Everything they told you could be true, especially for a Volkswagen. Most parts must come right from the dealer and they often have to special order them. To add to the confusion, while it's nice that computers detect problems in the circuits and set diagnostic fault codes in memory, for many of the things the computer tests, the results are based on comparing things to other sensors. Just as an example, after the engine has been off for at least six hours, the computer knows the coolant temperature sensor and the intake air temperature sensor had better be reading the same temperature.
When the computer detects a wiring problem to one of those sensors, it knows it can't rely on that one to check the second one, so even if the second sensor fails, there will be no fault code stored for it. It isn't until after the first sensor is replaced and the computer sees it working again that it can resume testing the second sensor. At that point, the second fault code will show up right after the first problem was fixed. That can be real frustrating for mechanics because they don't like having to keep calling you with "more bad news". In this case, it is very likely they had no way of knowing there was a problem with the computer until they corrected other problems first.
It's also true that when a new computer is installed, the software has to be downloaded over an internet connection. That lets them use one computer module to fit a number of car / engine / option combinations instead of dozens of different computers. Once installed, the specific software for that car is installed. The big problem is Volkswagen locks up all their secret information so your mechanic will likely have to take the car to the Volkswagen dealer for that programming to be done, and that is typically VERY expensive. General Motors is equally as bad in that regard and that is one of their many customer-unfriendly business practices that is driving away their repeat customers who have been caught with those high repair costs.
Hyundai allows any independent shop to program any computer on their cars for free. Chrysler and Toyota allow any shop to program any computer other than the Security System for a small charge. Be aware that simply disconnecting the battery on your car or letting it run dead will lead to a very high-cost towing bill and repair bill to have many of the computers "unlocked" at the dealership. There is no valid reason for designing a car like that other than to make money for the dealer and the manufacturer after the sale.
Wednesday, July 6th, 2011 AT 8:37 PM