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P0402Diesel & RV
Moderate

P0402 — EGR flow excessive detected

The EGR system is flowing too much exhaust into the intake. That can cause rough idle, surging, and power loss—especially on diesel trucks.

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Likely causes

  • EGR valve stuck open or bad position sensor
  • Carbon deposits preventing full valve closure
  • Incorrect EGR command from a bad MAP/MAF sensor

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Recommended checks

  1. 1

    Clean or replace the EGR valve

  2. 2

    Compare commanded vs actual EGR position on the scan tool

  3. 3

    Test MAP/MAF sensors that drive EGR logic

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Parts to replace