2 litre TDI fan running fast after switching off

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This one has created alarm to a number of new people with a 2.0 TDI engine who are new to this process. The car uses either passive or active DPF regeneration to clean the filter. There is no dashboard light to tell you when either of these processes is running. A tell tailsign of passive regeneration is when the car in DSG form changes gear for no apparent reason. Generally this can be noticed after completing regeneration and reducing the revs.

The active regeneration is when fuel is used in the process and temperatures are increased. In stopping the car the fans run at full speed to cool the engine off. On a new car heat and smell can be created when the car is at rest. The smell seems less noticeable once the cars been run in. Heat discipating by the fans is the same.

The process active / passive takes place around every 200 miles or so, back pressure in the exhaust is also monitored. Honest John has a VAG piece on this together with information on longevity and treatment processes.

https://www.honestjohn.co.uk/faq/diesel-particulate-filters/
 
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