P2002 – DPF Efficiency Below Threshold

The ECU believes the diesel particulate filter is not reducing soot/particles as expected.

Plain‑English Explanation

P2002 is often triggered when calculated soot loading and pressure/temperature behaviour don’t match what the ECU expects during normal driving and regeneration cycles. It can be caused by a genuinely restricted DPF, faulty sensors or a long-term issue that’s producing excess soot.

Common Symptoms

  • Warning light related to DPF/emissions (varies by car).
  • Reduced power or limited torque, especially on sustained load.
  • Cooling fans running after shutdown and higher fuel consumption.
  • Frequent or failed regenerations.

Common Causes

  • DPF soot load too high due to short trips or repeated interrupted regenerations.
  • DPF pressure sensor faults or blocked/damaged pressure lines.
  • Exhaust temperature sensor faults causing incorrect regeneration control.
  • Underlying EGR/boost/injector issues increasing soot output.
  • DPF physically damaged, melted, cracked, modified or removed.

Good Diagnostic Order

  1. Read out DPF soot load, ash load and regeneration history using a capable scan tool.
  2. Check DPF pressure sensor readings for plausibility at idle and with a brief throttle blip.
  3. Inspect pressure sensor pipes/hoses for blockage, splits or heat damage.
  4. Look for related codes (EGR, boost, injector, temperature sensors) and fix those first.
  5. Only consider a forced regeneration once root causes and sensor data are stable.

When Not to Panic

  • If the car has done lots of short trips, a successful regen and corrected driving pattern may clear it.
  • If a pressure sensor pipe is blocked, fixing the pipe/sensor can resolve P2002 without replacing the DPF.