DPF Diesel Particulate Filter and re-generation


Diesel Particulate filters (DPF) or 'traps' do just that, they catch bits of soot in the exhaust. As with any filter they have to be emptied regularly to maintain performance. For a DPF this process is called 'regeneration' – the collected soot is burnt off at high temperatures of around (600°c) to leave only a tiny ash residue.

DPF Structure
DPF components
DPF pressure sensor

The differential pressure sensor is used by the DPF software to monitor the condition of the DPF. Two pipe connections on the sensor are connected by pipes to the inlet and outlet ends of the DPF. The pipes allow the sensor to measure the inlet and outlet pressure of the DPF.

The Differential pressure sensor will have a reference voltage of approx 5V and a signal voltage of approx 0.5V to 4.5V

As the amount of soot trapped by the DPF increases the the pressure on the inlet side of the DPF will also increase.

Differential pressure sensor measures exhaust pressure pre and post DPF


A relatively clean DPF will return a voltage of approximately 0.5V. This rises to approximately 4.5V for a full DPF

If the differential pressure sensor returns a voltage of 4.5V or more to the ECM, and if all other conditions are met, Regeneration of the DPF will take place.

Exhaust temperature sensors

Upstream temp sensor

The upstream temp sensor will be located somewhere between the turbo and the catalytic converter and informs the ECM of the temperature of the exhaust gases after they have passed through the turbo upstream of the catalytic converter


You may at times see some radical temperature sensor readings of approx-3500°c while using Bosch actual data.

This type of reading will be a default setting of the ECM as an open circuit of the temp sensor. With this type of reading the Regeneration phase will not be able to take place.

A good starting point before attempting a Regeneration is to check the temp sensor readings as you could be waisting time.
T1-T2-T3 temp sensors

Some manufacturers can have upto 4 exhaust temperature sensors

A different way of heating the DPF to burn off the soot using an electric heater system
On some vehicles a Vaporizer is used. This injects diesel into the exhaust upstream of the DPF And incorporates a glow plug to ignite the fuel to allow the temperature to reach the (600°c) mark to burn the soot

You will notice some DPF's will be close to the engine and some will be further away on the exhaust system and will have a different set up but the Regeneration process is the same

There are two DPF cycles: passive and active.
Passive Regeneration
Passive Regeneration

Passive regeneration takes place automatically on motorway-type runs when the exhaust temperature is high. Many cars don't get this sort of use though so manufacturers have to design-in 'active' regeneration where the engine management computer (ECU) takes control of the process.

On passive cycle the DPF will require the car to regularly be driven significant distances at relativey steady revs of 1,750rpm to 2,500rpm for the DPF to get hot enough to regenerate and burn off the particulates in it.

Active Regeneration
Active Regeneration

Active Regeneration occurs when the level of soot in the filter reaches around 45%. The ECU makes small adjustments to the fuel injection timing and increases the exhaust gas temperature. This increases the exhaust temperature which then initiates the regeneration process, burning away the soot trapped in the DPF.

Forced Regeneration

Using Bosch Diagnostics select the correct engine code for the Ecu to communicate correctly

A little tip!!!

You may need to select a different model year or manually select a different engine code to get full functions of the ecu.

Select DPF Regeneration in Roadside tasks or select Adjustment and Settings or adaptions in the engine ecu

Follow all on screen prompts

You may have all these warning lights on the display
Time to regen the DPF
Read the info
Proceed to continue
Flick up to start the Regeneration phase and increase the RPM
Most vehicles will have a slightly different holding revs for the Regeneration process
Static Regeneration in progress showing around 1500 RPM

The glow plug light may flash while performing a static regen of the DPF

It is very important to monitor the exhaust gas temperature

Watch the exhaust gas temperature.

You should expect to see around (600°c) on one of them within 15 minutes of the Regeneration phase.

On most vehicles you can be looking at a time scale of around 40 minutes to carry out a successful Regeneration.

If after 15 minutes and you are not seeing the exhaust temperature of around (600°c) then abort the process as you will be waisting time.

If this should happen then the best course of action would be to reset the DPF adaptions and then advise to go straight to there garage for further checks

Once reset this can allow the vehicle to be driven to the garage for further checks

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Created By
Dave Harvey

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