Cummins Fault Code
Free · no signupSPN 3521 FMI 0
Low Power.
System
Not specified
Symptom
Low Power.
Diagnosis & fix steps
LOGIC: SCR Catalyst Conversion Efficiency Low.
ACTION: Verify DEF quality with a refractometer; check NOx sensors for drift using Insite.
Red Seal field insights
This is the most searched code for Cummins Stage V. Red Seal Fix: Before replacing the catalyst, check for "face plugging" (crystal buildup) at the SCR inlet pipe.
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