What is SPN 729 FMI 5 & How to Solve It?

What is SPN 729 FMI 5:

SPN 729 FMI 5 refers to a low voltage condition in the Intake Manifold Air Temperature (IMAT) sensor circuit. This sensor measures the temperature of air entering the engine, allowing the ECM to adjust fuel delivery for optimal combustion. FMI 5 specifically means that the signal voltage is below the expected range, often due to electrical or sensor issues.

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Why This Happens

• Faulty or failing IMAT sensor.
  
• Short to ground or damaged wiring.
  
• Corroded or loose electrical connectors.
  
• Poor ECM connection or ground.
  
• Incorrect sensor installation or contamination.
  
  

How to Fix It

1. Inspect the IMAT sensor and connector for signs of corrosion or damage.
   
2. Check wiring harness for shorts or exposed wires.
   
3. Test voltage and ground supply at the sensor connector.
   
4. Measure resistance of the sensor and compare to OEM specifications.
   
5. Replace the IMAT sensor if it’s out of spec and clear the code.
   
   

How to Avoid It Before It Happens

• Perform regular inspections of intake and sensor wiring.
  
• Keep sensor connectors sealed and clean.
  
• Avoid pressure washing or exposing intake sensors to moisture.
  
• Replace sensors at intervals recommended by the manufacturer.
  
• Address early symptoms like hard starts or erratic idle promptly.
• Use Clue’s Preventive Maintenance to regularly inspect sensor wiring and connectors, ensuring they are sealed and free from damage to avoid voltage issues.