Lately it seems my HID headlights are getting dim and I use the front fog lights to help. The fog and high beam lights are both bright, just the HID seem weak. Yes I have a perfectly good 6 month old H7 Interstate battery and yes my alternator is putting out 14.0-14.3 volts while headlights are on and I'm driving at 55MPH. Just wondering if there is any BCU settings for voltage to the lamps or perhaps the bulbs are just ageing. Never had HIDs go dim on my Volvo or Audi. Any thoughts?

 

You didn't say what year your Cayenne is but I think all 955/957's are probably reaching end of life for their HID bulbs.

They do get dimmer over time and their color output shifts. They turn purple for a little while before they completely burn out.

I'd suggest replacing the bulbs (it's super simple. Check your owners manual for the procedure). Cleaning the housing thoroughly, sanding and polishing if needed. If that still doesn't fix it, then get out the multimeter and confirm that you're actually getting your 14V at the lights. The wiring harnesses I think are known to have issues over time.

 

Sorry, my user ID is Turbo S but I did forget the year, it's an '06.. Thanks for the reply. I've had the assembly out several times for polishing and other lamp replacement. As you say "super simple" wrench for it is in the basic tool kit by the spare too.
My '06 Volvo and my '00 Audi S4 still have the original bulbs and they don't show any aging. Which is why I asked here to a larger audience. Guess I'll go researching bulbs. Anyone been there already that has some first hand knowledge to share?

 

Don't buy the knockoff ones. Make sure you get the namebrand D1S bulbs from a reputable seller and not ebay or amazon.

 

like others said, xenon bulbs go dim over time. Not sure how it is on 955 but on 957 low beams are used as daytime running lights so that contributes to that as well. DRL seems like an afterthought as similar era cars use high beams at lower output for DRL...

Anyway I got D1S Philips 85415XV2 XtremeVision 4800K from xenon depot and they're worth the cost. Noticeable difference compared to my old bulbs, which were barely good as halogens.

Also, you can check the bulbs before buying new ones. Check my build thread for pix.