Diesel Trouble Codes

P0404 — Exhaust Gas Recirculation Control Circuit Range/Performance (LLY / LBZ / LMM Duramax)

Diagnostic reference for LLY/LBZ/LMM Duramax 2004.5–2010. EGR present on all; DPF only on LMM; no SCR/DEF on any. Code indicates EGR control circuit operating…

Updated September 2, 2026

What it means

ECM has detected the EGR control circuit is operating outside its expected range or performance. Generic definition: EGR control circuit range/performance fault. Typical on LLY/LBZ/LMM Duramax 2004.5-2010. EGR present on all; DPF only on LMM. No SCR/DEF on any.1

Most likely causes

  1. EGR valve position feedback / actuator performance fault — EGR valve position sensor or actuator not matching commanded position; carbon sticking, worn pintle, or feedback circuit drift. EGR equipped on LLY/LBZ/LMM.1
  2. EGR control circuit electrical fault — Wiring, connector corrosion, or ECM driver issue for EGR valve control circuit. Generic definition is control circuit range/performance.1
  3. EGR flow modeling mismatch due to intake/air metering — MAF signal outside expected range can affect EGR airflow modeling. MAF feeds EGR/airflow modeling on this platform. MAF range/performance code P0101 definition.2
  4. Excessive or insufficient EGR flow from restriction / leak — Carbon buildup in EGR valve/cooler or intake passages causing flow deviation from command. P0402 is EGR flow excessive; P0401 is EGR flow insufficient on this platform.34

How to diagnose

  1. Verify code and freeze frame; confirm P0404 active and check for companion EGR/airflow codes.
  2. Inspect EGR valve electrical connector and wiring for corrosion, oil contamination, and chafing; check reference/return/ signal voltages per service info.
  3. Command EGR valve position with scan tool and monitor actual vs desired position feedback; look for sticking, slow response, or out-of-range values.
  4. Inspect EGR valve and passages for carbon buildup/restriction; check EGR cooler flow path for blockage. EGR valve+cooler present on LLY/LBZ; LMM adds DPF.
  5. Check intake air metering: inspect MAF sensor and intake duct for contamination/leaks; compare MAF readings to expected at idle and cruise. MAF feeds EGR/airflow modeling.
  6. Review fuel system and injector health if misfire/contribution codes present; external injectors on LLY/LBZ/LMM. Injector circuit malfunction example P0202.
  7. Check turbo VGT operation and boost control circuits; VGT with position feedback on LLY/LBZ/LMM. Turbo boost control solenoid circuit example P0045.
  8. Do not assume catalyst efficiency codes apply; P0420 is not used by GM Duramax ECMs on LLY/LBZ/LMM. LLY/LBZ have DOC only, LMM has DOC+DPF with DPF-specific codes.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by sub-engine and region. LLY 2004.5–2005, LBZ 2006–2007, LMM 2007.5–2010. DPF service applies to LMM only.

When to see a pro

If EGR valve requires removal for cleaning/replacement, or wiring repair near high-temperature exhaust components is needed, have a qualified diesel technician perform the work. Do not service high-pressure fuel lines or safety-critical systems without proper training.

Sources

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

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

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

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