Shown in the overview below are the components of the diesel particulate filter system.

  1. Control unit in dash panel insert J285
  2. Engine control unit
  3. Air mass meter
  4. Diesel engine
  5. Temperature sender before turbocharger G507
  6. Turbocharger
  7. Temperature sender before particulate filter G506
  8. Lambda probe G39
  9. Particulate filter
  10. Exhaust gas pressure sensor 1 G450
  11. Temperature sender after particulate filter G527
  12. Silencer
The overview shows a system with single exhaust pipe. On multi-pipe exhaust systems the particulate filter and the sensors on the exhaust system are installed for each set of cylinders.

The particle filter

The catalytic coated diesel particulate filter is located in the exhaust system after the turbocharger, within close proximity of the engine. Two components, the oxidisation catalyst and the particulate filter, have been combined to form one unit, the catalytic coated diesel particulate filter. It joins the functions of the oxidisation catalyst and the diesel particulate filter in one single component.





As a diesel particulate filter it filters out the carbon soot particles from the exhaust gas. In its function as oxidisation catalyst, it cleans the exhaust gas of hydrocarbons (HC) and carbon monoxide (CO). They are converted into water (H2O) and carbon dioxide (CO2).

Detailed information about oxidisation catalysts can be found in self-study programme no. 124 "Diesel engine catalysts"


Diesel particulate filter warning lamp V231

The diesel particulate filter warning lamp can be found in the dash panel insert. It lights up if the diesel particulate filter is subject to many short journeys, thus preventing regeneration.




If the vehicle is driven frequently over short distances, regeneration of the diesel particulate filter can be impaired because the exhaust gas temperature does not reach the necessary level. Since regeneration cannot take place, there is a risk of the filter becoming damaged or blocked by carbon soot deposits. In order to avoid this, the diesel particulate filter warning lamp lights up in the dash panel insert if the carbon soot level reaches a certain threshold.

With this signal, the driver is requested to drive at more than 60km/h at a constant rate for a period of about 15 minutes. The filter can be cleaned most effectively if the vehicle is driven in 4th or 5th gear in a speed range of approximately 2000 rpm. The warning lamp must go out after this measure.

If the diesel particulate filter warning lamp does not go out after this measure, the preglow period warning lamp will light up and a message will be displayed in the dash panel insert saying "Engine damage - workshop" (or words to that effect). This informs the driver that the vehicle must be driven to the next workshop.

The precise details about how to drive the vehicle when the diesel particulate filter warning lamp lights up can be found in the operating instructions of the vehicle! In any case, the traffic regulations and speed limits must always be adhered to! 
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