SAE J1939 SPN and FMI fault codes for automatic and manual transmissions. Covers electronic transmission controllers, transmission fluids, gear selection, torque converter, and driveline diagnostic parameters for commercial vehicles and off-highway equipment.
Diagnostic Code SPN 3359 FMI 8: Meaning and Fix SPN 3359 FMI 8 is triggered when the Transmission Control Module detects an abnormal frequency, pulse width, or period from the transmission oil filter restriction switch signal line. Instead of receiving the expected binary state (00b or 01b), the TCM registers an erratic waveform inconsistent with … Read more
Diagnostic Code SPN 3359 FMI 21: Meaning and Fix SPN 3359 FMI 21 indicates the transmission oil filter restriction switch signal has drifted below the valid low threshold, typically below 0.5 V. This fault commonly appears after a transmission oil change when the switch connector is not fully seated, causing intermittent grounding. The ECM expects … Read more
Diagnostic Code SPN 3359 FMI 20: Meaning and Fix SPN 3359 FMI 20 indicates the transmission oil filter restriction switch signal has drifted abnormally high, exceeding the expected binary threshold monitored by the TCM. Per SAE J1939 PGN Transmission Fluids 2, the switch should report 00b (no restriction) under normal operating conditions. This fault commonly … Read more
Diagnostic Code SPN 3359 FMI 19: Meaning and Fix SPN 3359 FMI 19 indicates a transmission oil filter restriction switch error due to received network data in error. This fault can often surface after a transmission fluid change, where improper sensor calibrations lead to false readings. In practice, technicians might see this code following a … Read more
Diagnostic Code SPN 3359 FMI 17: Meaning and Fix SPN 3359 FMI 17 indicates the transmission oil filter restriction switch sends a signal below the normal operating range, meaning the ECM detects no restriction when one may exist. This fault often appears after a cold start or following an oil change where air entraps in … Read more
Diagnostic Code SPN 3359 FMI 16: Meaning and Fix SPN 3359 FMI 16 activates when the transmission oil filter restriction switch reports a moderately elevated differential pressure, indicating partial clogging above the normal operating threshold. The TCM receives a binary signal state of 01b, confirming active restriction. This fault commonly appears during cold-weather startups on … Read more
Diagnostic Code SPN 3359 FMI 15: Meaning and Fix The SPN 3359 FMI 15 fault indicates a restriction in the transmission oil filter, with data showing above-normal but least severe conditions. This code commonly appears following a scheduled maintenance where the transmission oil filter was not replaced or improperly installed. Technicians often encounter this warning … Read more
Diagnostic Code SPN 3359 FMI 10: Meaning and Fix SPN 3359 FMI 10 indicates the transmission oil filter restriction switch has detected an abnormal rate of change in its signal, meaning the switch transitions between ‘restriction’ and ‘no restriction’ faster than expected by the ECM. This code commonly appears after a forced DPF regeneration when … Read more
Diagnostic Code SPN 781 FMI 9: Meaning and Fix SPN 781, relating to the Transmission Shift Finger Engagement Indicator, signals an abnormal update rate with FMI 9. This often becomes evident after transmission repairs or ECM updates, where the shift finger fails to reach the expected position in a timely manner. Workshop scenarios frequently involve … Read more
Diagnostic Code SPN 781 FMI 18: Meaning and Fix SPN 781 FMI 18 indicates the transmission shift finger engagement sensor is reporting valid data below normal operating parameters. This fault commonly appears during gear selection attempts when the shift finger cannot achieve full mechanical engagement. Technicians frequently encounter this code after transmission overhauls when actuator … Read more