SPN 4364 / FMI 18
SCR Conversion Efficiency — Low (Moderate)
SAE J1939
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SPN 4364
FMI 18
What it means
Aftertreatment 1 SCR NOx conversion below threshold — DEF quality, dosing, or aged catalyst.
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Run a free diagnosisRelated codes
SPN 1761 / FMI 1
DEF Tank Level — Below Normal (Most Severe)
scrHigh
SPN 1761 / FMI 3
DEF Tank Level Sensor — Voltage High
scrLow
SPN 3216 / FMI 2
Aftertreatment Intake NOx — Data Erratic
scrMedium
SPN 3226 / FMI 2
Aftertreatment Outlet NOx — Data Erratic
scrMedium
SPN 3361 / FMI 5
DEF Dosing Unit — Current Below Normal/Open
scrHigh
SPN 3364 / FMI 1
DEF Quality — Below Normal
scrHigh
SPN 4094 / FMI 0
SCR Operator Inducement — Severe
scrCritical
SPN 4334 / FMI 1
DEF Dosing Pressure — Below Normal
scrHigh
General reference only — always confirm against the OEM procedure for your specific engine.