dscottjr

to do that at goapr.com. If you have an american box - 2000 would be A for a 6-speed or B for a Tiptronic - or if you have a europe box - don't know what the europe 02 box p/n is but i could find it. Look at it and post the results - interested to know what box you have. Here's the link to the how-to BTW<ul><li><a href="http://www.goapr.com/Audi/support/ecu_a4_s4_a6_late.pdf">http://www.goapr.com/Audi/support/ecu_a4_s4_a6_late.pdf</a</li></ul>

WindyCityS4

If you do not get the spare ecu, you need to send your ecu to the tuner and wait for it to be returned. If you are using a US tuner, this means at least 4 days that you cannot use your car. Another advantage is if the car is acting up, you can go back to stock and see if it is the chip or something else.
What is the above worth to you? If it is not worth $600 USD (the cost of a spare ECU), then don't get the extra ECU.

Cost savings is the advantage to chipping your stock ecu. (unless you do not have access to a VAG--there are special things you need to do to a new ECU with the VAG. Otherwise you loose cruise and other functionality)

M3iRiSH

There are 4 code variations for 3 years of 6-speed cars alone.
All it takes is one different sensor to change the code. I can imagine there are a lot of emissions differences between our cars.

Did you check your ECU numbers? I doubt it, but why not 8^ )