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SPN 157 FMI 1

Injector Metering Rail 1 Pressure (Fuel Rail) — Value too low (most severe).
The reading is valid but far below the normal operating range, at the most serious 'too low' level.

What the SPN covers: High-pressure fuel rail pressure on common-rail engines. More on SPN 157.

What FMI 1 usually points to: A real under-condition such as very low oil pressure or low fuel pressure, or a sensor that has drifted low. More on FMI 1.

Severity

HIGH — limit use, diagnose now

Rail pressure problems can cause stalling, no-start or severe derates. Avoid heavy work until fixed.

Likely causes

  1. Low fuel supply pressure (filters, lift pump, air)
  2. Worn high-pressure pump
  3. Leaking injector return or pressure relief valve
  4. Failed rail pressure sensor or wiring
  5. Fuel pressure regulator / inlet metering valve fault

Checks & fixes (easiest first)

  1. Start with fuel supply: filters, priming, air in fuel
  2. Compare desired vs. actual rail pressure on a scan tool
  3. Perform injector return flow test per OEM
  4. Inspect the rail pressure sensor connector

FAQ

What does SPN 157 FMI 1 mean?

Injector Metering Rail 1 Pressure (Fuel Rail) — value too low (most severe). The reading is valid but far below the normal operating range, at the most serious 'too low' level.

Is SPN 157 FMI 1 serious?

Rail pressure problems can cause stalling, no-start or severe derates. Avoid heavy work until fixed.

What should I check first for SPN 157 FMI 1?

Start with fuel supply: filters, priming, air in fuel; Compare desired vs. actual rail pressure on a scan tool; Perform injector return flow test per OEM.