The vehicle has switched on the particle filter light. After regeneration the light goes out but the engine light remains on

SYSTEM DESCRIPTION: The particle filter removes residual carbon particles from exhaust gases. The particle filter consists of a microporous structure with channels arranged to filter the exhaust gases.
The drainage pipe consists of several elements:
- an oxidation catalyst located downstream of the turbocharger: This catalyst enables
reach the HC/CO levels of the regulations in force and generate an exothermic effect (raising of the exhaust temperature through a catalysis phenomenon) necessary for regeneration of the particulate filter,
- a catalytic particle filter positioned under the bodyshell,
- differential pressure sensor to provide the calculator with the values of the pressures upstream and downstream of the particle filter,
- a temperature sensor upstream and downstream of the particle filter,
- a temperature sensor upstream of the turbine (TAVT)

When the vehicle is in motion, the particle filter is loaded with particles (soot). Based on a given soot mass, determined by means of coded curves in the computer, the regeneration mode can be activated if the maximum soot mass in the particle filter is reached and if all engine operating conditions (coolant temperature, etc.) are met.
Regeneration of the particulate filter consists of burning off the soot particles accumulated in the filter.
The differential pressure sensor measures the inlet/outlet differential pressure of the particle filter. This measurement allows the mass of soot in the particle filter to be estimated by means of curves encoded in the calculator:
(soot mass = differential pressure as a function of exhaust volume flow).
If all criteria are met, the computer switches to regeneration mode. The injection strategy is then modified in order to raise the exhaust temperature to between 550˚C and 650˚C.

This temperature will allow the particles accumulated in the filter to be partially or fully burnt (regenerated). Regeneration effectiveness depends on the particle filter inlet temperature and the time spent in regeneration mode.
Regeneration can be performed automatically while driving if:
- the soot mass is below the threshold for applying the error "DF308 Particle filter clogged'..
- the number of failed regenerations while driving is below the error threshold '.DF311 Number of failed regenerations exceeded“.

FAULT ANALYSIS:

With the help of the self-diagnosis tool, the following errors are detected in the engine control unit:

• P2002= Particulate Filter;
• P1435= Particle Filter Regeneration

Both errors cannot be deleted.

Since regeneration seems to have been successful and the filter failure light has gone out, an analysis of the system's operating parameters is carried out:

• Filter temperature: consistent value
• Differential pressure: detected a value between 10-20 mbar at engine idle. So the value confirms that the filter is clean.
• Diesel level: 1/3 tank
• Absence of other errors in self-diagnosis.

Once it has been verified that there are no apparent faults that could lead to the filter not being completely clean, the command 'replace particle filter' is launched, as error P2002 refers to an excessive accumulation of particles inside the filter. Therefore the particle filter must be replaced.

With the help of the self-diagnosis tool, the specific adjustment is carried out: "Cancel Particle Filter Data“.

Once the adjustment is launched, the errors are then removed from the computer and the engine light is switched off.

CONCLUSIONS:

The fault was caused by the delay with which the customer took the car to the garage after the DPF warning light came on. 

In the absence of regeneration, with an already dirty filter, continued driving caused the filter to become completely soiled, which resulted in replacement.

If the customer had taken the car to the workshop immediately, it would have been sufficient to regenerate the filter.

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