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Hello, I hope someone can help me with a problem on a 2011 S5 Cab
About three weeks ago, my roof failed to go up and I resorted to doing it manually. The next day it worked again. Since then I realised that the roof is failing when the rear driver's side (right) window fails to operate, the seatbelt presenter also fails. When it works or fails is completely intermitted and unpredictable. For example, yesterday I decided to investigate further and removed the rear window internal panel, for about 5 hours, the window was operating successfully and I had the roof down. When I couldn't get any further with my investigation I decided to clear up and put the roof up. Window & Presenter failed, roof failed - roof indicator light flashes 9 times. I decided to go for a drive, testing the window all the time, after about 12 miles - its working again. I parked the car and put the roof up. Left the car for about 15 mins and came back, everything still working. Drove home (12 miles), all still working, checked the car this morning still working. But I know it will fail again!

I have looked at the SSP_960193 guide for the Cabriolet, and it shows the rear windows controller managing the window and the seat belt presenter. This module J389 uses LIN bus comms with the front door module J387 acting as the master connected to CAN. I was hoping to monitor (with an oscilloscope) the LIN input to the J389 module and see if comms is being attempted when the system is failing. I have examined the wiring harness into the door, as the controller is daisy chained from the front controller and I thought a wire might have fractured. However all looks good. Also the intermittent behaviour doesn't see consistent with a broken wire.
I don't have the ability to read diagnostic codes, do I purchase a device or do I just leave the whole thing to a garage? It concerns me that with an intermittent fault they could take ages to diagnose, and the bill could be big!

Some questions:
  • Has anyone experience this type of intermittent fault?
  • Where is the J389 module? It's not behind the rear window panel or under the rear seat which is what the SSP_960193 guide indicates.
    • It's possible it's in the rear quarter accessed through the boot. What's the official number on the device?
  • Any Idea what the problem could be?
  • Will a Ross Tech Hex2 diagnostic help me tract the fault? Or are there alternatives?
Here's hoping for a solution.
Many thanks
 

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2009 (MY2010) S5 + APR Stage1
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56 Posts
I'm in South Manchester and would be happy to plug my VCDS in to see if we can find any errors. Are you local?
 
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