Catalytic converter
Applies to Audi A6s with petrol engine: The Audi A6 must only be used with unleaded petrol; otherwise the catalytic converter will be irreparably damaged.
Never allow the fuel tank to run completely dry, as the irregular supply of fuel can cause misfiring. This allows unburnt fuel to enter the exhaust system, which can cause overheating and damage to the catalytic converter.
Diesel particulate filter
Applies to Audi A6s with diesel engine: The diesel particulate filter can filter out almost all soot particles contained in the exhaust gas. In normal driving conditions the filter is self-cleaning. Should the self-cleaning function of the filter not be able to operate, e.g. when the Audi A6 is continuously used only for short trips, the filter becomes obstructed with soot and the indicator lamp 
for the diesel particulate filter lights up ►Link.
for the diesel particulate filter lights up ►Link.WARNING!
The exhaust system is very hot when the Audi A6 is being driven and after the engine has been switched off.
- Never touch the tailpipes when they are hot – risk of burns!
- Because of the high temperatures which can occur in the emission control system (catalytic converter or diesel particulate filter), do not park the Audi A6 where the exhaust can come into contact with flammable materials under the car (e.g. on grass or at the forest edge) – risk of fire!
- Do not apply any underseal agents in the area around the exhaust system - risk of fire!