What is SPN 3490 FMI 7 & How to Solve It?

What is SPN 3490 FMI 7:

SPN 3490 FMI 7 indicates a fault with the Aftertreatment 1 Diesel Exhaust Fluid (DEF) Injection Valve Control Circuit – Voltage Below Normal or Shorted to Low. This means the engine control module (ECM) has detected that the voltage in the DEF injection valve control circuit is lower than expected, which can prevent proper DEF injection and reduce emissions control efficiency.

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Why This Happens

Common causes include:

• Faulty DEF injection valve or control module.
  
• Damaged, shorted, or corroded wiring or connectors in the valve circuit.
  
• Faulty ECM not properly controlling the valve.
  
• Clogged or contaminated DEF injector.
  
  

How to Fix It

To resolve this fault:

1. Inspect the DEF injection valve and wiring for damage or corrosion.
   
2. Test the DEF injection valve control circuit voltage and replace components if faulty.
   
3. Repair or replace damaged wiring or connectors.
   
4. Clean or replace the DEF injector if clogged.
   
5. Clear the fault code and verify injector operation.
   
   

How to Avoid It Before It Happens

Prevent this fault by:

• Regularly inspecting the DEF injection valve and wiring.
  
• Using high-quality DEF fluid to prevent clogging.
  
• Performing routine maintenance and diagnostics to catch issues early.
• Use Clue’s Preventive Maintenance to regularly inspect the DEF injection valve, wiring, and connections, ensuring they remain in good condition and prevent performance issues.