Causes, Symptoms, Repair, and Safe Cleaning

The DPF filter (Diesel Particulate Filter) is one of the most important components of the exhaust system in diesel cars. Its job is to capture soot particles generated during diesel combustion. Unfortunately, over time it can become clogged—especially in vehicles used mainly in the city. In this article, you’ll learn why the DPF filter gets clogged, how to recognize the first symptoms, what diagnostics look like, and how to clean it safely or prevent the issue from returning.

Ceramic honeycomb structure of a DPF filter – cross-section
DPF filter – the ceramic honeycomb substrate traps soot particles from the exhaust system.

Table of Contents

  1. Most common causes of DPF clogging
  2. Symptoms of a clogged DPF filter
  3. Quick diagnostics and measurements
  4. How to clean a clogged DPF
  5. How to prevent DPF clogging

Most common causes of DPF clogging

The DPF clogs when conditions for automatic regeneration are not met or when other engine faults increase soot production. Here are the main reasons a DPF stops working properly:

  • Short-distance driving – the engine never reaches operating temperature, so regeneration is interrupted.
  • Faulty thermostat – coolant temperature is too low to burn off soot.
  • Faulty differential-pressure or exhaust-temperature sensors – the ECU does not trigger regeneration at the right time.
  • Dirty intake system and EGR valve – more soot enters the system than the filter can capture.
  • Worn injectors or turbo – cause excessive smoke and soot buildup in the DPF.
  • Poor-quality fuel or oil without a Low-SAPS spec – ash accumulates in the filter and cannot be burned off.

As a result, the filter clogs more and more, which shows up as power loss, higher fuel consumption, and the DPF warning light.

Symptoms of a clogged DPF filter

Early detection helps avoid costly repairs. Look for these signs that your DPF may be clogged:

  • DPF warning light or “Check Anti-Pollution / DPF Full” message.
  • Noticeable power loss and entering limp mode.
  • Increased fuel consumption – often 0.3–0.5 gal/100 mi (1–2 L/100 km) more.
  • Frequent, unsuccessful automatic regeneration attempts.
  • Unstable idle, burning smell, and smoke when accelerating.

Ignoring these symptoms can damage the turbocharger, injectors, and even the filter itself – replacement can cost thousands of PLN.

Quick diagnostics and measurements

Before deciding on cleaning or replacing the DPF, perform basic diagnostics. You can do it yourself or at a shop with a diagnostic scanner.

  1. Read OBD trouble codes – e.g., P2002, P2452, or P2453. These indicate problems with the filter or sensors.
  2. Check engine operating temperature – it should reach 85–95°C (185–203°F). If it’s lower, the thermostat may be at fault.
  3. Measure differential pressure across the DPF. A high value at low RPM indicates clogging.
  4. Inspect injectors, EGR, and turbo – excess soot from these parts can re-clog the filter.

If the DPF is mechanically clogged with ash, no burn-off will help – professional cleaning or replacement will be necessary.

DPF diagnostics – technician reading OBD codes in a car
DPF diagnostics – reading OBD codes and differential pressure helps assess the degree of clogging.

How to clean a clogged DPF

Cleaning should always be preceded by finding the root cause. Burning off soot or using chemicals without addressing the source will only bring short-term results. In practice, three methods are used to restore filter performance:

1. Active regeneration – burn-off while driving

An automatic process that starts when the filter is slightly clogged. Take a longer drive (20–30 minutes) at steady RPM above 2000 and exhaust temperature above 600°C. The engine burns off accumulated soot. Do not stop until the process completes.

2. Forced regeneration – service burn-off

In a workshop, a technician can initiate regeneration using diagnostic software. It takes several minutes and burns soot, but it does not remove mineral ash.

3. Hydrodynamic or thermal cleaning

The most effective method for heavily clogged filters. The DPF is removed and cleaned with a dedicated machine that flushes out soot and ash. This restores 95–98% efficiency. After such cleaning, check sensors and oil to prevent re-clogging.

How to prevent DPF clogging

To avoid the DPF getting clogged again, follow these simple rules:

  • Once a week drive at least 20–30 minutes outside the city with smooth speed and higher exhaust temperatures.
  • Keep the thermostat, sensors, and EGR in good condition.
  • Use Low-SAPS oil designed for engines with DPF.
  • Refuel with quality diesel and avoid driving at very low RPM.
  • Service the intake system and turbo regularly – they have the greatest impact on filter life.

Following these rules significantly extends filter life and helps avoid expensive repairs.

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Summary

A clogged DPF filter most often affects cars used in the city or with a faulty thermal system. Regular checks, proper use, and preventive cleaning help you avoid costly failures. If you notice the first symptoms, don’t delay diagnostics. The sooner you act, the more likely you’ll save the filter without replacement.

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