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P242F Generic (SAE)

Diesel Particulate Filter Restriction - Ash Accumulation

Updated 2026-10-02 · Fuel, air & emissions (P2)

Severity
High
Typical repair cost
250 – 3 000 EUR
System
Powertrain

What it means

A DPF collects two things: soot, which regeneration burns off at 550-650 °C, and ash from engine oil additives and fuel, which cannot burn and stays in the filter forever. P242F sets when the ECM's ash model, built from mileage, oil consumption and the differential pressure measured right after a completed regeneration, exceeds the design limit (often 50-120 g depending on filter size). Unlike soot codes, this cannot be fixed by driving or forced regeneration.

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Symptoms

  • DPF and engine warning lamps on, power reduced
  • Regenerations occur very frequently (every 100-200 km) and last longer
  • Rising fuel consumption and oil level (fuel dilution from post-injection)
  • Lack of boost feel, sluggish at high RPM due to back pressure
  • High mileage vehicle (typically 150,000-250,000 km) with no other faults

Common causes

  1. Normal end of life: ash from oil additives accumulated over 150,000-250,000 km
  2. Use of non-low-ash (non-Low SAPS) engine oil accelerating ash build-up
  3. High oil consumption from worn turbo seals, valve guides or piston rings
  4. Frequent regenerations from short-trip use burning more oil-derived ash
  5. Faulty differential pressure sensor or blocked/cracked pressure hoses giving false high ash estimate
  6. Ash model counter not reset after a previous DPF replacement or cleaning

How to diagnose

  1. Read the DPF data block: soot load (g), ash load (g), kilometres since last regeneration and number of regenerations. Ash above the manufacturer limit (e.g. more than 60-80 g on a typical 2.0 L passenger car filter) with normal soot confirms the code is genuine.
  2. Check the differential pressure at idle after a completed regeneration: typically 5-15 mbar with a clean filter; 30-50 mbar or more at idle with low soot load means the filter is physically full of ash.
  3. Verify the sensor: with the engine off both ports see atmosphere and the sensor must read 0 mbar (output around 0.5-1.0 V); disconnect the hoses and blow gently to confirm response, inspect hoses for cracks, kinks and soot blockage.
  4. Rev the engine to 3000 rpm: differential pressure above 150-200 mbar with the engine warm indicates heavy restriction regardless of the model value.
  5. Check oil specification (ACEA C1-C4 Low SAPS required) and oil consumption history; if consumption exceeds about 0.5 L per 1000 km, repair the oil source first or the new filter will fill quickly.
  6. Remove the DPF for professional cleaning (thermal and liquid, typically 250-500 EUR) or replace it, then reset the ash counter and adaptations with the scan tool and perform a verification regeneration.

Frequently asked questions

Will a forced regeneration clear P242F?

No. Regeneration burns soot, not ash. Ash is mineral residue and can only be removed by cleaning the filter off the car or replacing it. Forcing repeated regenerations only wastes fuel and risks cracking the substrate.

Is cleaning as good as a new filter?

Professional cleaning typically restores 90-98 % of capacity and costs a fraction of a new OEM filter (which can be 1500-3000 EUR). The substrate must be inspected for cracks and melted channels first.

Symptoms linked to this code

Terms to know

Diesel particulate filter (DPF)Adaptation reset and basic settings

Related codes

P2002P2452P2453P2454P2458P2459P244AP244B

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