P0402 — Exhaust Gas Recirculation Flow Excessive — 6.7 Cummins (SCR / DEF)
Diagnostic reference for 6.7L Cummins SCR/DEF 2013–present.
What it means
Measured EGR flow is higher than commanded. Generic definition: measured EGR flow higher than commanded.1
Most likely causes
- 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
- 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
- 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
- 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
- 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
- Verify code and freeze frame; confirm P0402 sets under steady cruise/light load where EGR is commanded.
- Inspect EGR valve operation and position feedback using scan tool data; compare commanded vs actual position.
- Check intake and EGR passages for excessive carbon restriction/buildup.
- Inspect EGR cooler for internal blockage or external leaks.
- Check EGR-related wiring/connectors for corrosion or chafing; verify reference/return voltages.
- Review recent repairs, calibrations, and soot loading history; check for accompanying EGR or intake restriction codes.
Common mistake to avoid
Replacing the EGR valve without testing it. If the valve still moves freely, a carbon cleaning often fixes the flow code; and if it opens on command but the code stays, the blockage is in the passages or cooler, not the valve. Source: FleetRabbit — EGR valve problems and repair.
Parts and tools you may need
- Scan tool with live EGR commanded/actual data
- Digital multimeter
- Borescope
- Basic hand tools for inspection covers
Tools you’ll need
- OBD-II scan tool — Reads P0402 freeze frame and live EGR commanded vs actual position data to confirm excess flow under cruise.
- digital multimeter — Checks EGR position sensor reference, signal, and return voltages and wiring integrity for feedback errors.
- borescope — Inspects intake/EGR passages and cooler internals for carbon buildup or blockage without disassembly.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| EGR valve/passage carbon cleaning | $20–$100 | 1–4 hrs | DIY with tools and a manual |
| EGR position/temperature/differential pressure sensor | $60–$300 | 0.5–1.5 hrs | DIY with tools and a manual |
| EGR valve | $400–$1,000 | 1–3 hrs | DIY with tools and a manual |
| EGR cooler | $400–$1,200 | 4–8 hrs | Shop |
Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.
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.
Check for recalls
Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.
Sources
Repair videos: P0402 on the 6.7 Cummins '13+
Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.
Spotted an error, or something missing? Tell us
Run a 6.7 Cummins (SCR / DEF)? This goes straight to the editor — it is not published.