Diesel Diagnostics
SPN & FMI Diesel Fault Codes
Look up SPN and FMI diesel fault codes, common causes, severity and the first checks to make before replacing parts. Every entry here was written from shop-floor diagnosis, not copied off a code list.
The reference is free. The diagnosis is Pro.
Every SPN and FMI page on this site stays open — no account needed. Pro members can take the code into Truck Commander Pro AI with the VIN, symptoms and photos, keep per-truck history, and print a work order. $9.99 a month.
How to read an SPN/FMI code
A J1939 fault is two numbers. The SPN names the parameter the module is watching — a sensor, a circuit, a pressure, a temperature. The FMI names the failure mode: shorted high, shorted low, open circuit, erratic data, not plausible, above or below normal range. Same SPN with a different FMI is a different repair. Read both before you touch a wrench, and pull the whole code set so you know which fault came first.
Need help walking a live truck? Truck Commander Pro AI diagnostic support takes the code, the engine and the symptoms and gives you the test sequence.
The reference is free. The diagnosis is Pro.
Every SPN and FMI page on this site stays open — no account needed. Pro members can take the code into Truck Commander Pro AI with the VIN, symptoms and photos, keep per-truck history, and print a work order. $9.99 a month.
All makes fault codes
- SPN 46 FMI 1Air system pressure critically low
- SPN 84 FMI 19Wheel speed data missing
- SPN 98 FMI 1Engine oil level low
- SPN 168 FMI 1Battery voltage low
- SPN 177 FMI 0Transmission oil temperature too high
- SPN 191 FMI 2Transmission output speed erratic
- SPN 629 FMI 12Engine controller internal fault
- SPN 639 FMI 2J1939 data link error
- SPN 1231 FMI 9Missing message from the transmission
- SPN 1761 FMI 1DEF tank level low
International fault codes
- SPN 51 FMI 7EGR throttle valve not responding
- SPN 91 FMI 3Accelerator pedal position sensor voltage high
- SPN 94 FMI 1Fuel delivery pressure below normal
- SPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal
- SPN 100 FMI 1Engine oil pressure below normal - most severe
- SPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal
- SPN 100 FMI 18Oil pressure below critical
- SPN 102 FMI 4Boost pressure sensor circuit voltage below normal
- SPN 102 FMI 16Boost pressure above normal - moderately severe
- SPN 105 FMI 0Intake manifold air temperature above normal - most severe
- SPN 110 FMI 0Engine coolant temperature above normal - most severe
- SPN 111 FMI 1Coolant level low
- SPN 157 FMI 18Injector metering rail 1 pressure below normal - moderately severe
- SPN 168 FMI 17Battery potential / power input low - least severe
- SPN 190 FMI 0Engine speed above normal - most severe
- SPN 411 FMI 2EGR differential pressure data erratic
- SPN 412 FMI 0EGR temperature above normal - most severe
- SPN 629 FMI 12Engine control module internal fault
- SPN 636 FMI 8Engine position (camshaft) sensor abnormal signal
- SPN 637 FMI 8Crankshaft position sensor abnormal signal
- SPN 639 FMI 9J1939 network abnormal update rate
- SPN 641 FMI 7VGT / turbo actuator not responding to commands
- SPN 651 FMI 5Injector cylinder 1 circuit open
- SPN 652 FMI 5Injector cylinder 2 circuit open
- SPN 653 FMI 5Injector cylinder 3 circuit open
- SPN 654 FMI 5Injector cylinder 4 circuit open
- SPN 655 FMI 5Injector cylinder 5 circuit open
- SPN 656 FMI 5Injector cylinder 6 circuit open
- SPN 1172 FMI 4Turbo inlet temperature sensor low
- SPN 2791 FMI 7EGR valve control not responding to commands
- SPN 3031 FMI 3DEF tank temperature sensor circuit voltage high
- SPN 3050 FMI 18SCR catalyst conversion efficiency below normal
- SPN 3216 FMI 20Inlet NOx sensor drifted
- SPN 3226 FMI 20SCR outlet NOx sensor data drifted high
- SPN 3242 FMI 3DPF inlet temperature sensor circuit voltage high
- SPN 3251 FMI 16DPF restriction above normal
- SPN 3361 FMI 5DEF dosing unit circuit open
- SPN 3364 FMI 2DEF quality poor / data erratic
- SPN 3510 FMI 3Sensor supply voltage 1 high
- SPN 3556 FMI 7Aftertreatment fuel doser not responding
- SPN 3719 FMI 15DPF soot load high - least severe
- SPN 3720 FMI 16DPF ash load high - moderately severe
- SPN 4094 FMI 31NOx conversion inducement - severe derate active
- SPN 5246 FMI 15SCR inducement level 1
- SPN 5394 FMI 5DEF dosing valve circuit open
- SPN 5571 FMI 7High-pressure fuel rail relief valve open
Volvo fault codes
- SPN 84 FMI 2Vehicle speed sensor erratic
- SPN 91 FMI 3Accelerator pedal position sensor voltage high
- SPN 94 FMI 1Fuel delivery pressure below normal
- SPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal
- SPN 100 FMI 1Engine oil pressure low
- SPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal
- SPN 102 FMI 4Boost pressure sensor circuit voltage below normal
- SPN 102 FMI 16Boost pressure above normal - moderately severe
- SPN 105 FMI 0Intake manifold air temperature above normal - most severe
- SPN 110 FMI 0Coolant temperature above limit
- SPN 111 FMI 1Engine coolant level below normal - most severe
- SPN 157 FMI 18Injector rail pressure below spec
- SPN 168 FMI 17Battery potential / power input low - least severe
- SPN 190 FMI 0Engine speed above normal - most severe
- SPN 411 FMI 2EGR differential pressure data erratic
- SPN 411 FMI 3EGR differential pressure sensor high
- SPN 412 FMI 0EGR temperature above normal - most severe
- SPN 629 FMI 12Engine control module internal fault
- SPN 636 FMI 8Engine position (camshaft) sensor abnormal signal
- SPN 637 FMI 8Crankshaft position sensor abnormal signal
- SPN 639 FMI 9J1939 network abnormal update rate
- SPN 641 FMI 7VGT / turbo actuator not responding to commands
- SPN 651 FMI 5Injector cylinder 1 circuit open
- SPN 652 FMI 5Injector cylinder 2 circuit open
- SPN 653 FMI 5Injector cylinder 3 circuit open
- SPN 654 FMI 5Injector cylinder 4 circuit open
- SPN 655 FMI 5Injector cylinder 5 circuit open
- SPN 656 FMI 5Injector cylinder 6 circuit open
- SPN 1127 FMI 16Turbo boost pressure high
- SPN 1172 FMI 4Turbocharger compressor inlet temperature sensor voltage low
- SPN 2791 FMI 7EGR valve not responding
- SPN 3031 FMI 3DEF tank temperature sensor circuit voltage high
- SPN 3050 FMI 18SCR catalyst conversion efficiency below normal
- SPN 3216 FMI 20SCR inlet NOx sensor data drifted high
- SPN 3226 FMI 20Outlet NOx sensor drift
- SPN 3242 FMI 3DPF inlet temperature sensor circuit voltage high
- SPN 3251 FMI 0DPF outlet pressure extremely high
- SPN 3251 FMI 16DPF differential pressure above normal - moderately severe
- SPN 3361 FMI 5DEF dosing unit circuit open
- SPN 3364 FMI 2DEF quality below threshold
- SPN 3556 FMI 7Aftertreatment fuel doser not responding
- SPN 3719 FMI 15DPF soot load high - least severe
- SPN 3719 FMI 16DPF soot load high
- SPN 3720 FMI 16DPF ash load high - moderately severe
- SPN 4094 FMI 31NOx conversion inducement - severe derate active
- SPN 5246 FMI 0Aftertreatment SCR operator inducement severe
- SPN 5394 FMI 5DEF dosing valve circuit open
- SPN 5571 FMI 7High-pressure fuel rail relief valve open
CAT fault codes
- SPN 91 FMI 3Throttle position sensor high
- SPN 94 FMI 1Fuel pressure low
- SPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal
- SPN 100 FMI 1Low engine oil pressure
- SPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal
- SPN 102 FMI 4Boost pressure sensor circuit voltage below normal
- SPN 102 FMI 16Boost pressure above normal - moderately severe
- SPN 105 FMI 0Intake manifold air temperature high
- SPN 110 FMI 0High coolant temperature
- SPN 111 FMI 1Engine coolant level below normal - most severe
- SPN 157 FMI 18Injector metering rail 1 pressure below normal - moderately severe
- SPN 168 FMI 17Battery potential / power input low - least severe
- SPN 172 FMI 3Intake air temperature sensor circuit high
- SPN 190 FMI 0Engine speed above normal - most severe
- SPN 411 FMI 2EGR differential pressure data erratic
- SPN 412 FMI 0EGR temperature above normal - most severe
- SPN 629 FMI 12Engine control module internal fault
- SPN 636 FMI 8Engine position (camshaft) sensor abnormal signal
- SPN 637 FMI 8Crankshaft position sensor abnormal signal
- SPN 639 FMI 9J1939 network abnormal update rate
- SPN 641 FMI 7VGT / turbo actuator not responding to commands
- SPN 651 FMI 5Injector cylinder 1 circuit open
- SPN 652 FMI 5Injector cylinder 2 circuit open
- SPN 653 FMI 5Injector cylinder 3 circuit open
- SPN 654 FMI 5Injector cylinder 4 circuit open
- SPN 655 FMI 5Injector cylinder 5 circuit open
- SPN 656 FMI 5Injector cylinder 6 circuit open
- SPN 1172 FMI 4Turbocharger compressor inlet temperature sensor voltage low
- SPN 1636 FMI 16Intake manifold temperature above warning
- SPN 2791 FMI 7EGR valve control not responding to commands
- SPN 3031 FMI 3DEF tank temperature sensor circuit voltage high
- SPN 3050 FMI 18SCR catalyst conversion efficiency below normal
- SPN 3216 FMI 20SCR inlet NOx sensor data drifted high
- SPN 3226 FMI 20SCR outlet NOx sensor data drifted high
- SPN 3242 FMI 3DPF inlet temperature sensor circuit voltage high
- SPN 3251 FMI 16DPF differential pressure above normal - moderately severe
- SPN 3361 FMI 5DEF dosing unit circuit open
- SPN 3364 FMI 2DEF quality poor / data erratic
- SPN 3556 FMI 7Aftertreatment fuel doser not responding
- SPN 3719 FMI 15DPF soot load high - least severe
- SPN 3720 FMI 16DPF ash load high - moderately severe
- SPN 4094 FMI 31NOx conversion inducement - severe derate active
- SPN 5394 FMI 5DEF dosing valve circuit open
- SPN 5571 FMI 7High-pressure fuel rail relief valve open
Detroit fault codes
- SPN 91 FMI 3Accelerator pedal position sensor voltage high
- SPN 94 FMI 1Fuel delivery pressure below normal
- SPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal
- SPN 100 FMI 1Engine oil pressure below normal - most severe
- SPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal
- SPN 102 FMI 4Boost pressure sensor circuit voltage below normal
- SPN 102 FMI 16Boost pressure above normal - moderately severe
- SPN 105 FMI 0Intake manifold air temperature above normal - most severe
- SPN 110 FMI 0Engine coolant temperature above normal - most severe
- SPN 111 FMI 1Engine coolant level below normal - most severe
- SPN 157 FMI 18Injector metering rail 1 pressure below normal - moderately severe
- SPN 168 FMI 17Battery potential / power input low - least severe
- SPN 190 FMI 0Engine speed above normal - most severe
- SPN 411 FMI 2EGR differential pressure data erratic
- SPN 412 FMI 0EGR temperature above normal - most severe
- SPN 629 FMI 12Engine control module internal fault
- SPN 636 FMI 8Engine position (camshaft) sensor abnormal signal
- SPN 637 FMI 8Crankshaft position sensor abnormal signal
- SPN 639 FMI 9J1939 network abnormal update rate
- SPN 641 FMI 7VGT / turbo actuator not responding to commands
- SPN 651 FMI 5Injector cylinder 1 circuit open
- SPN 652 FMI 5Injector cylinder 2 circuit open
- SPN 653 FMI 5Injector cylinder 3 circuit open
- SPN 654 FMI 5Injector cylinder 4 circuit open
- SPN 655 FMI 5Injector cylinder 5 circuit open
- SPN 656 FMI 5Injector cylinder 6 circuit open
- SPN 1172 FMI 4Turbocharger compressor inlet temperature sensor voltage low
- SPN 2791 FMI 7EGR valve control not responding to commands
- SPN 3031 FMI 3DEF tank temperature sensor circuit voltage high
- SPN 3050 FMI 18SCR catalyst conversion efficiency below normal
- SPN 3216 FMI 20SCR inlet NOx sensor data drifted high
- SPN 3226 FMI 20SCR outlet NOx sensor data drifted high
- SPN 3242 FMI 3DPF inlet temperature sensor circuit voltage high
- SPN 3251 FMI 16DPF differential pressure above normal - moderately severe
- SPN 3361 FMI 5DEF dosing unit circuit open
- SPN 3364 FMI 2DEF quality poor / data erratic
- SPN 3556 FMI 7Aftertreatment fuel doser not responding
- SPN 3719 FMI 15DPF soot load high - least severe
- SPN 3720 FMI 16DPF ash load high - moderately severe
- SPN 4094 FMI 31NOx conversion inducement - severe derate active
- SPN 5394 FMI 5DEF dosing valve circuit open
- SPN 5571 FMI 7High-pressure fuel rail relief valve open
PACCAR fault codes
- SPN 91 FMI 3Accelerator pedal position sensor voltage high
- SPN 94 FMI 1Fuel rail pressure too low
- SPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal
- SPN 100 FMI 1Engine oil pressure critically low
- SPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal
- SPN 102 FMI 3Boost pressure sensor circuit high
- SPN 102 FMI 4Boost pressure sensor circuit voltage below normal
- SPN 102 FMI 16Boost pressure above normal - moderately severe
- SPN 105 FMI 0Intake manifold air temperature above normal - most severe
- SPN 110 FMI 0Engine coolant temperature too high
- SPN 111 FMI 1Engine coolant level below normal - most severe
- SPN 157 FMI 18Injector metering rail 1 pressure below normal - moderately severe
- SPN 168 FMI 17Battery potential / power input low - least severe
- SPN 190 FMI 0Engine speed above normal - most severe
- SPN 411 FMI 2EGR differential pressure data erratic
- SPN 412 FMI 0EGR temperature above normal - most severe
- SPN 597 FMI 2Brake switch circuit fault
- SPN 629 FMI 12Engine control module internal fault
- SPN 636 FMI 8Engine position (camshaft) sensor abnormal signal
- SPN 637 FMI 8Crankshaft position sensor abnormal signal
- SPN 639 FMI 9J1939 network abnormal update rate
- SPN 641 FMI 7VGT / turbo actuator not responding to commands
- SPN 651 FMI 5Injector cylinder 1 circuit open
- SPN 652 FMI 5Injector cylinder 2 circuit open
- SPN 653 FMI 5Injector cylinder 3 circuit open
- SPN 654 FMI 5Injector cylinder 4 circuit open
- SPN 655 FMI 5Injector cylinder 5 circuit open
- SPN 656 FMI 5Injector cylinder 6 circuit open
- SPN 1172 FMI 4Turbocharger compressor inlet temperature sensor voltage low
- SPN 1692 FMI 18Turbocharger underboost
- SPN 2659 FMI 7Intake air heater performance
- SPN 2791 FMI 7EGR valve control not responding to commands
- SPN 3031 FMI 3DEF tank temperature sensor circuit voltage high
- SPN 3050 FMI 18SCR catalyst conversion efficiency below normal
- SPN 3216 FMI 20SCR inlet NOx sensor data drifted high
- SPN 3226 FMI 20SCR outlet NOx sensor data drifted high
- SPN 3242 FMI 3DPF inlet temperature sensor circuit voltage high
- SPN 3251 FMI 0DPF differential pressure very high
- SPN 3251 FMI 16DPF differential pressure above normal - moderately severe
- SPN 3361 FMI 5DEF dosing unit circuit open
- SPN 3364 FMI 2DEF quality poor
- SPN 3556 FMI 7Hydrocarbon doser performance
- SPN 3719 FMI 15DPF soot load high - least severe
- SPN 3719 FMI 16Soot load high (level 1)
- SPN 3720 FMI 16DPF ash load high - moderately severe
- SPN 3936 FMI 31Aftertreatment system incomplete regeneration
- SPN 4094 FMI 31NOx conversion inducement - severe derate active
- SPN 5394 FMI 5DEF dosing valve circuit open
- SPN 5571 FMI 7High-pressure fuel rail relief valve open
MERCEDES fault codes
- SPN 91 FMI 3Accelerator pedal position sensor voltage high
- SPN 94 FMI 1Fuel delivery pressure below normal
- SPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal
- SPN 100 FMI 1Engine oil pressure below normal - most severe
- SPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal
- SPN 102 FMI 4Boost pressure sensor circuit voltage below normal
- SPN 102 FMI 16Boost pressure above normal - moderately severe
- SPN 105 FMI 0Intake manifold air temperature above normal - most severe
- SPN 110 FMI 0Engine coolant temperature above normal - most severe
- SPN 111 FMI 1Engine coolant level below normal - most severe
- SPN 157 FMI 18Injector metering rail 1 pressure below normal - moderately severe
- SPN 168 FMI 17Battery potential / power input low - least severe
- SPN 190 FMI 0Engine speed above normal - most severe
- SPN 411 FMI 2EGR differential pressure data erratic
- SPN 412 FMI 0EGR temperature above normal - most severe
- SPN 629 FMI 12Engine control module internal fault
- SPN 636 FMI 8Engine position (camshaft) sensor abnormal signal
- SPN 637 FMI 8Crankshaft position sensor abnormal signal
- SPN 639 FMI 9J1939 network abnormal update rate
- SPN 641 FMI 7VGT / turbo actuator not responding to commands
- SPN 651 FMI 5Injector cylinder 1 circuit open
- SPN 652 FMI 5Injector cylinder 2 circuit open
- SPN 653 FMI 5Injector cylinder 3 circuit open
- SPN 654 FMI 5Injector cylinder 4 circuit open
- SPN 655 FMI 5Injector cylinder 5 circuit open
- SPN 656 FMI 5Injector cylinder 6 circuit open
- SPN 1172 FMI 4Turbocharger compressor inlet temperature sensor voltage low
- SPN 2791 FMI 7EGR valve control not responding to commands
- SPN 3031 FMI 3DEF tank temperature sensor circuit voltage high
- SPN 3050 FMI 18SCR catalyst conversion efficiency below normal
- SPN 3216 FMI 20SCR inlet NOx sensor data drifted high
- SPN 3226 FMI 20SCR outlet NOx sensor data drifted high
- SPN 3242 FMI 3DPF inlet temperature sensor circuit voltage high
- SPN 3251 FMI 16DPF differential pressure above normal - moderately severe
- SPN 3361 FMI 5DEF dosing unit circuit open
- SPN 3364 FMI 2DEF quality poor / data erratic
- SPN 3556 FMI 7Aftertreatment fuel doser not responding
- SPN 3719 FMI 15DPF soot load high - least severe
- SPN 3720 FMI 16DPF ash load high - moderately severe
- SPN 4094 FMI 31NOx conversion inducement - severe derate active
- SPN 5394 FMI 5DEF dosing valve circuit open
- SPN 5571 FMI 7High-pressure fuel rail relief valve open
Mack fault codes
- SPN 91 FMI 3Accelerator pedal position sensor voltage high
- SPN 94 FMI 1Fuel delivery pressure below normal
- SPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal
- SPN 94 FMI 17Fuel delivery pressure low
- SPN 100 FMI 1Engine oil pressure below normal - most severe
- SPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal
- SPN 102 FMI 4Boost pressure sensor circuit voltage below normal
- SPN 102 FMI 16Boost pressure above normal - moderately severe
- SPN 105 FMI 0Intake manifold air temperature above normal - most severe
- SPN 108 FMI 2Barometric pressure sensor erratic
- SPN 110 FMI 0Engine coolant temperature above normal - most severe
- SPN 111 FMI 1Engine coolant level below normal - most severe
- SPN 157 FMI 18Injector metering rail 1 pressure below normal - moderately severe
- SPN 168 FMI 17Battery potential / power input low - least severe
- SPN 171 FMI 4Ambient air temperature sensor low
- SPN 190 FMI 0Engine overspeed
- SPN 411 FMI 2EGR differential pressure data erratic
- SPN 412 FMI 0EGR temperature above normal - most severe
- SPN 629 FMI 12Engine control module internal fault
- SPN 636 FMI 8Engine position (camshaft) sensor abnormal signal
- SPN 637 FMI 8Crankshaft position sensor abnormal signal
- SPN 639 FMI 9J1939 network abnormal update rate
- SPN 641 FMI 7VGT / turbo actuator not responding to commands
- SPN 651 FMI 5Injector 1 circuit open
- SPN 652 FMI 5Injector cylinder 2 circuit open
- SPN 653 FMI 5Injector cylinder 3 circuit open
- SPN 654 FMI 5Injector cylinder 4 circuit open
- SPN 655 FMI 5Injector cylinder 5 circuit open
- SPN 656 FMI 5Injector cylinder 6 circuit open
- SPN 1172 FMI 4Turbocharger compressor inlet temperature sensor voltage low
- SPN 2791 FMI 7EGR valve control not responding to commands
- SPN 3031 FMI 3DEF tank temperature sensor circuit voltage high
- SPN 3050 FMI 18SCR catalyst conversion efficiency below normal
- SPN 3216 FMI 20SCR inlet NOx sensor data drifted high
- SPN 3226 FMI 20SCR outlet NOx sensor data drifted high
- SPN 3242 FMI 3DPF inlet temperature sensor circuit voltage high
- SPN 3251 FMI 2DPF pressure data erratic with high restriction
- SPN 3251 FMI 16DPF differential pressure above normal - moderately severe
- SPN 3361 FMI 5DEF dosing unit circuit open
- SPN 3364 FMI 2DEF quality poor / data erratic
- SPN 3556 FMI 7Aftertreatment fuel doser not responding
- SPN 3719 FMI 15DPF soot load high - least severe
- SPN 3720 FMI 16DPF ash load high - moderately severe
- SPN 4094 FMI 31NOx conversion inducement - severe derate active
- SPN 4364 FMI 18SCR conversion efficiency low
- SPN 5394 FMI 5DEF dosing valve circuit open
- SPN 5571 FMI 7High-pressure fuel rail relief valve open
Cummins fault codes
- SPN 91 FMI 3Accelerator pedal position sensor voltage high
- SPN 94 FMI 1Fuel delivery pressure below normal
- SPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal
- SPN 100 FMI 1Engine oil pressure below normal - most severe
- SPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal
- SPN 102 FMI 4Boost pressure sensor circuit voltage below normal
- SPN 102 FMI 16Boost pressure above normal - moderately severe
- SPN 105 FMI 0Intake manifold air temperature above normal - most severe
- SPN 110 FMI 0Engine coolant temperature above normal - most severe
- SPN 111 FMI 1Engine coolant level below normal - most severe
- SPN 157 FMI 18Injector metering rail 1 pressure below normal - moderately severe
- SPN 168 FMI 17Battery potential / power input low - least severe
- SPN 190 FMI 0Engine speed above normal - most severe
- SPN 411 FMI 2EGR differential pressure data erratic
- SPN 412 FMI 0EGR temperature above normal - most severe
- SPN 629 FMI 12Engine control module internal fault
- SPN 636 FMI 8Engine position (camshaft) sensor abnormal signal
- SPN 637 FMI 8Crankshaft position sensor abnormal signal
- SPN 639 FMI 9J1939 network abnormal update rate
- SPN 641 FMI 7VGT / turbo actuator not responding to commands
- SPN 651 FMI 5Injector cylinder 1 circuit open
- SPN 652 FMI 5Injector cylinder 2 circuit open
- SPN 653 FMI 5Injector cylinder 3 circuit open
- SPN 654 FMI 5Injector cylinder 4 circuit open
- SPN 655 FMI 5Injector cylinder 5 circuit open
- SPN 656 FMI 5Injector cylinder 6 circuit open
- SPN 1172 FMI 4Turbocharger compressor inlet temperature sensor voltage low
- SPN 2791 FMI 7EGR valve control not responding to commands
- SPN 3031 FMI 3DEF tank temperature sensor circuit voltage high
- SPN 3050 FMI 18SCR catalyst conversion efficiency below normal
- SPN 3216 FMI 20SCR inlet NOx sensor data drifted high
- SPN 3226 FMI 20SCR outlet NOx sensor data drifted high
- SPN 3242 FMI 3DPF inlet temperature sensor circuit voltage high
- SPN 3251 FMI 16DPF differential pressure above normal - moderately severe
- SPN 3361 FMI 5DEF dosing unit circuit open
- SPN 3364 FMI 2DEF quality poor / data erratic
- SPN 3556 FMI 7Aftertreatment fuel doser not responding
- SPN 3719 FMI 15DPF soot load high - least severe
- SPN 3720 FMI 16DPF ash load high - moderately severe
- SPN 4094 FMI 31NOx conversion inducement - severe derate active
- SPN 5394 FMI 5DEF dosing valve circuit open
- SPN 5571 FMI 7High-pressure fuel rail relief valve open
Fault code questions
- What does SPN mean on a diesel fault code?
- SPN stands for Suspect Parameter Number. It is the J1939 number that identifies which component, circuit or measured value the control module is unhappy with — for example SPN 3251 is DPF differential pressure.
- What does FMI mean?
- FMI stands for Failure Mode Identifier. It describes how the value failed: shorted high, shorted low, open circuit, data erratic, data not plausible, or above/below normal range. The FMI is what tells you whether you are chasing wiring or a real physical condition.
- Is a fault code enough to order a part?
- No. A code names a circuit, not a failed part. Verify the reading with live data and a meter before anything gets replaced. That is the whole reason this reference lists tests instead of parts.
Engine-specific lookups
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