A month or so ago I got a convertible roof fault just prior to when the tonneau cover should start to close. manually closed the roof (it wouldn’t move on its own) and checked with VCDS to find “Switch Position / Implausible Signal” figured maybe it was a one-off. I reset the fault and it worked for awhile, then experienced the same problem again. I set off to debug this using the measurement blocks for the top in VCDS - namely the measurements for the Convertible Top Switch status, the Convertible Top Cover Switch status, and the Top Frame Position. I set VCDS to log measurement blocks 1 and 4 while I moved the top down and up.

Naturally, it took several cycles before I finally caught the fault. I treated the status bits as integers and plotted them over time, along with frame position (which was an integer already). In thes plots below, top-down is on the left, top-up is on the right. The “bad” top-down operation is the heavy dotted-red line. I reset it before I put it back up, so the up operation looks like all of the others.

The issue appears to be with the top status since it loses one of its status bits at an odd time (bit 5, if you think of them as 0-7). Plotting all of the status bits for a normal run gives me this, where the top plot is “Readiness” and the following plots are bits 0-7, with frame position overlaid on bit 5 - both of those are in red since I suspect that bit).


Plotting those bits for a failed top-down run gives me this:



Bits 5 and 6 both do something a little odd here, so at this point I’ve decided that I need to replace whatever is responsible for those status bits.

I couldn’t find any description of what the various bits in the status registers meant, so I tried to poke around and figure it out myself. There also isn’t a lot of obvious information about exactly where switches are hidden to monitor top operation, so I looked at lots of assembly drawings in search of switches. In the end, these are my conclusions:



Top Status Bits
0 - Frame Microswitch Assembly- switch towards front, active low
1 - Frame Microswitch Assembly - switch towards rear, active low
2 - Roof Latch open (switch in roof latch housing)
3 - Roof Latch closed (switch in roof latch housing)
4 - Roof Latch closed (switch in latch receiver above windshield)
5 - Potentiometer Related
6 - Potentiometer Related
7 - ???

I don’t know how bits 5 and 6 are determined, but unplugging the frame potentiometer affects them. If either one is set, unplugging returns it to zero. I couldn’t see anything obviously odd about the potentiometer values themselves, but those status bits were behaving oddly so I just replaced the potentiometer. I haven’t seen another roof fault since replacing that potentiometer, so I’m assuming that did the trick.

If anybody else out there is attempting to debug roof status with VCDS, feel free to contact me. I spent a lot of time tinkering with it.