S4 Bi-Xenon O Ring Fix with Bonus
 

Like everyone else, I had the dreaded problem with my S4 Bi-Xenon ecode headlamps fogging up whenever it rained or there was high humidity. I never noticed this with my original DOT Xenon lights. I have had the S4 Bi-Xenons on the car for a little over a year now, and the problem seemed to be getting worse over time. I finally did the "umbrella" mod a few weeks ago and this seemed to solve the problem for a few days, but then sure enough, the driver's side started to have a little bit of fogging again. I resolved to do the "O Ring Fix" next, especially after the owner of the shop where I have my car worked on gave me a strange look when he saw my tyvek "umbrellas" over the headlights. I had just removed my headlights and front bumper in preparation for my K04 and DSMIC installation. He had a hard time keeping a straight face when I told him this was an accepted fix on the forums for the fogging problem. BTW, I obtained the tyvek by cutting up a FedEx envelope - free mods are great!

Anyway, I purchased the O Rings from Home Depot. As described in DD's DYI, they are #6 7/16" OD and 5/16" ID. Stock #96723. You can find them in the Plumbing Aisle in a box of 10 for less than $ 2.00 - such a deal! I originally had some trepidation about removing the headlights to do this and throwing the headlights out of alignment, but they were already out of alignment from the turbo/intercooler install, so what the hell. I didn't even have to unclip the headlight harness to do the O Rings. Removed the cover to the headlight height adjuster as in the DYI, and merely pulled the adjuster shaft straight out. If you don't turn the shaft as you pull it out (sounds nasty) you won't alter the headlight alignment. It was amazing how much crap had accumulated under the cover and hole for the shaft. Cleaned all this off, removed the old O Ring and replaced it with the new one and lubricated with powdered graphite. Put everything back together and put the headlights back in. It literally takes less than 5 minutes a headlight to do this. The old O Rings didn't seem to be totally round, so this must be the reason moisture is getting past them.

Here's the bonus. Since I did my USP bumper swap in the Spring, I had an uneven gap between the headlight bottom on the driver's side compared to the passenger's side. I realized that the plate that the headlight slides onto with the two lower fasteners has some adjustment to it. There are two Torx 30 screws on the underside of this plate for adjustment. Just loosen these and you can adjust the headlight gap to the fender. Clever Germans! This took me about another 30 minutes to get the alignment of the gap right. Altogether, less than an hour spent solving two very annoying problems.

So far, both headlights are dry as a bone with no recurrence of the fogging issue. It amazes me that Audi hasn't issued a TSB to the dealers regarding this simple fix. Instead of telling people "they all do that" and even replacing people's headlights when they give in, this fix costs less than 40 cents in parts and a quarter of an hour in labor. It would sure make a lot of pissed off Audi owners happier!

tracking for later reading.

They have issued a TSB on this subject, sorta....
 

The TSB does not differentiate the difference between "light misting", and heavy water condensation accumulation, that does not resolve quickly. It does not address the specific variations in configuration used by the S4/A4 halogen/xenon, and the S4 Bixenon designs. The only comment made on the heavy water problem, is to find and fix any leaks that exist. There is no guidance regarding how to tell what problem is at issue. The symptoms are similar, yet the causes are not related between the two situations.

I tried the O ring fix and event went to a hydraulics distributor to get the closest sized ring
 

I installed the new rings and used powdered graphite for lubricant. When I put the adjustment arm with the new O ring back into place the fit was very snug so I was pretty sure no water would ever get into the housing anymore.

The issue is when one has to do an adjustment on the headlight.

I used an allen key to try to aim the beam a little higher and I ended up snapping off 2 teeth from the plastic gear since the adjustment are would not move as freely as it did before. Even with the OEM O ring in place the adjustment arm is a bit stiff to move, try it now with the new O ring in place.

So people that do this O ring replacement please keep in mind that while it does fix one problem if anyone tries to adjust your headlights it might cause some damage.

No problem adjusting lights after fix
 

I had to lower my passenger side a bit. Prolly out of alignment after the K04/DSMIC install. I used a 6mm hex T handle to adjust with no binding or other problems. The #6 O Rings seem to be a perfect fit for me.

I'm not saying adjustments can't be done but people changing O rings should be careful making them

Awesome, I'm going to go buy some tomorrow...
 

by the way don't make the gap too small because I bet the bottom side of the headlight could potentially scratch up the bumper since there is probably movement over rought roads and bumps.

I find that if you don't get the tabs on the bottom of the headlights into the slots correctly the gap is way off. Once they are in the slots it looks perfect.


"#6 7/16" OD and 5/16" ID. Stock #96723. You can find them in the Plumbing Aisle in a box of 10 for less than $ 2.00 " <---Awesome info!

nicely done!

The new O rings must not be to tight. Powdered graphite for lube only....
 

The fit of the new O rings, can be a bit fussy, to insure that they seal, yet don't cause to much drag. Powdered graphite ONLY, will lube the tighter fitting O rings, preventing any sticking.