Catalytic converter
Applies to vehicles with petrol engine: The vehicle must only be used with unleaded petrol; otherwise the catalytic converter will be irreparably damaged.
Never run the tank completely dry. The irregular fuel supply can cause misfiring, which would allow unburnt fuel to enter the exhaust system, which could cause overheating and damage the catalytic converter.
Diesel particulate filter
Applies to vehicles 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 vehicle 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!
- Because of the high temperatures which can occur in the emission control system (catalytic converter or diesel particulate filter), do not park the vehicle where the exhaust can come into contact with flammable materials under the car (e.g. on grass or at the forest edge). - Fire hazard!
- Do not apply any underseal agents in the area around the exhaust system - fire hazard!