What is SPN 1239 FMI 17 & How to Solve It?

What is SPN 1239 FMI 17:

SPN 1239 refers to the Aftertreatment Fuel Injector, and FMI 17 indicates the sensor or injector is reporting a value below expected range — often tied to low performance or weak fuel delivery during regeneration.

This code means the aftertreatment injector is not supplying enough fuel, which can result in incomplete regenerations or high soot accumulation in the DPF.

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Why This Happens

• Injector partially clogged or carbon fouled.
• Weak fuel pressure at injector inlet.
• Faulty wiring or solenoid issue in the injector.
• Blocked fuel line or failing delivery valve.
• Software error misinterpreting injector response.

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How to Fix It

1. Check injector wiring and connector for damage.
2. Test fuel pressure during regen cycles.
3. Clean or replace the aftertreatment injector if flow is restricted.
4. Inspect fuel supply lines for blockage.
5. Run a forced regen and monitor injector behavior.
6. Clear the code and verify that regeneration completes successfully.

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How to Avoid It Before It Happens

1. Use high-quality diesel fuel and change filters on time.
2. Include aftertreatment injector checks in your PM schedule.
3. Run diagnostic test regens during servicing.
4. Replace injectors showing weak or late spray patterns.