SAE J1939 SPN and FMI codes for exhaust aftertreatment systems. Covers Diesel Particulate Filter (DPF), Selective Catalytic Reduction (SCR), Diesel Oxidation Catalyst (DOC), Diesel Exhaust Fluid (DEF), EGR, and NOx sensors on emissions-controlled engines.
Diagnostic Code SPN 3364 FMI 18: Meaning and Fix This fault indicates the DEF quality sensor detects fluid characteristics below acceptable operating parameters. Commonly occurs after refilling with contaminated or diluted DEF, particularly in fleets using bulk storage systems where water contamination from condensation affects urea concentration. The ECM continuously monitors conductivity and temperature to … Read more
Diagnostic Code SPN 3363 FMI 7: Meaning and Fix SPN 3363 FMI 7 indicates the Aftertreatment 1 DEF Tank Heater is not responding properly to the commanded heating percentage, typically between 0-100%. This code often appears after a failed forced DPF regeneration in cold climates, where the heater cannot maintain the required DEF temperature, leading … Read more
Diagnostic Code SPN 3363 FMI 5: Meaning and Fix SPN 3363 FMI 5 refers to an open circuit or low current condition in the DEF tank heater. The heater is crucial for preventing DEF crystallization in cold conditions. This issue commonly arises in winter when the heater fails to activate due to an open circuit. … Read more
Diagnostic Code SPN 3362 FMI 14: Meaning and Fix This fault indicates special maintenance instructions are required for the diesel exhaust fluid dosing unit input lines serving the mixing chamber for DEF and compressed air. Technicians commonly encounter this code during scheduled aftertreatment system service intervals or following DEF system component replacement procedures. The FMI … Read more
Diagnostic Code SPN 3361 FMI 3: Meaning and Fix SPN 3361 FMI 3 indicates excessive voltage supply to the DEF dosing unit control circuit, typically exceeding 5.5V threshold. This fault commonly appears after ECM replacement when harness integrity wasn’t verified, or during winter operations when dosing unit heater circuits develop shorts. The dosing unit’s PWM … Read more
Diagnostic Code SPN 3360 FMI 9: Meaning and Fix SPN 3360 with FMI 9 is a diagnostic trouble code indicating an abnormal update rate in the diesel exhaust fluid controller. Often emerging after ECM replacements, this fault affects the controller’s ability to accurately monitor the selective catalytic reduction (SCR) system. Common scenarios include post-maintenance test … Read more
Diagnostic Code SPN 3251 FMI 4: Meaning and Fix SPN 3251 FMI 4 indicates the ECM detected voltage below normal or a short-to-low condition on the aftertreatment 1 DPF differential pressure sensor circuit. This fault commonly appears after a forced DPF regeneration or sensor replacement when connectors are not fully seated. Technicians frequently encounter this … Read more
Diagnostic Code SPN 3251 FMI 3: Meaning and Fix SPN 3251 FMI 3 refers to voltage above normal or shorted high in the aftertreatment 1 diesel particulate filter differential pressure sensor. This fault often appears after a forced DPF regeneration, indicating an anomaly in pressure readings. The ECM might misinterpret a sensor fault as excessive … Read more
Diagnostic Code SPN 3251 FMI 10: Meaning and Fix SPN 3251 FMI 10 indicates an abnormal rate of change in DPF differential pressure across the particulate filter on exhaust bank 1. This fault commonly appears during active regeneration cycles when pressure changes occur too rapidly for normal ECM calibration parameters. Technicians frequently encounter this code … Read more
Diagnostic Code SPN 3226 FMI 3: Meaning and Fix SPN 3226 FMI 3 indicates a high voltage in the Aftertreatment 1 Outlet NOx 1 sensor, often due to a short circuit. This issue frequently arises after a forced DPF regeneration, causing the ECM to detect erroneous NOx levels. Technicians may observe irregularities in emissions control, … Read more