Porsche Cayenne Pano Roof Drain Water Test + Clear Guide | 958 Rear Sunroof DIY & Amp Buzzing Issue

Porsche Cayenne Pano Roof Drain Water Test + Clear Guide | 958 Rear Sunroof DIY & Amp Buzzing Issue

Water leaks in Porsche Cayennes, especially those with a panoramic roof or sun roof like my 958, are unfortunately common and often trace back to blocked sunroof drains.

Whether you have a Cayenne 955, 957, or 958, or even a VAG sibling like an Audi Q7 or VW Touareg, these vehicles all share a very similar roof drain design that can easily clog and let water into the cabin.

In this video, I show you my process of clearing the rear panoramic roof drains on my Cayenne, a vital maintenance task that’s often overlooked compared to the front drains.

If your rear drains are blocked, you might start noticing water pooling in the spare wheel well, dampness around the rear quarter windows, or visible water tracking down the inside of the C- or D-pillars. These are all red flags that your rear drains need urgent attention.

I start off by showing exactly how to test your rear drains without needing to tear half the car apart. You’ll learn how to open the panoramic roof just enough to access the rear drain channel with a funnel and confirm whether water is exiting properly beneath the car. I also pop off the trim panels to reveal the rubber drain tubes that route water down from the roof to the rear underbody and give them a visual inspection while testing flow.

Fortunately, both of my rear drains were flowing well, but I did find a bit of mud and debris inside exit points where they terminate under the rear of the car. I cleaned these out and followed the common tip of trimming the rubber drain nozzles slightly to prevent future clogs and speed up drainage, especially useful if you park under trees or drive in heavy rain frequently.

This video was part of my effort to track down an intermittent buzzing sound from the amp, which I originally suspected might be caused by water ingress from the panoramic drains. The amp is located just behind the D-pillar—right in the line of fire if the drains overflow—so it made sense to investigate. However, the drain lines were bone dry during testing, and the area showed no signs of leaks, which unfortunately means the buzzing issue lies elsewhere.

At this point, the rear screen washer pipework is my next suspect as its very poor quality. I've previously had issues with water cascading into the boot during rear wash/wipe use, which turned out to be a split in the washer pipe. It's a commonly overlooked source of water ingress in these vehicles, and I’ll be covering that fix in the next video.

Even though I didn’t find the smoking gun I hoped for, I now know my front and rear sunroof drains are all flowing perfectly, and I have peace of mind that they’re not to blame for any cabin leaks.

If you’re chasing moisture issues in your Cayenne or other VAG panoramic-roof vehicle, I’d recommend this as essential preventative maintenance, even if you’re not seeing symptoms yet. Clear your drains a couple of times a year—it’s simple, free, and could save you thousands in electrical repairs down the line.

For more helpful how-to guides and restoration project logs, visit our blog: https://www.spannerrash.com/

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