What is SPN 970 FMI 31 & How to Solve It?

What is SPN 970 FMI 31:

SPN 970 refers to the Fuel Pressure Control System, and FMI 31 means an abnormal but undefined condition has been detected.

This often points to a fuel system issue that is affecting pressure regulation, even though the ECM cannot pinpoint an exact fault.

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Why This Happens

• Low fuel pressure or restriction in the supply line.
• Fuel pressure relief valve stuck or malfunctioning.
• Contaminated fuel or blocked filters.
• Fuel rail pressure sensor giving unstable readings.
• Faulty high-pressure pump or control solenoid.

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How to Fix It

1. Check fuel levels and ensure the system is primed properly.
2. Replace fuel filters if clogged or overdue.
3. Test fuel rail pressure sensor with a scan tool.
4. Inspect the high-pressure pump and lines for leaks or blockage.
5. Clear the code and monitor system pressure during engine load.

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How to Avoid It Before It Happens

1. Use clean, water-free fuel stored in sealed tanks.
2. Replace filters on time to avoid injector and pump damage.
3. Monitor fuel pressure trends to detect early warning signs.
4. Keep track of injector wear and rail pressure behavior.

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