If you are having problems with the Tiptronic activating, please consider reading this before spending money to have someone repair it. The Tiptronic system seems to rely on magnetic sensors to do its work. It is even debatable whether or not the shift level movements actually do anything else besides moving a magnet within a sensor network. I could find no mechanical linkages or the sort when the lever was moved into Tiptronic. In fact, the lever disengages from the traditional shifting system when it is moved to the right. It seems the resistance during +/- shifting is artifically created by spring to simulate 'work' being done.
Here's the story:
My car (99 A6) was broken into the other day and the glass that shattered entered into the shifter assembly, eventually disrupting the functioning of the Tiptronic system.
I could still shift between all other gears and physically get the shift lever to enter into the Tiptronic selector, but the transmission simply remained in "D" Drive mode regardless of + / - shifter movement. This was confirmed with the dash console display.
I took apart the shifter plate and surrounding trim to expose the internals. The magnet as we have been familiar with (the one housed on the rubber boot to the left of the shift lever originally described by Boston Diver) was intact and was being read by the componentry as indicated by illuminating gear selection readouts (P R N D, etc) on the bezel.
However, as previously mentioned, when the lever is physically shifted into 'Tiptronic Mode' the 'D' is still illuminated and the +/- indicators are dim. On a working system, the 'D' should become dim while the +/- LED's become brighter. Conclusionn: Another sensor was not being triggered.
It turns out there's ANOTHER magnet that was never mentioned and a set of sensors that read the magnet when the Tiptronic is engaged. This magnet is not only responsible for enabling Tiptronic but also for 'sensing' upshifting/downshifting. When the shift lever is moved to the right, the magnet slides along with the motion of the lever and engages three sensors on the underside of the bezel (see picture).
Image courtesy of Boston Driver (thanks BD!)
Within the circled portion you can see a sliver of a metallic object sitting within a plastic sleeve. That plastic assembly moves rightward toward the passenger when the shifter is moved into Tiptronic Mode. It then engages three sensors and when moved up or down, signals the componentry to act accordingly.
Here are the three small magnetic sensors on the underside of the chrome bezel. This silicon chipset can be seperated from the bezel.
It took me considerable time to figure this out as the plastic that housed the magnet broke off and sent the magnet elsewhere. I used another magnet to see if moving it near other parts of the silicon board would trigger the +/- LED to illuminate, with the knowledge that the magnet on the 'boot' was responsible for illuminating the (P R N D 4 3 2) LED's on the bezel. It worked, and I realized I had a missing magnet. After much searching I found it sticking to a piece of the metal frame underneath some shift linkages. Besides the fact that it was broken (very difficult to join a magnet that is broken as they repel each other), I had to tape it back since the plastic sleeve it settled in was in pieces. Hopefully it holds.
The orientation of the magnet to the sensors is critical for both magnets. If you flip them upside down, the sensors won't read them. Also, the magnet that actuates the tiptronic is long and seems to trigger the center sensor at all times regardless of placement, and during shifting triggers a combination of either the top + middle or bottom + middle. Shifting cannot be completed without this combination, so if you lose the magnet, you need to find something just as long (but not longer, since even a slight increase in length will have all three sensors being triggered at rest). Also, I tried one of those weak flexible refrigerator magnets commonly used as ads for local pizzerias - they do not work. A sufficiently strong magnetic source is required. I did not test whether the magnet on the rubber boot was required in combination with the 'secondary' magnet in order to get the Tiptronic working, but I imagine it would. Though even without that magnet, just by waiving another magnet near the Tiptronic sensors, I could get the +/- lights to illuminate on the bezel. Also even with 'D' illuminated, when the other sensors detect a magnetic source, it overrides the signal from the magnet on the boot and highlights the +/- LED's.
That's it for now. Hope it can help someone in the future.
BTW My Tiptronic is back in action.