Phaeton :: Rear Cabin Dome Light Pulled Over Fault Code E327

At the end of my first week of ownership, I encountered problems with the rear cabin light in my car not working properly - sometimes it came on when the doors were opened, and sometimes it did not. I mentioned it to the Phaeton technician at my dealership, and we agreed to just defer investigation and rectification until the car was due to come in for its first oil change.

After I finished putting the start button in, I ran a diagnostic scan on the car, and the problem with the rear cabin dome light was the only remaining fault code. So - I kind of figured "gee, this can't be rocket science to fix", and I removed the rear cabin light assembly from the roof of the car.

I had a close look at it, and found the cause of the problem pretty quickly. When the assembly was put together, the tiny black wire that carries power to the rear cabin interior light button became trapped between the large bus bar that serves as a ground for all the switches and some foam insulation that protects the circuit board from the ground bus bar. The entire assembly would have tested out just fine when it was manufactured, but over time, the vibration encountered in transporting the car from Germany to Canada, and the vibration caused when I drove the car around during my first week of ownership caused the bus bar to cut through the insulation on the wire - hence the short circuit. All I had to do to fix it was just poke the wire out from under the bus bar. Everything works great now.

The fault code that was generated - "Rear Interior Lamp Button - Short to Earth" was absolutely dead-on, and took me directly to the problem. I really doubt if I ever would have found this problem if the car did not have such a competent self-diagnostic system.