Fault Codes by SPN
SPN is the Suspect Parameter Number — the circuit, sensor or system the ECM is flagging. Pick your SPN to see every failure mode we document for it and what to test first.
Air system pressure critically low
FMI 1 · All makes
SPN 51EGR throttle valve not responding
FMI 7 · International
SPN 84Vehicle speed sensor erratic
FMI 2, 19 · Volvo, All makes
SPN 91Throttle position sensor high
FMI 3 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 94Fuel rail pressure too low
FMI 1, 3, 17 · PACCAR, CAT, Detroit, International, MERCEDES, Volvo, Mack, Cummins
SPN 98Engine oil level low
FMI 1 · All makes
SPN 100Engine oil pressure critically low
FMI 1, 3, 18 · PACCAR, CAT, Volvo, Detroit, International, MERCEDES, Mack, Cummins
SPN 102Boost pressure sensor circuit high
FMI 3, 4, 16 · PACCAR, CAT, Detroit, International, MERCEDES, Volvo, Mack, Cummins
SPN 105Intake manifold air temperature high
FMI 0 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 108Barometric pressure sensor erratic
FMI 2 · Mack
SPN 110Engine coolant temperature too high
FMI 0 · PACCAR, Volvo, CAT, Detroit, International, MERCEDES, Mack, Cummins
SPN 111Coolant level low
FMI 1 · International, CAT, Detroit, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 157Injector rail pressure below spec
FMI 18 · Volvo, CAT, Detroit, International, PACCAR, MERCEDES, Mack, Cummins
SPN 168Battery voltage low
FMI 1, 17 · All makes, CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 171Ambient air temperature sensor low
FMI 4 · Mack
SPN 172Intake air temperature sensor circuit high
FMI 3 · CAT
SPN 177Transmission oil temperature too high
FMI 0 · All makes
SPN 190Engine overspeed
FMI 0 · Mack, CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Cummins
SPN 191Transmission output speed erratic
FMI 2 · All makes
SPN 411EGR differential pressure data erratic
FMI 2, 3 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 412EGR temperature above normal - most severe
FMI 0 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 597Brake switch circuit fault
FMI 2 · PACCAR
SPN 629Engine controller internal fault
FMI 12 · All makes, CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 636Engine position (camshaft) sensor abnormal signal
FMI 8 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 637Crankshaft position sensor abnormal signal
FMI 8 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 639J1939 data link error
FMI 2, 9 · All makes, CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 641VGT / turbo actuator not responding to commands
FMI 7 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 651Injector 1 circuit open
FMI 5 · Mack, CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Cummins
SPN 652Injector cylinder 2 circuit open
FMI 5 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 653Injector cylinder 3 circuit open
FMI 5 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 654Injector cylinder 4 circuit open
FMI 5 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 655Injector cylinder 5 circuit open
FMI 5 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 656Injector cylinder 6 circuit open
FMI 5 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 1127Turbo boost pressure high
FMI 16 · Volvo
SPN 1172Turbo inlet temperature sensor low
FMI 4 · International, CAT, Detroit, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 1231Missing message from the transmission
FMI 9 · All makes
SPN 1636Intake manifold temperature above warning
FMI 16 · CAT
SPN 1692Turbocharger underboost
FMI 18 · PACCAR
SPN 1761DEF tank level low
FMI 1 · All makes
SPN 2659Intake air heater performance
FMI 7 · PACCAR
SPN 2791EGR valve not responding
FMI 7 · Volvo, CAT, Detroit, International, PACCAR, MERCEDES, Mack, Cummins
SPN 3031DEF tank temperature sensor circuit voltage high
FMI 3 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 3050SCR catalyst conversion efficiency below normal
FMI 18 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 3216Inlet NOx sensor drifted
FMI 20 · International, CAT, Detroit, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 3226Outlet NOx sensor drift
FMI 20 · Volvo, CAT, Detroit, International, PACCAR, MERCEDES, Mack, Cummins
SPN 3242DPF inlet temperature sensor circuit voltage high
FMI 3 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 3251DPF differential pressure very high
FMI 0, 2, 16 · PACCAR, Volvo, Mack, International, CAT, Detroit, MERCEDES, Cummins
SPN 3361DEF dosing unit circuit open
FMI 5 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 3364DEF quality poor
FMI 2 · PACCAR, Volvo, CAT, Detroit, International, MERCEDES, Mack, Cummins
SPN 3510Sensor supply voltage 1 high
FMI 3 · International
SPN 3556Hydrocarbon doser performance
FMI 7 · PACCAR, CAT, Detroit, International, MERCEDES, Volvo, Mack, Cummins
SPN 3719DPF soot load high - least severe
FMI 15, 16 · Volvo, CAT, Detroit, International, PACCAR, MERCEDES, Mack, Cummins
SPN 3720DPF ash load high - moderately severe
FMI 16 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 3936Aftertreatment system incomplete regeneration
FMI 31 · PACCAR
SPN 4094NOx conversion inducement - severe derate active
FMI 31 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 4364SCR conversion efficiency low
FMI 18 · Mack
SPN 5246Aftertreatment SCR operator inducement severe
FMI 0, 15 · Volvo, International
SPN 5394DEF dosing valve circuit open
FMI 5 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
SPN 5571High-pressure fuel rail relief valve open
FMI 7 · CAT, Detroit, International, PACCAR, MERCEDES, Volvo, Mack, Cummins
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