Detailed guide for SPN 157 FMI 18
Back to top ↑Don’t guess. Look at commanded vs actual rail pressure. That one graph saves hours of random part swapping.
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Share ↓SPN 157 FMI 18Severity: Critical
SPN 157 FMI 18: Fuel rail pressure below commanded – derate/rough running
Quick Answer
Fuel rail pressure below commanded – derate/rough running
Code
SPN 157 FMI 18
Severity
Critical
Applies to
Check OEM application
Can I drive?
Driving suitability is not established by this code alone.
Common Symptoms
- Rough idle
- Low power under load
- Derate
Likely Causes
- Restriction on supply side
- Pressure control actuator issue
- Leak-off/high-pressure leak
Common Fixes
- Compare commanded vs actual rail pressure
- Fix supply restriction first
- Diagnose control valve/pump only after basics
Full technical sections↓
What does SPN 157 FMI 18 mean?
Back to top ↑Fuel rail pressure below commanded – derate/rough running
Video walkthrough for SPN 157 FMI 18
The videos below are embedded using YouTube’s official player. We do not host or claim ownership of this content. Use it as a visual reference and always confirm with diagnostics for your exact truck configuration.
Truckers Quick Tip Fault Code 559 SPN 157 FMI 18. Low Fuel Pressure in the common rail.
Channel: Engine Shop Joe • View in BigRigFaults Media • YouTube source
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