# hissing sound on 99 passat



## freddy88 (Mar 27, 2010)

hey everyone was wondering if you could help me out. Just traded for this car and was wondering if it is normal for my car to make a loud hissing sound when it is cold. I first start it and the rpms are about 1100 and it makes loud hissing sound until it warms up and drops below and sound stops. I looked underneath and it looks like there is a open plastic piece that comes down and is blowing out air until it warms up and rpms drop. Could you please help me out, thanks.


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## afawal (Oct 18, 2005)

*Re: hissing sound on 99 passat (freddy88)*

Describe the hissing a little more.... does it get louder with RPM's, or is it a contant hiss? Take pictures of what you are describing in your initial post.
I had an issue with a hissing sound and it was actually coming from the tranny. Long story.....


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## spitpilot (Feb 14, 2000)

*Re: hissing sound on 99 passat (afawal)*

On cold start up there is a secondary air injection pump that runs to blow air into the exhaust manifolds to "lite off the cats quicker"....if one of the air lines is broken/cracked or has gotten brittle and fallen off its connection...this air will leak out...you should get a CEL with "SAI low flow" code if this system fails. http://****************.com/smile/emthup.gif


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## cealer (Feb 12, 2009)

*Re: hissing sound on 99 passat (freddy88)*

Thanks for the responses. I know I'm not the OP but I just noticed this on my passat last night came on here to post and saw the topic had been made just a little bit earlier! I only noticed this noise after a horrible vibrating noise from a cap on my tension roller finally stopped after the cap blew off the car, lol. Anyway thanks for the info!










_Modified by cealer at 8:15 AM 4-1-2010_


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## O_o (Nov 12, 2009)

*Re: hissing sound on 99 passat (spitpilot)*


_Quote, originally posted by *spitpilot* »_On cold start up there is a secondary air injection pump that runs to blow air into the exhaust manifolds to "lite off the cats quicker"....if one of the air lines is broken/cracked or has gotten brittle and fallen off its connection...this air will leak out...you should get a CEL with "SAI low flow" code if this system fails. http://****************.com/smile/emthup.gif 

^^ this.


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## freddy88 (Mar 27, 2010)

*Re: hissing sound on 99 passat (spitpilot)*

thank you i actually got the car checked out today and it did say something about that secondary injection being low. Ill have it checked out and let you know whats up greatly appreciate it


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## freddy88 (Mar 27, 2010)

*Re: hissing sound on 99 passat (spitpilot)*

thank you actually had car checked out today and it threw the code for low secodary injection, ill have it checked out and let you know what it was, i greatly appreciate it cuz it's been driving me nuts and just wasnt sure if it was supposed to do that. http://****************.com/smile/emthup.gif


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## freddy88 (Mar 27, 2010)

it was the hose under the right front bumper it came unclipped


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