Jump to content

The RennTech.org community is Member supported!  Please consider an ANNUAL donation to help keep this site operating.
Click here to Donate

Welcome to RennTech.org Community, Guest

There are many great features available to you once you register at RennTech.org
You are free to view posts here, but you must log in to reply to existing posts, or to start your own new topic. Like most online communities, there are costs involved to maintain a site like this - so we encourage our members to donate. All donations go to the costs operating and maintaining this site. We prefer that guests take part in our community and we offer a lot in return to those willing to join our corner of the Porsche world. This site is 99 percent member supported (less than 1 percent comes from advertising) - so please consider an annual donation to keep this site running.

Here are some of the features available - once you register at RennTech.org

  • View Classified Ads
  • DIY Tutorials
  • Porsche TSB Listings (limited)
  • VIN Decoder
  • Special Offers
  • OBD II P-Codes
  • Paint Codes
  • Registry
  • Videos System
  • View Reviews
  • and get rid of this welcome message

It takes just a few minutes to register, and it's FREE

Contributing Members also get these additional benefits:
(you become a Contributing Member by donating money to the operation of this site)

  • No ads - advertisements are removed
  • Access the Contributors Only Forum
  • Contributing Members Only Downloads
  • Send attachments with PMs
  • All image/file storage limits are substantially increased for all Contributing Members
  • Option Codes Lookup
  • VIN Option Lookups (limited)

DIY: 03-04 Boxster AOS

Recommended Posts

This article describes how to replace the emissions system air-oil separator (AOS) on a 2003/2004 Boxster/Boxster S, which is slightly different than on earlier model Boxsters. The photos are of my 3.2L '04 Boxster S Tip.

There are two good writeups on replacing AOS (with procedures for up to '02 Boxsters) that give background and symptoms and I recommend you read prior to doing this repair:




Open the engine access cover; jacking up the car is not necessary on this model year.


There is a quick-disconnect tube readily accessible near the top of the AOS, connecting to the Y-pipe to the intake. [yellow circle in photos] Squeeze the top and bottom of the quick-disconnect (the textured portions) to disengage the plastic barbs. Pull this away from the AOS.


Next, disconnect the lower quick disconnect tube visible from the top [purple circle in photos]. It's disconnected in the same fashion- squeeze the top and bottom, and push away from the AOS. There are a lot of obstructions that force a bad angle; you may need to lean over from the left side of the car or lay on the trunk to find a position with both grip and leverage.


The AOS is held in by two star bolts [red circles in photos]. These bolts are accessed from the top, through the engine hatch. You should be able to remove them with a standard 8mm 6-point socket and 12" of extensions, but you might need a special socket if they're too tight.


A rubber tube comes off the bottom of the AOS, turns 90 degrees, and enters the block [cyan circle in photo]. There are two #^%$#-style hose clamps on this pipe. Use vice grips, screwdrivers, plyers, crowbars, whatever you can do to get this off. With the clamp clear, you can work on the hose. Grip the hose with a pair of pliars and twist it to break it loose; it should slide off. If you can't get leverage, securely grip your pliars, and (gently) persuade it off with a crowbar. The AOS is now free!

Tricks that worked for me on my 04 986S tip and might inspire you: I stood behind the car, and leaned over the trunk to work from above. I clipped a vise-grips to one prong of the hose clamp, and used a screwdriver wedged against the structure of the engine to brace the other end. While using the vice grips as a lever to compress the clamp open, I jammed a crowbar against the vise grips and worked at it until I slid the clamp 1" back from the block. You might get lucky or actually have the right tool and get it off easy, but It took me about an hour of trial & error. Note: I also removed a line off the upper intake manifold and moved it out of the way to get sufficient throw for the crowbar.

View from the right-rear tire well, with tire removed and car on jackstands:



Old AOS I removed: 996.107.026.00

New AOS I installed: 996.107.026.01

Old on left; new on right.


Fortunately, installation is very easy, almost trivial. If your hose is in good condition, remove it and install it on the new AOS. (Take note before you remove it, so you can reinstall it in the same direction.) The hose should be pointing in the same direction as the top-most tube. Do yourself a favor, too- throw the old spring clamps away, and buy some stainless steel worm-gear hose clamps. Tighten the clamp that attaches it to the AOS- be sure to align it so that it won't foul anything when you install it, and so you or the next mechanic might be able to reach it with a screwdriver from the wheelwell. Fasten it tightly; this is fairly low pressure, but you don't want a leak.

Slide your 2nd hose clamp on loosely; align it so that it won't foul, and you can tighten it. Hold the end of the rubber hose as you feed it down, and slip it over the nipple. When you get it about halfway on, you should be able to set the AOS in place, but get it as far on as you can. Position and tighten the hose clamp, reattach the two quick disconnects, replace the two bolts, and you're done! A magnetic socket or mechanic's magnet-on-a-stick helps with getting the bolts in.


Start the engine, and admire your handiwork. You'll probably get a bunch of smoke at first (and the next few starts) as the oil from before burns off, but it should dissipate after a few minutes. Any auto parts store can read & clear your CEL for free, so don't pay the Porsche dealer. [Mine recorded a bunch of cylinder misfires.]

Curious what's in there? Grab a hammer and chisel, and go to town! The base is hollow, in two separate and isolated chambers. You can peep through the nipples and see. The interesting bit is the diaphragm on top:


Edited by grover
  • Upvote 2
Link to comment
Share on other sites

  • 1 year later...
  • 7 months later...
  • Moderators

Yes thank you. Doing this tonight. How long should it take for the massive amounts of smoke to stop when you first start up after replacing?

Depends upon how much oil built up in the intake runners, and how effective you were in cleaning it out before starting the car.

Along with smoking, the oil will not be doing your O2 sensors or cats any favors.........

  • Upvote 1
Link to comment
Share on other sites

  • Moderators

Super thanks. Guessing I can only clean the ends of the hoses and not much else. I'm also thinking about taking the MAF off and spraying it with the Crc maf cleaner. Any other ideas?

Cleaning your MAF won’t do much as the oil is behind the throttle body, inside the intake runners themselves. The MAF is upstream of where the AOS connects to the intake system. When one of these AOS failures gets out of hand, it can actually flood the intake with liquid oil, causing terminal hydraulic lock of the motor.

Do a search, this has been covered many times on multiple sites.

Link to comment
Share on other sites

thanks for the advice.

Got it done last night. Pretty easy once you figure out how to get your hands around the triptronic to that hose on the side. I had the special pliars for the bottom hose clamp and got that one from the top. Unfortuantely I broke the hose on the very top when unhooking it. Brittle as heck. Going to the dealer to hopefully finish this up today.

Link to comment
Share on other sites

  • 6 months later...
  • 2 years later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.