Diesel Trouble Codes

P2002 — Diesel Particulate Filter Efficiency Below Threshold (Bank 1) (LLY / LBZ / LMM Duramax)

Diagnostic reference for LLY/LBZ/LMM Duramax 2004.5–2010. DPF codes apply to LMM only; LLY/LBZ have no DPF hardware.

Updated September 2, 2026

What it means

P2002 means the ECM judges DPF filtering efficiency below threshold using pressure/temperature data. On this platform DPF codes apply to LMM only; LLY/LBZ have no DPF hardware.1

Most likely causes

  1. DPF physically removed or disabled (aftermarket delete). — Aftermarket removal disables the monitored aftertreatment; efficiency monitor cannot be satisfied. NHTSA reports of DPF physically removed on used Duramax trucks.2
  2. Excessive soot loading / clogged DPF from incomplete or interrupted regenerations. — High soot mass raises differential pressure and lowers efficiency; regeneration frequency codes are DPF-specific on this platform.3
  3. DPF differential pressure sensor / tubing fault giving false efficiency low. — Erroneous pressure readings cause the ECM to calculate low efficiency. DPF monitoring uses pressure/temperature data.1
  4. Faulty DPF temperature sensors leading to incorrect regeneration control. — Temperature input errors affect soot burn calculations; efficiency judged by pressure/temperature data.1
  5. Excessive oil ash accumulation from engine oil consumption or wrong oil. — Ash permanently fills DPF volume, reducing filtration efficiency over time. DPF is present only on LMM.1

How to diagnose

  1. Verify sub-engine: confirm LMM 2007.5–2010; LLY/LBZ have no DPF and P2002 does not apply.
  2. Scan for companion DPF codes (e.g., P2459 regeneration frequency) and check freeze frame for mileage/load.
  3. Inspect aftertreatment visually for tampering/delete; look for missing DPF, straight pipe, or altered sensors.
  4. Check DPF differential pressure sensor readings at idle and under load; inspect pressure tubes for soot blockage or leaks.
  5. Check DPF temperature sensor values vs. expected during regen; compare bank 1 sensors.
  6. Review recent drive cycles for completed regenerations; frequent regens suggest excessive soot/oil ash.

Parts and tools you may need

Rough cost and difficulty

Cost varies by root cause; DPF replacement is high; sensor/tubing faults are lower cost. Delete-related faults require restoration to OEM configuration for monitor readiness.

When to see a pro

If DPF is removed or modified, professional restoration to OEM emissions configuration is required for legal operation and monitor readiness. If differential pressure remains high after confirming sensors, professional evaluation of DPF condition and regeneration history is needed.

Sources

  1. Curated DTC seed — LLY / LBZ / LMM Duramax (curated) ↩︎ ↩︎ ↩︎ ↩︎

  2. NHTSA owner report 10816648 ↩︎

  3. Curated DTC seed — LLY / LBZ / LMM Duramax (curated) ↩︎

Watch a repair

Third-party videos, not ours — for illustration. Confirm anything against the factory service information for your truck.

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