The DPF or diesel particulate filter is a device fitted as standard to all diesel vehicles after 2009. Its purpose is to filter out and collect harmful soot particles from the engines exhaust gasses. They are stored in the filter and the level of stored soot is monitors by the vehicles engine control unit or ECU. When the filter reaches its fill level the ECM will initiate a process called regeneration. 

 The regeneration process will increase the temperature in the DPF to as high as 650/700 degrees in order to incinerate the soot particles, reducing them to micro particles before allowing them to exit the exhaust. 

 For this process to be successful, the ECU will need to closely monitor all activity both from the engine and the DPF. To do this it employs many sensors both on the engine and the DFP to feed back accurate information. If a fault exists on these sensor and the ECU is aware, It may holt any regeneration process from starting. If a mechanical fault exists causing incomplete combustion of air fuel mixture, this may also affect the DPF by filling it to quickly and causing to frequent regenerations.

For the regeneration process to start the ECU will need certain conditions to be met. On of the more common causes of blocked DPF’s is due to driver usage. The ECM needs to see in most cases that the engine is fault free, has adequate fuel levels (Normally more that a quarter of a tank) and is up to full working temperature. It is comment for these vehicle to be used only for short journeys which in turn does not allow time for the Engine and DPF to get up to the correct working temperature. 

 This can over load the filter to a point where the ECU recognises that the fill level is above its maximum safe level for regeneration, when this happens it is common for the ECU to put a warning light on the dash alerting them of the issue and also reduces engine power to limit further loading of the DPF.

 This is when the vehicle is often brough to a garage for repair. It is quite common unfortunately for a garage to clean or even replace the DPF at this point without diagnosing the root cause of the DPF blocking. If this happens the customer will collect the vehicle and it will drive fine, however as the fault still exists the DPF will block again and the problem will return quickly. 

 It is very unlikely that the actual DPF is the root cause of the issue, and in most cases it’s just a symptom of another issue that exists. For example If a temperature sensor fitted to the DPF itself is faulty and is not allowing the ECU to monitor the regeneration, the ECU will not be able to safely control the regeneration temperature, so in turn it will not regenerate and the DPF will be over loaded in time and block. If a garage just cleans or replaces the DPF but not the sensor then the problem still exists and the DPF will block again.

 It is therefore very important that anyone fixing these systems fully understands how they work and is able to correctly diagnoses the root cause. As Diagnostic specialists we are able to accurately diagnose and repair both blocked DPF’s and determine the root cause, preventing the fault from returning.