What is SPN 3242 FMI 18 & How to Solve It?

What is SPN 3242 FMI 18:

SPN 3242 FMI 18 indicates a fault with the Selective Catalytic Reduction (SCR) System Diesel Exhaust Fluid (DEF) Pressure Sensor Circuit – Data Valid But Above Normal Operational Range. This means the sensor is sending data that is higher than the expected operating range, which can affect the DEF injection and emission control system performance.

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Why This Happens

Common causes include:

• Faulty DEF pressure sensor.
  
• Blockages or restrictions in the DEF injection lines.
  
• Wiring issues such as damaged or corroded connectors.
  
• Faulty Engine Control Module (ECM) or sensor calibration errors.
  
  

How to Fix It

To resolve this fault:

1. Inspect the DEF pressure sensor and wiring for damage or corrosion.
   
2. Check DEF injection lines for blockages or restrictions.
   
3. Test the sensor signal and replace if faulty.
   
4. Repair or replace damaged wiring or connectors.
   
5. Clear the fault code and verify system operation.
   
   

How to Avoid It Before It Happens

Prevent this fault by:

• Regularly inspecting the DEF system sensors and wiring.
  
• Maintaining clean and clear DEF injection lines.
  
• Performing routine diagnostics to catch sensor issues early.
• Use Clue’s Preventive Maintenance to schedule regular checks on the DEF system and sensors to prevent performance issues and catch potential faults early.