[1stiski]

What is exactly going on when you start the 451 with a cold motor . The vacuum noice makes me curious . It is kinda cool , some kind of fan action ?

 

[Ryanxiety]

I believe that is the Secondary Air Injection Pump, but I only have a basic understanding of what it does, and may be a little bit wrong, so I won't try to detail it.

 

[1stiski]

So this is something for the fuel injection and has cold start enrichment purpose . Once the car is warmed up , it won’t do it again with a warm engine .

 

[MB DNA]

Just another smart "feature" - https://www.smartcarofamerica.com/f...tarting-engine-cold-64345/?highlight=WHIRRING

 

[Ron Ream]

It sounds like a Hoover.... yet my floors are still dirty.

 

[jwight]

Not sure on the 453; that's what it is on the 451.

 

[jetfuel]

...and btw...if the noise gets louder...serious rubbing noise.... it's probably full of water...that was my finding when my bride's cabrio started to make the noise....installed the one from my car and problem solved...

Jetfuel...no cat no pump needed..

 

[1stiski]

Not sure on the 453; that's what it is on the 451. <img src="http://smartcarofamerica.com/forums/images/SmartCarOfAmerica/smilies/tango_face_smile.png" border="0" alt=""
title="Smile" class="inlineimg" />

This is on our two 451’s , not the 453 .

 

[SmoovJazzy]

I also have this sound on my 2003 New Beetle Turbo S. It's the secondary air pump that forces air into the catalytic converter upon startup. (That is what found in a video on Youtube) On my 2013 Smart Brabus it sounds pretty muffled, on my Beetle it sounds like a jet engine which means it needs to be replaced. Once the Smart starts screeching, like my Beetle I will replace it too. Apparently, when the bearings in the pump go bad they get louder and louder. Eventually, it will throw a code in both cars. The pump for the Beetle is around $90.00, for the Smart they are $150.00.

 

[OliverB]

Not sure on the 453; that's what it is on the 451.

The 453 has its own version of the same pump. Slightly different noise than the 451.

 

[SMRTN8R]

No worries, it's just a built in vacuum cleaner that doesn't clean. It's the secondary sump, they all have it.