Can't even find a mention on the German site - which is unusual, since it's a common accessory. My guess, based on past TüV experience, is that it WILL be mounted under the driverseat though ...

 

This is from A4 B8 but might be relevant... maybe same parts even:

Finnish source: http://www.ultimatevw.com/keskustelu/?cmd=aihe&id=10753&sivu=391

Audi has also had factory extinguishers that are installed in the outside interior wall of the passenger footwell in some models.

 

fire extinguisher will not mount properly under S-line or S seats.

 

Why is that?

This is what I've found in ETKA. It shows two types:
1.

2.

(sorry for polish language)

Are you sure that it won't fit under the seat?
No. 1 must be the version mounted in the footwell. It won't look good...

 

Alkivar:

That would be kind of ironic since the seat mounted fire extinguisher is actually pictured in that ETKA image with sport seat (s-line or normal). Not S5/S sport seat though, so no comments on that.

Google Audi factory fire extinguisher in the pic search, you will find a picture of the footwell version. Or download brochures of Audi models from audi.de and they will show it... At least used to.

 

that is not even an A5 seat pictured in ETKA the cushion pattern is wrong. that is the A4 B7 seat in the diagram (both the B8 A5 and the B8 A4 dont match). they just haven't upgraded the diagram, only the part numbers as is quite common with ETKA.

as for googling, I have, and no I cant find it in the Audi.DE PDF's either.

 

Just wanted to complete this thread by confirming that OEM fire extinguisher fits properly without any modification under S5 seats.

Part number is 8K0098277 and everything you need for install is there: fire extinguisher, all brackets, screws and other bits.

Installation is quite easy, here is OEM manual:
http://hotfile.com/dl/54242489/678fd42/Feuerloescher_A4_B8_English.pdf.html

I had to remove the storage shelf from under the seat, so it is for sale now if anyone is interested.