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 3361 FMI 19: Meaning and Fix SPN 3361 FMI 19 refers to an error in network data related to the Aftertreatment 1 Diesel Exhaust Fluid Dosing Unit 1. This fault often arises following an incorrect DEF refill or after ECM software updates. In practice, this can lead to poor emissions control and … Read more
Diagnostic Code SPN 3361 FMI 17: Meaning and Fix The DEF dosing unit 1 (bank 1) signal is valid but below the normal operating range, indicating insufficient delivery pressure or electrical feedback. This fault commonly appears after a forced DPF regeneration when the dosing unit was not properly primed, leading to air ingestion and reduced … Read more
Diagnostic Code SPN 3361 FMI 16: Meaning and Fix SPN 3361 FMI 16 indicates the Aftertreatment 1 DEF Dosing Unit 1 is operating above its normal pressure or flow range, classified as moderately severe by SAE J1939. The ECM detects a valid but elevated signal exceeding calibrated thresholds for the dosing unit. This fault commonly … Read more
Diagnostic Code SPN 3361 FMI 15: Meaning and Fix SPN 3361 FMI 15 indicates an issue with the Aftertreatment 1 Diesel Exhaust Fluid Dosing Unit 1, where the data is valid but above the normal operating range. This fault often appears after a DEF dosing unit replacement or following system calibration. The dosing unit’s role … Read more
Diagnostic Code SPN 3361 FMI 10: Meaning and Fix This fault indicates the ECM detected an abnormal rate of change in the DEF dosing unit 1 position or pressure feedback signal. The rate of change exceeded the calibrated threshold within a defined time window. Technicians often encounter this after a forced DPF regeneration when the … Read more
Diagnostic Code SPN 4374 FMI 8: Meaning and Fix SPN 4374 FMI 8 is triggered when the ECM detects an abnormal frequency, pulse width, or period from the DEF pump 1 motor speed sensor signal in aftertreatment system 1. This fault commonly appears during cold-weather startups when DEF fluid thaws unevenly, causing erratic pump motor … Read more
Diagnostic Code SPN 4374 FMI 21: Meaning and Fix SPN 4374 FMI 21 indicates the DEF pump motor speed signal has drifted below the expected operating range, typically below 200 rpm during commanded operation. This fault commonly appears after a failed DEF system priming event or following a low fluid level warning. Technicians often encounter … Read more
Diagnostic Code SPN 4374 FMI 20: Meaning and Fix SPN 4374 FMI 20 indicates the DEF pump motor speed signal has drifted abnormally high beyond calibrated thresholds within Aftertreatment System 1. The ECM receives rotational feedback exceeding expected operational RPM limits, triggering a data-drifted-high fault. This fault commonly appears after DEF pump assembly replacement when … Read more
Diagnostic Code SPN 4374 FMI 19: Meaning and Fix SPN 4374 FMI 19 indicates a problem with the rotational speed data of the diesel exhaust fluid pump motor. This fault often surfaces when erroneous network data is received, causing operational inefficiencies in the aftertreatment system. A common scenario for this fault is post-ECM replacement, where … Read more
Diagnostic Code SPN 4374 FMI 17: Meaning and Fix SPN 4374 FMI 17 indicates the DEF pump motor speed is below the expected minimum threshold while the data signal remains valid. This fault often appears after a failed priming cycle, such as when the pump runs dry due to an empty tank or a blocked … Read more