Audi TT TTweakers Guide

This guide is about tweaking and troubleshooting the original Audi TT, also known as mk.I. The information is snatched from various sources, mostly from Audi related forums on the Internet. Even tough the information is believed to be correct, it is provided with no warranty of any kind.
The guide is divided into three parts. First part, Chapter 2, contains information how to troubleshoot common problems, and some general information. Second part, Chapter 3, contains instructions for tweaking various features. Third part, Chapter 4, is a collection of lists and tables, in an easily printable form.
As most things in a car are nowadays controlled with diagnostics software and a computer, this guide is mostly about the tricks and tweaks that can be done purely with software. At the moment, no hardware mods are included, though some general information is provided.
This guide is not supposed to replace the workshop repair manual, but rather provide some often used information in easily accessible form. If you ever have read the repair manual, you probably appreciate it…
Courtesy of factory repair manual
A Diagnostic Trouble Code (DTC) is a fault code stored in the car’s computer system. DTCs can be retrieved with VW/Audi Factory Scan Tools such as the VAG 1551 or VAG 1552 through a diagnostics connector (OBD-II). Several aftermarket scan tools and computer programs, like VAG-COM, are also capable of retrieving this information in this factory mode. The factory mode also allows the scan tool to be used for system diagnostic functions and also parameter tweaking.
Some DTC information can also be retrieved in a generic mode. The generic mode is not as complete as the factory mode, but allows commercially available scan tools to be used simply to read DTCs. For example, MOT stations can use the generic mode to retrieve some basic information about the engine’s fundamental functions. A DTC consists of five digits, having the following structure.

pdf source: http://www.wikitt.org/wikiTT/images/f/fc/TTweakers-Guide.pdf