Diesel Trouble Codes

P0402 — Exhaust Gas Recirculation Flow Excessive (6.7 Cummins (SCR / DEF))

Diagnostic reference for 6.7L Cummins SCR/DEF 2013–present.

Updated September 2, 2026

What it means

Measured EGR flow is higher than commanded. Generic definition: measured EGR flow higher than commanded. Typical on this platform: 6.7L Cummins 2013–present SCR/DEF — authoritative hardware facts provided.1

Most likely causes

  1. EGR valve stuck open / failing position control — Valve fails to close, or electric actuator/position feedback drifts, causing excess recirculated exhaust. On 6.7 Cummins SCR/DEF the EGR valve + cooler are present.1
  2. EGR cooler internal restriction / carbon plugging causing flow imbalance — Cooler blockage can alter pressure differential and cause the PCM to see higher-than-commanded flow. EGR hardware present on this platform.1
  3. Intake/EGR passage carbon buildup increasing effective flow — Heavy soot in intake manifold and EGR passages can change flow characteristics, leading to excessive measured flow. EGR hardware present.1
  4. Faulty EGR position / feedback sensor or wiring — Erroneous position feedback makes PCM think valve is more closed/open than actual, resulting in over-flow detection. EGR system affected.1
  5. PCM calibration / learned adaptation drift — Adaptations can drift with age and soot loading, causing commanded vs measured mismatch. Generic definition applies.1

How to diagnose

  1. Verify code and freeze frame; confirm P0402 sets under steady cruise/light load where EGR is commanded.
  2. Inspect EGR valve operation and position feedback using scan tool data; compare commanded vs actual position.
  3. Check intake and EGR passages for excessive carbon restriction/buildup.
  4. Inspect EGR cooler for internal blockage or external leaks.
  5. Check EGR-related wiring/connectors for corrosion or chafing; verify reference/return voltages.
  6. Review recent repairs, calibrations, and soot loading history; check for accompanying EGR or intake restriction codes.

Parts and tools you may need

Rough cost and difficulty

Cost varies by model year and labor; EGR valve/cooler replacement and intake cleaning are common repairs on this platform.

When to see a pro

If diagnosis points to internal EGR cooler failure, high-pressure fuel system, or requires PCM reprogramming, 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 — 6.7 Cummins (SCR / DEF) (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

Watch a repair

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

2016 Ford 6.7L (P0402) — BL Automotive · 47K views

2019 6.7 Powerstroke EGR Maintenance: The Problem With Carbon Build-Up — Dave's Auto Center · 170K views

Ford EGR Flow Testing (P0401, P0402, P0405) — ScannerDanner · 699K views