Cummins Fault Code
Free · no signupSPN 3216 FMI 20
DEF usage is high or low; Frequent parked regens; "Derate" timer may start; Check engine light.
Variant 1
System
Not specified
Symptom
DEF usage is high or low; Frequent parked regens; "Derate" timer may start; Check engine light.
Diagnosis & fix steps
DEF usage is high or low; Frequent parked regens; "Derate" timer may start; Check engine light.
LOGIC: NOx sensor reading is "drifting" out of range compared to the outlet sensor.
ACTION: Check for exhaust leaks upstream of the sensor. Inspect sensor tip for soot/moisture contamination.
FIX: Repair exhaust leaks or replace the Inlet NOx Sensor (and its control module).
Red Seal field insights
NOx sensors are extremely sensitive to moisture. Never "wash" an exhaust system with a pressure washer while the sensors are hot, or you'll crack the ceramic element inside.
Variant 2
System
Aftertreatment
Symptom
Aftertreatment Derate
Diagnosis & fix steps
LOGIC: Inlet NOx Sensor Drifted High.
ACTION: Perform an "Analyzer" test on the NOx sensor. Replace if reading >50ppm at idle.
Red Seal field insights
Logic: The sensor is "talking" but giving inaccurate data.
FIX: This often triggers a "False" DPF soot load warning.
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