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 5024 FMI 20: Meaning and Fix SPN 5024 FMI 20 is triggered when the engine exhaust NOx sensor heater ratio data drifts high, affecting sensor accuracy at the aftertreatment system intake. This fault often appears following a forced DPF regeneration, where temperature fluctuations can stress the sensor. Technicians frequently observe this after … Read more
Diagnostic Code SPN 3222 FMI 8: Meaning and Fix SPN 3222 FMI 8 indicates an abnormal frequency or pulse width in the heater circuit of the exhaust gas sensor in bank 1. This fault commonly arises after forced DPF regeneration due to excessive heat affecting the sensor’s resistance. Technicians often encounter this code following ECM … Read more
Diagnostic Code SPN 3222 FMI 21: Meaning and Fix SPN 3222 FMI 21 indicates the heater element of the exhaust gas sensor (NOx or O2) at aftertreatment intake bank 1 has produced a signal that has drifted below its calibrated operating threshold. The ECM’s sensor control software flags this as a preliminary heater fault. This … Read more
Diagnostic Code SPN 3222 FMI 20: Meaning and Fix SPN 3222 with FMI 20 indicates a data drift high condition in the exhaust gas sensor heater located in exhaust bank 1. This fault code typically appears after a sensor replacement or following an ECM update where recalibration was not performed correctly. Technicians often encounter this … Read more
Diagnostic Code SPN 3222 FMI 19: Meaning and Fix SPN 3222 FMI 19 indicates a controller area network (CAN) data integrity issue specifically related to the exhaust gas sensor 1 heater control message on the Aftertreatment 1 Intake Gas 1 bus. This is not a direct heater electrical fault but a communication failure where the … Read more
Diagnostic Code SPN 3222 FMI 17: Meaning and Fix SPN 3222 FMI 17 identifies that the heater element of the Engine Exhaust Bank 1 Gas Sensor 1 is operating below its normal functional range, classified as least severe per SAE J1939-73. The ECM’s sensor control software detects insufficient heater output, compromising NOx or O2 measurement … Read more
Diagnostic Code SPN 3222 FMI 16: Meaning and Fix SPN 3222 FMI 16 is triggered by the exhaust gas sensor’s heater in bank 1 when its readings exceed normal operating ranges. This fault often appears after a vehicle undergoes major exhaust system overhauls, such as replacing the exhaust manifold or NOx sensor, and can manifest … Read more
Diagnostic Code SPN 3222 FMI 15: Meaning and Fix SPN 3222 FMI 15 indicates the Engine Exhaust 1 Gas Sensor 1 Heater Preliminary FMI has detected a voltage or resistance value above the normal operating range, as defined by the manufacturer’s sensor control software. This is the least severe FMI, but it signals a developing … Read more
Diagnostic Code SPN 3222 FMI 10: Meaning and Fix SPN 3222 FMI 10 indicates the ECM detected an abnormal rate of change in the heater circuit of the exhaust gas sensor (NOx or O2) located upstream of the aftertreatment system on exhaust bank 1. The heater’s thermal ramp-up deviates beyond calibrated thresholds, triggering this fault. … Read more
Diagnostic Code SPN 5743 FMI 8: Meaning and Fix SPN 5743 FMI 8 indicates the Aftertreatment 1 SCR Temperature Sensor Module is transmitting signals with abnormal frequency, pulse width, or period over the J1939 datalink. The ECU cannot correctly interpret multiplexed temperature values from SCR bank 1 sensors. This fault commonly appears after a DEF … Read more