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 788 FMI 7: Meaning and Fix SPN 788 FMI 7 indicates the transmission clutch actuator mechanical system is not responding properly despite receiving correct electrical commands from the ECM. This fault commonly appears during heavy-duty operations when actuator linkages seize or pneumatic cylinders fail, preventing proper clutch engagement/disengagement. Technicians frequently encounter this … Read more
Diagnostic Code SPN 4178 FMI 31: Meaning and Fix SPN 4178 FMI 31 indicates the Electronic Transmission Controller detects a service condition requiring maintenance attention. This fault commonly appears in Mercedes-Benz Atego and MAN TGX units when transmission fluid service intervals exceed manufacturer specifications or after clutch replacement procedures when service counters require manual reset … Read more
Diagnostic Code SPN 191 FMI 9: Meaning and Fix SPN 191 FMI 9 indicates the transmission output shaft speed signal is not being received at the expected update interval by the engine or chassis controller. This fault commonly appears after a transmission control module (TCM) software flash or when a vehicle sits idle for extended … Read more
Diagnostic Code SPN 560 FMI 11: Meaning and Fix Transmission driveline engaged (SPN 560) with FMI 11 suggests an unknown root cause in torque transfer. This issue often occurs after transmission maintenance or ECM replacement. Technicians frequently encounter this fault when the driveline engagement is reported as active, but no discernible torque transfer occurs. It’s … Read more
Diagnostic Code SPN 3359 FMI 31: Meaning and Fix SPN 3359 with FMI 31 indicates a condition exists related to the transmission oil filter restriction switch. This fault often appears after a transmission oil change when technicians forget to replace the oil filter. If overlooked, it can lead to severe transmission damage. In practice, workshops … Read more