As a cayenne (955) owner, clearing the cowl drains was high up on my agenda for the PTT!
Much easier than a cayenne to remove the front wheel arch liner. About 4 torx screws and three plastic nuts. (Obviously remove the wheel first). The liner is quite loose and nice and easy to get out.
simply pull the rubber valve out, clean it out and put back.

Wheel arch looking back towards passenger compartment. Valve is circled in red

30 mins- 1 hour if, like me, you took the opportunity to clean up under there and remove all the dirt.

 

Close ups

 

nice

 

Thank you for this! Can you also explain why this clean out is needed?

 

Certainly.
On a cayenne it is common for these to become blocked up with leaves and dirt.
Water drains off the windscreen and around the wipers down into a void behind the wiper motors, then out of the valves above. The water in there has nowhere to go if these are blocked and comes out on your carpet, usually the passenger side through the ventilation system, and corrodes all the wiring which runs under the carpet including your fan.
I wasn’t sure if it was a Panamera problem but didn’t want to take the risk. Mine were a little dirty but running fine - the valve looks to be a different design. (it’s designed as a one way valve on the cayenne).

lots of videos and DIY articles about for Cayenne (955,957 and 958 all affected).
this for example https://rennlist.com/forums/cayenne-...clean-out.html

 

Can the same be accomplished from the engine bay using compressed air? That’s how I did it recently based on the YouTube video below (skip to 6:54), but wasn’t sure if this is clearing the same drains or if it’s still necessary to remove the wheel and clean it from underneath. Thoughts?

 

Yes. Cleaning them from the cowl is fine. You should only really have to pull the plug and clean it out if other methods do not work first.

 

thanks! When you say “if other methods don’t work first” - how would I be able to tell?

 

Put a hose against the windshield on each side and make sure it drains out behind the wheels. If it doesn't (after cleaning at the cowl) you need to do what the OP posted here

 

thanks, much appreciated