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P2002Diesel & RV
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P2002Diesel particulate filter (DPF) efficiency below threshold (Bank 1)

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Stop the vehicle

— DPF efficiency failure is a stop-level emissions and power issue: derate follows, and a cracked substrate can dump soot. Do not keep forcing regens hoping ash will burn.

What does this severity mean?

General guidance only — not a substitute for a professional inspection or official roadside / out-of-service criteria (e.g. CVSA OOSC) in your jurisdiction.

Part of system: Aftertreatment & emissions systems

Often shows up through monitors and inspection readiness more than a sudden roadside failure. P2002 indicates the diesel particulate filter is no longer trapping soot at the efficiency the ECM expects—often seen as an excessive delta-pressure for a given flow, or soot slipping past a cracked substrate. Unlike a simple high-soot load code, efficiency faults point to a damaged, melted, or ash-overloaded DPF rather than a missed regen. Compare DPF differential pressure to OEM tables at steady cruise, inspect for exhaust leaks between sensors, and review oil consumption that accelerates ash. City-only diesels that rarely complete highway regens are frequent candidates. Typical contributors include cracked, melted, or missing DPF substrate, ash overload from high oil consumption that regen cannot burn, and faulty DPF differential-pressure sensor or clogged tubes. A calm sequence is to graph DPF delta-P versus exhaust flow against OEM charts, then inspect sensor tubes for carbon plugs before condemning the filter, and only afterward budget for dPF assembly or reman unit with gaskets if the data still points there.

Parts that may be involved

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Vehicles often affected

Heavy trucks and diesel pickups on mixed vocational duty—city miles with incomplete regens—are the usual population.

Typical symptoms

  • DPF differential pressure stays high after a successful regen
  • Black soot streaks downstream of the filter can or sensors
  • Repeated regen requests with little drop in soot load PID
  • Exhaust smell and opacity increase under boost
  • Derate after the ECM confirms filter efficiency below threshold

Likely causes

  • Cracked, melted, or missing DPF substrate
  • Ash overload from high oil consumption that regen cannot burn
  • Faulty DPF differential-pressure sensor or clogged tubes
  • Exhaust leak between upstream and downstream pressure ports
  • Chronic incomplete regens leaving uncontrolled soot then thermal damage

Recommended checks

  1. 1

    Graph DPF delta-P versus exhaust flow against OEM charts

  2. 2

    Inspect sensor tubes for carbon plugs before condemning the filter

  3. 3

    Perform OEM ash cleaning or replace the DPF if efficiency fails

  4. 4

    Fix oil consumption and injector faults that overload ash/soot

  5. 5

    Verify no leaks between pressure ports after filter service

DIY vs professional

DIY-safe: inspect sensor tubes and confirm a completed regen did not drop delta-P. Pro: ash cleaning, DPF replacement, and OEM model resets need shop equipment and tooling.

See also

Related discussions

Community threads about this fault code (external forums — opens in a new tab).

Related terms

Content reviewed by a heavy-duty technician. About our editorial approach