Audi Repair: Audi A6 quattro 1998, audi a6 quattro, diagnostic check

Question
there is a warning light that comes on when you start the car and looks like an exclamation mark in a red circle, audi have advised they will need to do a diagnostic check but this will cost over £100.00, can you advise what this warning light means and how to fix it or switch it off??

Answer
Wll here in the US you can get the fault codes read out for free at Autozone.  However in the UK I would buy a VAG-COM (ebay or other on-line stores) and read the codes out, after you buy the VAG-COM and read out the codes you will still not have spent $200 (or 100GBP)  and you will have the diagnostic tool to rent to your friends and use the next time you need it.  The red exclamation mark does indicate a serious problem though, and it does need to be checked immediately.  I would check all the fluid levels first, especially brake fluid.  Let me know,   Jan