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 3216 FMI 10: Meaning and Fix SPN 3216 with FMI 10 indicates an abnormal rate of change in NOx levels detected in exhaust bank 1. This fault often emerges after a sensor replacement or a SCR system service. Technicians might encounter this code during routine emissions testing or when vehicles undergo extended … Read more
Diagnostic Code SPN 1761 FMI 9: Meaning and Fix SPN 1761 FMI 9 indicates the aftertreatment DEF tank level sensor is providing data at an abnormal update rate to the ECM. This fault commonly appears after ECM reflashing or when technicians encounter intermittent DEF level readings during routine maintenance. The sensor should transmit volume percentage … Read more
Diagnostic Code SPN 5394 FMI 5: Meaning and Fix The SPN 5394 FMI 5 code pertains to the diesel exhaust fluid doser valve, signaling a current below normal or an open circuit condition. This fault often occurs after a forced diesel particulate filter (DPF) regeneration, where increased system pressure can stress electrical connections. In practice, … Read more
Diagnostic Code SPN 4374 FMI 0: Meaning and Fix Excessive motor speed in the DEF pump system often occurs post-ECM replacement, affecting the exhaust aftertreatment process. SPN 4374 FMI 0 indicates that the motor speed is above the normal operational range, leading to potential over-injection of diesel exhaust fluid. This fault typically surfaces after forced … Read more
Diagnostic Code SPN 4364 FMI 1: Meaning and Fix SPN 4364 FMI 1 indicates the SCR catalyst conversion efficiency has dropped below the normal operational threshold, calculated as (inlet NOx – outlet NOx) / inlet NOx × 100. This fault commonly appears after a forced DPF regeneration when hot spots degrade the catalyst or when … Read more
Diagnostic Code SPN 3364 FMI 2: Meaning and Fix The aftertreatment 1 DEF tank quality sensor reports data that is erratic, intermittent, or incorrect. This typically occurs after a DEF tank refill with contaminated fluid or during extreme temperature fluctuations. Technicians often see this code when a non-standard fluid or tap water has been used, … Read more
Diagnostic Code SPN 3226 FMI 10: Meaning and Fix SPN 3226 FMI 10 indicates an abnormal rate of change in NOx levels at the aftertreatment outlet. Typically, this is detected following a failed or incomplete DPF regeneration cycle, where the NOx sensor output shows erratic behavior. Technicians often find this fault after a recent ECM … Read more
Diagnostic Code SPN 3031 FMI 9: Meaning and Fix This fault indicates the diesel exhaust fluid temperature sensor in the storage tank is transmitting data at irregular intervals outside ECM specifications. Technicians commonly encounter this code during winter operations when DEF systems experience thermal cycling stress, particularly after vehicles sit overnight in sub-zero temperatures. The … Read more
Diagnostic Code SPN 6918 FMI 7: Meaning and Fix SPN 6918 with FMI 7 indicates a mechanical system not responding properly due to the SCR System Cleaning Inhibit Switch. This fault is often encountered after a failed attempt to initiate an SCR system cleaning event, particularly when operators inadvertently activate the inhibit switch. In practice, … Read more
Diagnostic Code SPN 3720 FMI 15: Meaning and Fix This fault indicates the Diesel Particulate Filter ash load has exceeded 100% of the target service interval. The ECM calculates ash accumulation based on oil consumption and regeneration history. In practice, this code commonly appears after a forced DPF regeneration fails to reduce ash, or when … Read more