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Bizarre electrical issue rear


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The Porsche gods must really hate me right now because my Cayenne is doing all kinds of weird things. The Cayenne was parked outside in the rain last night. I was woken up by its alarm going off. I went outside to investigate. The rear hatch and glass were both unhitched, meaning the actuator motors for each had unlocked without someone actuating them. Now, neither the rear glass nor the hatch open. I could not turn off the alarm. It finally silenced itself. There is no sign of forced entry, so I'm ruling out that. In addition, the brake lights are stuck on no matter if the ignition is on or off. Also, the rear wiper does not work as well as the rear defroster. Shortly after starting the car, I smelled something burning coming from the rear interior. I replaced the battery seven months ago. Help! What is going on?

Edited by 911nick
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i assume you already investigate if there is water somewhere inside your car?! The typical problem under the floor mats driver side / passenger side.

 

No water under the floor mats. There was some moisture on the right rear pillar and some on the rear headliner, but that was likely due to rain entering an open hatch and glass.

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Check the rear comfort control module for water damage or unrelated issue which is not water damage but module or wire harness failure to the module. 

It located behind the CD autochanger. Right side of the boot as you enter the boot hatch behind side trim panels. 

This module controls all the items you mentioned are having faults. 

Replacement of module involves recoding which isn't difficult with vcds or durametric but coding the existing keys to the new/replacement module is a Porsche piwis job apparently, if I could work out how to do key coding with my vcds I would have replaced mine to fix check tail light issue when pressing brake. 

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Check the rear comfort control module for water damage or unrelated issue which is not water damage but module or wire harness failure to the module. 

It located behind the CD autochanger. Right side of the boot as you enter the boot hatch behind side trim panels. 

This module controls all the items you mentioned are having faults. 

Replacement of module involves recoding which isn't difficult with vcds or durametric but coding the existing keys to the new/replacement module is a Porsche piwis job apparently, if I could work out how to do key coding with my vcds I would have replaced mine to fix check tail light issue when pressing brake. 

 

 

Ah, so there is a module for all this stuff. Thanks! Now I have a direction at least.

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I made some great progress today thanks to Mr. Weller. The module was exactly where he said it would be. I opened it up, and sure enough there was a bit of moisture inside along with a destroyed capacitor. I was able to get a used one sold locally.  We will see how it works tomorrow when I install it. I will post results.

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9 hours ago, 911nick said:

I made some great progress today thanks to Mr. Weller. The module was exactly where he said it would be. I opened it up, and sure enough there was a bit of moisture inside along with a destroyed capacitor. I was able to get a used one sold locally.  We will see how it works tomorrow when I install it. I will post results.

No problem at all happy to help. Some pictures of your repair would be fantastic pls. 

Edited by lewisweller
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11 hours ago, 911nick said:

Lewis' diagnosis was spot on. I installed the new box, and everything works like it should! This repair only cost me $50. Lewis, you really saved my bacon. Ekstroemtj, I appreciate your contributions too.

Where did you get the replacement module from and what software did you use to program it? What about programming the keys? 

My check tail light warning is starting to get tiring now, luckily I don't drive much at night. 

It's time I think to spend some more cash and fix this one. 

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Lewis, I found the module on ebay. The item was located within my area. I called the business, and it turned out that the owner lives near me. He was kind enough to delivery it to me that day on his way home. Since it is a used module, it came pre-progamed. How cool is that!

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25 minutes ago, 911nick said:

Lewis, I found the module on ebay. The item was located within my area. I called the business, and it turned out that the owner lives near me. He was kind enough to delivery it to me that day on his way home. Since it is a used module, it came pre-progamed. How cool is that!

Interesting, that means as long as the used module is the same model and spec options wise it's plug and play, great. Also mean the coding for keys is not required then or you wouldn't be up and runny at all. You have keyless entry correct? (kessy)

 

Sorted thanks for the info. 

 

I'm going to find a used module and swap out mine hopefully fix this check tail light bug. 

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