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 4374 FMI 16: Meaning and Fix SPN 4374 FMI 16 indicates the DEF pump motor speed has exceeded the normal operating threshold without reaching critical failure levels, classified as moderately severe per SAE J1939. The SCR aftertreatment controller monitors pump rpm continuously; when commanded dosing flow doesn’t match actual motor feedback, this … Read more
Diagnostic Code SPN 3719 FMI 8: Meaning and Fix SPN 3719 FMI 8 indicates the ECM is receiving an abnormal frequency, pulse width, or period in the soot load percent signal from the Aftertreatment 1 DPF system. This fault commonly appears after a forced DPF regeneration cycle where differential pressure sensor signals become erratic due … Read more
Diagnostic Code SPN 3719 FMI 21: Meaning and Fix SPN 3719 FMI 21 monitors the soot load percentage of Diesel Particulate Filter (DPF) 1. A low data drift suggests potential sensor inaccuracies. This fault often appears after a failed regeneration cycle, where the expected drop in soot load percentage does not align with sensor readings. … Read more
Diagnostic Code SPN 3719 FMI 20: Meaning and Fix This fault indicates the aftertreatment 1 diesel particulate filter soot load percent sensor signal has drifted above the expected range. The ECM detects a value consistently higher than the physically plausible model. Technicians frequently encounter this code after a forced DPF regeneration that was interrupted or … Read more
Diagnostic Code SPN 3719 FMI 19: Meaning and Fix SPN 3719 FMI 19 activates when the ECM receives erroneous or invalid data for Aftertreatment 1 DPF Soot Load Percent via the SAE J1939 CAN network. FMI 19 specifically flags a network data integrity failure, not a sensor hardware fault. This fault commonly appears after an … Read more
Diagnostic Code SPN 3719 FMI 17: Meaning and Fix The SPN 3719 FMI 17 code indicates that the soot load percent in Diesel Particulate Filter 1 is below the normal operating range. This fault commonly appears after a regeneration cycle fails to complete properly, often due to unfavorable conditions like low engine load or short … Read more
Diagnostic Code SPN 3719 FMI 10: Meaning and Fix This fault indicates the soot load percent signal from the DPF is changing at an abnormal rate, exceeding the ECM’s plausibility limits. Technicians often see this after a forced DPF regeneration that was interrupted or after replacing the DPF without resetting soot load values. The ECM … Read more
Diagnostic Code SPN 3361 FMI 8: Meaning and Fix SPN 3361 FMI 8 indicates the ECM has detected an abnormal frequency, pulse width, or period from the Aftertreatment 1 DEF Dosing Unit 1. The dosing unit’s PWM control signal falls outside calibrated timing windows, disrupting precise urea injection into the exhaust stream. This fault commonly … Read more
Diagnostic Code SPN 3361 FMI 21: Meaning and Fix The aftertreatment 1 diesel exhaust fluid dosing unit 1 reports a signal voltage or current reading that has drifted below the calibrated minimum threshold. This occurs when the internal pressure sensor or actuator feedback circuit outputs a value lower than the ECM expects. Technicians often see … Read more
Diagnostic Code SPN 3361 FMI 20: Meaning and Fix SPN 3361 FMI 20 indicates the Aftertreatment 1 DEF Dosing Unit 1 feedback signal has drifted above its calibrated operating threshold, triggering a data-drifted-high fault. The ECM detects dosing unit output exceeding expected parameters during closed-loop SCR control. This fault commonly appears in cold-climate conditions where … Read more