Erratic turn signal operation can be a result of a failing turn signal flasher relay which will require replacement.
Resources for the Repair and Maintenance of your 2006 Audi TT Quattro
2006 Audi TT Quattro
2006 Audi TT Quattro Problems
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Vacuum leaks, oxygen sensor failure, and catalytic converter efficiency faults can cause the Check Engine Light to illuminate.
An ignition coil or spark plug may fail unexpectedly resulting in an engine misfire and possible illumination of the Check Engine Light.
A creaking type noise may be noted from the front suspension. Replacement of the front sway bar may be required to correct this issue.
The water pump may fail resulting in engine overheating and possible timing belt damage. Overheating and/or timing belt failure can result in very expensive engine repairs. As a precaution, it is recommended to inspect the timing belt and water pump at regular intervals.