What is SPN 4377 & How to Solve It?

What is SPN 4377:

This code refers to a problem with the DEF dosing valve circuit — generally involving failed activation or a dead response from the component.

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Why This Happens

• DEF dosing valve failed electrically.
• Connector corroded or unplugged.
• Open circuit in control wiring.
  
  

How to Fix It

1. Inspect wiring and connector going to the dosing valve.
2. Use diagnostics to command valve on/off and verify response.
3. Replace the valve if no signal or motion is detected.
4. Clear the fault and confirm DEF injection during operation.
   
   

How to Avoid It Before It Happens

1. Replace DEF dosing valves proactively based on duty cycle.
2. Keep connectors sealed and protected.