What is SPN 1347 FMI 4 & How to Solve It?

What is SPN 1347 FMI 4:

This code indicates that the DPF intake pressure sensor is reading below normal — likely caused by a signal short to ground.

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Why This Happens

• Sensor signal wire is shorted to ground.
• Faulty sensor internal circuit.
• Broken or pinched wiring in the exhaust harness.

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How to Fix It

1. Inspect and repair the sensor harness.
2. Test sensor output voltage using diagnostics.
3. Replace the pressure sensor if voltage is too low.
4. Clear the fault and verify pressure readings during regen.

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How to Avoid It Before It Happens

1. Use insulated harnesses around high-temp exhaust areas.
2. Replace sensors during scheduled DPF maintenance.