Clogged DPF filter – how to read errors (P2002, P242F, etc.) and correctly diagnose the particulate filter

The diesel particulate filter (DPF/FAP) is a key component of modern diesel engines, essential for meeting stringent emission standards. Its primary function is to capture harmful soot particles, but a faulty or clogged DPF is often only a symptom of deeper engine problems , not the cause itself.

A clogged exhaust system, even by 10-15%, places a significant strain on the engine. This results in reduced power, increased fuel consumption, and accelerated wear of other components. Proper DPF diagnosis requires analysis not only of the filter itself, but also of the entire engine ecosystem – from the injection system, through the intake, to the ancillary systems (EGR, turbo, SCR/AdBlue).

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What is a DPF filter and how does it work?

DPF (Diesel Particulate Filter) is a particulate filter used in diesel cars, whose purpose is to reduce the emission of harmful particulate matter (PM) into the environment.

The DPF filter traps particulate matter generated during diesel fuel combustion and stores it within its structure. The accumulated soot is periodically removed through a thermal process called regeneration . The filter is heated to high temperatures, burning the soot particles and turning them into ash.

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Common DPF errors – what do typical codes (P2002, P242F etc.) mean?

Diesel particulate filter (DPF) faults generate numerous DTCs. Below are the most common errors, along with a brief description, to help answer the question , "What does a DPF error mean on a diagnostic computer?"

1. Errors indicating DPF blockage

• P242F – excess soot in the DPF filter.

• P2002 – DPF filter efficiency too low (Bank 1).

• P2003 – DPF filter efficiency too low (Bank 2).

2. Errors related to DPF regeneration

• P244A – DPF regeneration system efficiency (Bank 1) – too low.

• P244B – DPF regeneration system efficiency (Bank 1) – too high.

• P2458 – DPF regeneration takes too long.

• P2459 – DPF regeneration too frequent.

3. Differential pressure sensor errors

• P2452 – DPF differential pressure sensor problem – low signal.

• P2453 – DPF differential pressure sensor problem – high signal.

• P2454 – DPF differential pressure sensor – low input.

• P2455 – DPF differential pressure sensor – high input signal.

4. Exhaust gas temperature sensor errors

• P0544 – Exhaust gas temperature sensor problem (Bank 1, sensor 1).

• P0546 – ​​exhaust gas temperature sensor – high signal.

• P2031 – problem with exhaust gas temperature sensor (before DPF).

• P2033 – problem with exhaust gas temperature sensor (after DPF).

5. Fuel/AdBlue quality errors affecting DPF

• P229F – NOx sensor problem (affecting DPF efficiency).

• P20EE – insufficient efficiency of the NOx reduction system – impact on DPF.

• P207F – Incorrect AdBlue quality – may affect DPF regeneration.

6. General errors related to the DPF system

• P141F – DPF filter function problem – emission limit exceeded.

• P2463 – DPF soot level too high.

• P246C – Differential pressure sensor indicates a problem with DPF performance.

• P24A4 – problem with reading the pressure difference or temperature in the DPF system.

7. Errors with cooperating systems that "damage" the DPF

• P0299 – insufficient turbocharger boost – impact on DPF efficiency.

• P0101 – problem with the air flow sensor (MAF) – DPF regeneration disturbances.

• P0401 – too low flow in the EGR system – affecting the DPF load.

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I. DPF system and diagnostic tools – how to start DPF diagnostics?

Always start the diesel particulate filter diagnostics by connecting a diagnostic computer (VCDS, Thinkcar, Autoxscan and others) in order to:

• reading error codes (DTC),

• verification of real parameters (live data / real values).

DPF error codes alone are not enough. It's necessary to check what values ​​the engine control unit (ECU) is seeing from key sensors.

Key DPF monitoring sensors

The engine control computer (ECU) calculates the filter saturation level using data from three main sources:

1. Differential Pressure Sensor
   This is the most important sensor that directly indicates the degree of filter clogging.

   • It measures the exhaust gas pressure before the filter and compares it with the pressure after the filter or atmospheric pressure.

   • If the exhaust pipes leading to the sensor are clogged or leaking, the measurement is false and the ECU may incorrectly assess the DPF condition.

2. Mass Air Flow Sensor (MAF)
   The controller assumes that the amount of air drawn in by the engine (measured by the MAF) is equal to the amount of exhaust gases expelled into the exhaust system.

   • Erroneous readings from the MAF (wear, contamination, intake leaks) lead to incorrect calculation of the soot mass.

3. Exhaust Gas Temperature (EGT) Sensors
   Data on the exhaust gas temperature are needed to calculate its density, and therefore the exhaust gas flow, and to correctly calculate the amount of soot.

   • Temperatures are key during active regeneration, which requires reaching approximately 600–650°C .

   • EGT sensors can be inaccurate (e.g. by 5–8°C on a cold engine, or even by 100°C at high temperatures), but this does not always result in an error.

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II. Interpretation of key DPF diagnostic parameters

DPF diagnosis involves checking actual values ​​in dedicated measurement groups. These allow us to determine whether the filter is clogged, faulty, or the problem lies with the engine.

1. Differential exhaust pressure (pressure difference across DPF)

This is the most important and direct indicator of filter condition.

• At idle

  • Correct value: approx. 5–7 mbar (hPa) .

  • A value of 10–12 mbar (hPa) – considered elevated/average.

  • A value above 14 mbar is a clear warning signal.

• Under load (dynamic driving)

  • The measurement should be taken during full acceleration (e.g. in 4th gear).

  • The pressure should not exceed 300 mbar .

  • Exceeding 400–450 mbar activates limiters in the engine control unit, which cut the fuel dose to protect the engine – the driver does not always immediately feel the power drop.

2. Soot mass (calculated and measured)

The ECU tracks both:

• soot mass calculated – based on algorithms (driving style, fuel consumption),

• measured soot mass – corrected mainly on the basis of the pressure difference sensor.

Typical threshold values:

• Many vehicles initiate active regeneration when the DPF fills to approximately 21–24 g of soot .

3. Ash Mass

Ash (metal oxides, oil combustion residues) accumulates permanently in the filter and is not removed during regeneration . Its amount:

• is calculated based on engine wear and should correlate with mileage,

• in the VAG group it is assumed that Audi predicts the DPF lifespan to be approximately 240,000 km , with a maximum ash mass of approximately 80 g .

Note: Resetting this parameter ("filter replacement" in the tester) without actually replacing the DPF is an error. The ECU "thinks" it has a new filter, which disrupts the soot and wear calculation algorithm.

4. Regeneration frequency

A functioning DPF system should regenerate itself in normal operation:

• every 600–800 km – ideal values,

• 300–400 km – still acceptable, especially in mixed use (city/highway).

Problems begin when:

• regeneration occurs every 150–200 km – a signal of a serious problem with the engine or accessories,

• Too frequent regeneration (especially below 300 km) leads to:

  • dilution of engine oil with unburned fuel (exhaust injection),

  • increasing the oil level and impairing its lubricating properties.

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III. The source of the problem – what really causes DPF clogging?

The DPF filter is the final component of the exhaust system. In practice, clogging is a consequence of engine or accessory problems, not the cause.

A. Injection faults and oil problems

Improper combustion of the mixture (excessive smoke, large amounts of soot) is the main culprit of a clogged filter.

• Leaking fuel injectors

  • The injector nozzles, despite correct adjustments at idle, may not atomize the fuel correctly under full load.

  • This generates a large amount of soot and ash and can lead to overheating.

  • Injection corrections usually only work up to approximately 2000 rpm .

• Engine wear

  • Blow-by and worn piston rings cause oil mist and oil to enter the combustion chamber through the pneumatic valve.

  • Burning oil creates a large amount of particulate matter and ash, which quickly clogs the DPF.

• Intake contamination

  • The exhaust gases from the EGR mix with the oil mist from the pneumatic valve, creating carbon deposits in the intake manifold.

  • A clogged intake manifold and carbon deposits on the valve stems interfere with the filling of the cylinder with air, which worsens combustion and increases soot production.

B. Faults in equipment and ecological systems

The exhaust gas cleaning equipment can also break down, directly putting a strain on the DPF.

• Leaking AdBlue injector (SCR)

  • Urea (AdBlue) leaking into the exhaust crystallizes, creating white streaks and deposits in the DPF.

  • This physically blocks the exhaust flow and increases the differential pressure.

• EGR problems

  • A sticking EGR valve (e.g. in the open position) causes smoke, loss of power and starting problems.

  • Too active EGR increases the amount of soot.

  • Improper operation of the EGR cooler may prevent the engine from reaching the temperatures required for regeneration.

• Turbocharger undercharging/overcharging

  • Boost pressure deviations of 100-200 mbar (under- or over-boost) may not generate an error code (especially in Audi/VW/Mercedes), but they do disturb the air-fuel ratio.

  • The result is excessive soot production.

  • In biturbo engines, a common problem is deformed flaps in the turbine geometry.

• Cooling system faults

  • Too low a coolant temperature (e.g. a faulty thermostat) prevents the minimum operating temperature from being reached – often around 81°C .

  • This blocks the ability to start the DPF burnout procedure.

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Common Causes of DPF Errors – Quick Summary

DPF filter blockage:

• short driving distances, no possibility of full regeneration,

• excessive soot due to a faulty injection system or turbocharger.

Sensor malfunction:

• damaged differential pressure sensor,

• damaged exhaust gas temperature sensor.

Abnormal regeneration:

• contaminated intake system,

• faulty fuel injectors.

Fuel/AdBlue problem:

• poor fuel quality,

• low quality AdBlue in vehicles with SCR system.

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DPF diagnostics in practice – what parameters should be checked on the computer?

When diagnosing a clogged particulate filter, first check:

• differential pressure on the DPF filter – read by the so-called "differential gauge",

• DPF back pressure – especially in BMW cars,

• temperatures on the DPF filter ,

• calculated mass of soot and ash .

The limit values ​​may vary for each car, so it is worth:

• monitor the normal operating conditions of your DPF on an ongoing basis,

• use dedicated applications or universal diagnostic testers such as SDprog .

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Summary – how to approach the diagnosis of a clogged DPF?

Diagnosing a clogged DPF requires a holistic approach . Mechanics should routinely:

• check key DPF parameters (especially exhaust gas differential pressure under full load),

• analyze data even when the car is not yet reporting errors on the dashboard.

In practice, very often:

• the problem is not the filter itself, but the disturbance of the air flow (MAF),

• incorrect operation of injectors,

• AdBlue, EGR or turbocharger system faults.

These causes must be removed before we can repair the effect of a clogged DPF filter.

Prevention is crucial to the life of the filter and engine:

• regular cleaning of the intake,

• frequent oil changes with appropriate quality,

• checking engine and DPF operating parameters using a diagnostic computer.

This allows you to significantly extend the life of the DPF, reduce the number of regenerations, and thus reduce the risk of expensive repairs related to the exhaust system and engine accessories.