Audi Repair: Dash gear position indication, tiptronic gearbox, transmission control module tcm

Question
Hi. Thanks for looking. I have a 2004 right hand drive A4 Cab, 2.4 V6 with the CVT Tiptronic gearbox. The fault started 1,000km before a 60,000km service was due but I'm pretty sure that was just coincidental. Fault is, after approx 15 minutes of conservative driving [the price of gas makes that necessary :-) ], the auto will change from "Drive" to "Sport" mode all by itself (you notice it as the revs increase from 2000 to 3000rpm) and the gear selection indicator on the bottom of the dash display changes from "D" to "S". For approx 5-10 minutes it does not matter what gear you try to change it to by moving the gear lever into the manual Tiptronic position and trying "up" and "down" or into "S" mode or even "Neutral" and back to "D", the display shows "S" all the time. Stopping and starting off again does not help either. After that period of time it will flicker into "D"  a couple of times then change to "D" for the rest of the drive with no other problems. Once, with lots of mucking about with the gear level, all the segments in the gear display started to flash and it only stopped that after being turned off overnight. The best work-around seems to be leaving it in the manual Tiptronic position, occasionally giving it an "up" or "down" try and just wait for the 10 or so minutes till it comes right. Any idea's of what could possibly be the fault, and does it need an immediate trip to the dealer to put off a major death or just live with it and save heaps of money and get it fixed. The service due is our first outside the excellent 3 year warranty, so we are looking at an estimated cost of $1000 plus just for that but things are a bit tough right now so would love a cheap option.
Thanks for your time. Regards Richard

Answer
Hi Richard,  If all the gears lit up, that would be indicative of a problem with the Transmission Control Module (TCM) or the connection between it and the transmission.  There is an electrical connector that goes into the transmission which is prone to corroding.  I would get this ribbon cable checked first, and see if there are any codes being displayed for the transmission.  It's also worth checking all the connectors, I normally spray some white grease into the connectors to make sure that contacts don't corrode.  Does the problem coincide with weather changes (rain) or any other variations?  Let me know what you find out,  Jan