FRUNKenstein

Bought the '06 CS a couple of months ago. Halogen headlights. Check Dipped Beam Error. Both sides low beams not working. Pulled one side and checked the bulb. Here's a pic, bulb looks good:



Obviously there's something more nefarious than a burned out bulb, plus I see lots of threads in here on Dipped Beam Error and non-functioning headlights. I come from the 996 forum, so I know it's time to start researching and prepare for the worst:
Will I have to spend big bucks to replace the headlight assemblies?
Is it some esoteric electrical problem buried deep inside the main wiring harness?
Is it a sign that my IMS bearing is failing?

Well, I am proud to report that as of today, both headlights are shining brightly.
Here's what I learned over the last couple of months:

First, my car is apparently one of about a dozen Cayennes ever manufactured that DO NOT have Xenon headlights.
Second, "Dipped Beam" does not mean the headlight moves. Or does anything exciting or cool. "Dipped Beam" is apparently just fancy Euro-speak for low beams.
Third, if you're looking for liquid electrical tape to seal up some cracked wiring insulation, forget the auto parts stores and go straight to Home Depot. Go to the electrical department. They have it. In 4 different colors.
Fourth, if the wiring harnesses that plug into the back of the headlights are cracked and flaking, Sunset Porsche has the best price for replacements.
Fifth, you don't need to remove the light-holder-platform thing to swap out the harnesses or free up the black plug that you plug the harness into. Just gently muscle it up and toward you as you slide the plug out.
Sixth, I found the mod about altering the headlight harness plug to free it from the headlight platform so the plug doesn't unseat when going over bumps. Shaving the ear clips off the white headlight plugs is really easy. The first one I used a dremel tool. The second one I used a box cutter. Box cutter was easier.
Seventh, halogen headlights are much simpler than Xenons. No ballasts or control units to screw with.
Eighth, if one halogen headlight is burned out, the other one will work just fine. (I saw it written somewhere that one side burned out will cause the other to not light - ain't true)
Ninth, if your headlights aren't working, don't forget that the fog lights are a temporary substitute.
Tenth, sometimes the most obvious thing really is the problem. That bulb shown in the pic above - it turned out to be bad. When I pulled the other bulb, the one I didn't bother to check at the start, well it was bad also. Two $10 H7 bulbs from Walmart later, and voila, headlights now worky.

tjrob2000

You can't always tell a bulb is bad visually, but that one definitely is. The filament coils are too close together and sagging. That is why it wasn't working. Just my $.02.

FRUNKenstein

Yeah, I was looking for a dark spot or a broken coil. Lesson learned - I should've just swapped the bulbs out as the first step in troubleshooting. Had I bothered to pull the other one when I first got the car, I definitely would have changed it as it had a big dark spot. As a rule, I always change headlight bulbs in pairs, so it would have fixed the problem entirely and saved me a lot of time and about $100 in wiring harnesses.
But, as an avid Rennlist member, because both sides were not working and the one bulb I initially pulled looked good, I overanalyzed and assumed the worst. Ugh. Maybe I'll save someone else from making the same mistake.
BTW, this same thing happens often with the 996 ignition switch. The electrical portion is a $12 part that takes 20 minutes to swap and almost always fixes a crunchy or stuck switch. Despite all the threads on it, people routinely report spending hundreds of dollars having a mechanic change the entirely assembly.