Interpreting car codes- what do I need?

[Rick Liotta]

Hello all----



I have a 99 A4 Quattro and its yellow 'check engine' light just came on at 
about 75500 miles (maybe a little less miles).  The car is running fine.



I would like to know how to interface with the car's brain.



Please-- what do I need to access and interpret any codes that are car is 
giving-- software? Interface cable?



Thx very much!



Rick-in Anchorage.