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SPN 157Heavy truck
Hard

SPN 157 — Injector metering rail pressure — data erratic, intermittent, or incorrect

The common-rail injection pressure sensor or circuit is sending unstable signals. That can cause surging, power loss, and roadside shutdowns—especially under heavy load.

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Likely causes

  • Intermittent rail pressure sensor or loose connector
  • Worn high-pressure injection pump or air in the fuel system
  • Internal leak at the pressure regulator or a bad injector

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Recommended checks

  1. 1

    Use a scope or scan tool to capture pressure swings while driving

  2. 2

    Bleed the fuel system and replace the filter

  3. 3

    Replace the rail sensor or HP pump if confirmed bad

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Parts to replace