed a while back and the tune is nowhere near stock do you think that might explain why I hear this even when hot. If I turn off the car for only 1 or 2 minutes, I hear it all over again. Thanks for the info.

 

[Mr. Lucky]

After reading that I wonder if my tune has anything to do with it. Since I had a supercharger installed a while back and the tune is nowhere near stock do you think that might explain why I hear this even when hot. If I turn off the car for only 1 or 2 minutes, I hear it all over again.

That short of a time period isn't even long enough for the cats to cool down, so it definately can't be the AIR pump. I'm more inclined now to think it might be related to the EVAP canister purge solenoid, which is in the area you describe (between the firewall and driver-side fuel rail). Have you scanned for any stored codes?

 

[SANOLS1]

That short of a time period isn't even long enough for the cats to cool down, so it definately can't be the AIR pump. I'm more inclined now to think it might be related to the EVAP canister purge solenoid, which is in the area you describe (between the firewall and driver-side fuel rail). Have you scanned for any stored codes?

I think you've nailed it. Thanks for the Tip.