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Truck fault code lookup (SPN / FMI)

Truck throwing a fault code? Look up 346+ heavy-duty SPN/FMI and OBD (P-code) faults, then get a mechanic dispatched. Plain-English meanings, how serious it is, the most-likely causes, and what to check first — for Cummins, Detroit, PACCAR, Volvo, Mack, and more.

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Search 346 codes — by code, system, or symptom

SPN 3251 · FMI 2Serious

DPF Differential Pressure — Data Erratic

Aftertreatment (DPF)

SPN 3361 · FMI 7Serious

DEF Dosing Unit — Not Responding Properly

Aftertreatment (SCR/DEF)

SPN 5246 · FMI 0Critical

SCR Operator Inducement — Severe Derate Active

Aftertreatment (SCR/DEF)

SPN 1569 · FMI 31Serious

Engine Protection — Power Derate Active

Engine protection

SPN 100 · FMI 1Critical

Engine Oil Pressure — Extremely Low

SPN 110 · FMI 0Serious

Engine Coolant Temperature — Too High

SPN 627 · FMI 2Serious

ECU Power Supply — Intermittent / Erratic

Electrical / ECU power

SPN 639 · FMI 2Caution

J1939 Data Link — Communication Error

Network / J1939 datalink

SPN 1761 · FMI 1Caution

DEF Tank Level — Low

Aftertreatment (SCR/DEF)

SPN 4364 · FMI 18Serious

SCR Conversion Efficiency — Below Threshold

Aftertreatment (SCR/DEF)

SPN 4094 · FMI 31Serious

DEF Quality — Out of Spec

Aftertreatment (SCR/DEF)

SPN 102 · FMI 3Caution

Boost Pressure Sensor — Voltage High

Air intake / turbo

SPN 3719 · FMI 16Caution

DPF Soot Load — High (Regen Needed)

Aftertreatment (DPF)

SPN 3216 · FMI 20Caution

Inlet (Upstream) NOx Sensor — Data Drifted

Aftertreatment (SCR/DEF)

SPN 94 · FMI 1Serious

Fuel Delivery Pressure — Low

SPN 157 · FMI 18Serious

Injection Rail Pressure — Below Normal

Fuel system (high-pressure)

SPN 411 · FMI 3Caution

EGR Differential Pressure — Voltage High

EGR / air handling

SPN 412 · FMI 0Serious

EGR Temperature — Too High

SPN 97 · FMI 16Caution

Water in Fuel — Detected

SPN 168 · FMI 18Serious

Battery / Charging Voltage — Low

Electrical / charging

SPN 84 · FMI 19Caution

Vehicle Speed Signal — Erratic / Lost

Network / ABS / speed sensor

SPN 105 · FMI 0Serious

Intake Manifold (Charge Air) Temp — High

Air intake / cooling

SPN 1127 · FMI 16Serious

Turbo Boost Pressure — High / Overboost

Air intake / turbo

SPN 5394 · FMI 7Serious

DEF Dosing Valve — Not Responding

Aftertreatment (SCR/DEF)

SPN 629 · FMI 12Serious

Engine Controller (ECM) — Internal Fault

Electrical / ECU

SPN 84 · FMI 2Caution

Vehicle Speed Sensor Erratic

SPN 100 · FMI 3Serious

Oil pressure sensor — voltage high

SPN 100 · FMI 4Serious

Oil pressure sensor — voltage low

SPN 102 · FMI 0Serious

Boost pressure high

SPN 102 · FMI 4Serious

Boost sensor — voltage low

SPN 105 · FMI 3Serious

Intake manifold temp — voltage high

SPN 105 · FMI 4Serious

Intake manifold temp — voltage low

SPN 110 · FMI 3Serious

Coolant temp sensor — voltage high

SPN 110 · FMI 4Serious

Coolant temp sensor — voltage low

SPN 110 · FMI 16Serious

Coolant temperature — moderately high

SPN 111 · FMI 1Critical

Coolant level — low

SPN 160 · FMI 2Serious

Main shaft speed erratic

SPN 161 · FMI 2Serious

Input shaft speed erratic

SPN 162 · FMI 2Serious

Transmission output retarder speed erratic

SPN 164 · FMI 1Serious

Injection control pressure low (HEUI — older engines)

SPN 168 · FMI 17Serious

Battery voltage low during crank

SPN 174 · FMI 16Serious

Fuel temperature high

SPN 177 · FMI 0Serious

Trans oil temperature very high

SPN 177 · FMI 3Serious

Trans oil temperature voltage high

SPN 177 · FMI 4Serious

Trans oil temperature voltage low

SPN 190 · FMI 2Serious

Engine speed sensor — erratic

SPN 190 · FMI 9Serious

Engine speed signal abnormal update rate

SPN 190 · FMI 16Serious

Engine overspeed

SPN 191 · FMI 2Serious

Transmission output shaft speed erratic

SPN 191 · FMI 8Serious

Output shaft speed abnormal

SPN 191 · FMI 9Serious

Output shaft speed not updating (J1939)

SPN 411 · FMI 0Serious

EGR diff pressure high

SPN 411 · FMI 2Serious

EGR diff pressure — erratic

SPN 519 · FMI 4Serious

Service brake air pressure — primary circuit low

SPN 520 · FMI 4Serious

Service brake air pressure — secondary circuit low

SPN 560 · FMI 14Informational

Transmission requests clutch open

SPN 625 · FMI 9Serious

J1939 proprietary datalink lost

SPN 641 · FMI 7Serious

VGT actuator — not responding

SPN 647 · FMI 3Serious

Fan drive — voltage high

SPN 647 · FMI 4Serious

Fan drive voltage low

SPN 651 · FMI 5Serious

Injector #1 open circuit

SPN 652 · FMI 5Serious

Injector #2 open circuit

SPN 653 · FMI 5Serious

Injector #3 open circuit

SPN 654 · FMI 5Serious

Injector #4 open circuit

SPN 655 · FMI 5Serious

Injector #5 open circuit

SPN 656 · FMI 5Serious

Injector #6 open circuit

SPN 723 · FMI 8Serious

Cam position sensor — abnormal signal

SPN 729 · FMI 3Serious

Intake air heater voltage high

SPN 749 · FMI 7Serious

Gear selection failure

SPN 751 · FMI 7Serious

Countershaft brake — not responding

SPN 753 · FMI 2Serious

Range shift signal erratic

SPN 787 · FMI 7Serious

Shift finger not moving to commanded position

SPN 788 · FMI 5Serious

Clutch actuator open circuit

SPN 788 · FMI 6Serious

Clutch actuator short to ground

SPN 788 · FMI 7Serious

Clutch actuator not responding mechanically

SPN 789 · FMI 2Serious

Left front wheel speed sensor erratic

SPN 789 · FMI 8Serious

Left front wheel speed abnormal signal

SPN 790 · FMI 2Serious

Right front wheel speed sensor erratic

SPN 790 · FMI 8Serious

Right front wheel speed abnormal

SPN 791 · FMI 2Serious

Left rear (LF drive) wheel speed erratic

SPN 791 · FMI 8Serious

Left rear wheel speed abnormal

SPN 792 · FMI 2Serious

Right rear wheel speed erratic

SPN 792 · FMI 8Serious

Right rear wheel speed abnormal

SPN 793 · FMI 2Serious

Left tag/pusher wheel speed erratic

SPN 793 · FMI 11Serious

Shift lever — root cause unknown

SPN 794 · FMI 2Serious

Right tag/pusher wheel speed erratic

SPN 795 · FMI 7Serious

Inertia brake not responding

SPN 797 · FMI 5Serious

Modulator valve — left front — open

SPN 797 · FMI 6Serious

Modulator valve — left front — short to ground

SPN 798 · FMI 5Serious

Modulator valve — right front — open

SPN 798 · FMI 6Serious

Right front modulator — short to ground

SPN 799 · FMI 5Serious

Modulator valve — left rear — open

SPN 799 · FMI 6Serious

Left rear modulator — short to ground

SPN 800 · FMI 5Serious

Modulator valve — right rear — open

SPN 800 · FMI 6Serious

Right rear modulator — short to ground

SPN 896 · FMI 7Serious

Transmission range valve not responding

SPN 898 · FMI 2Serious

Gear selector lever erratic

SPN 923 · FMI 2Serious

Reverse switch erratic

SPN 924 · FMI 2Serious

Drive position switch erratic

SPN 973 · FMI 5Serious

Engine retarder enable — open circuit

SPN 974 · FMI 7Serious

ATC (automatic traction control) diff brake — not responding

SPN 1127 · FMI 0Serious

Turbo boost pressure high

SPN 1172 · FMI 3Serious

Turbo compressor inlet temp high voltage

SPN 1176 · FMI 3Serious

Turbo compressor inlet pressure — high voltage

SPN 1209 · FMI 2Serious

Exhaust gas pressure sensor erratic

SPN 1209 · FMI 3Serious

Exhaust back pressure sensor — high voltage

SPN 1761 · FMI 18Serious

DEF tank level low

SPN 1762 · FMI 3Serious

Trans oil pressure voltage high

SPN 1762 · FMI 4Serious

Trans oil pressure voltage low

SPN 1807 · FMI 9Serious

Lost J1939 datalink message from VECU

SPN 1811 · FMI 9Serious

Cab controller J1939 message lost

SPN 2791 · FMI 7Serious

EGR valve — not responding

SPN 2795 · FMI 7Serious

VGT actuator position — not responding

SPN 2919 · FMI 2Serious

Transmission output retarder position erratic

SPN 2920 · FMI 7Serious

Retarder not responding

SPN 3031 · FMI 3Serious

DEF tank temp sensor — voltage high

SPN 3216 · FMI 2Serious

SCR inlet NOx sensor — erratic

SPN 3216 · FMI 9Serious

Upstream NOx sensor — abnormal update rate

SPN 3216 · FMI 12Serious

Upstream NOx sensor — internal failure reported

SPN 3224 · FMI 18Caution

SCR NOx conversion efficiency below threshold

SPN 3226 · FMI 2Serious

Downstream NOx sensor — erratic

SPN 3226 · FMI 9Serious

Downstream NOx sensor — abnormal update rate

SPN 3226 · FMI 12Serious

Downstream NOx sensor — internal failure

SPN 3241 · FMI 3Serious

DPF inlet temp sensor — voltage high

SPN 3242 · FMI 2Serious

DPF outlet temp erratic

SPN 3246 · FMI 3Serious

DPF outlet temp sensor — voltage high

SPN 3251 · FMI 0Caution

DPF differential pressure — high (regen required)

SPN 3251 · FMI 3Serious

DPF differential pressure — voltage high

SPN 3251 · FMI 4Serious

DPF differential pressure — voltage low

SPN 3361 · FMI 5Serious

DEF dosing valve solenoid — open circuit

SPN 3361 · FMI 6Serious

DEF dosing valve solenoid — short to ground

SPN 3361 · FMI 11Serious

DEF dosing unit — root cause unknown

SPN 3361 · FMI 31Serious

DEF dosing unit — condition exists

SPN 3363 · FMI 5Serious

DEF tank heater — open circuit

SPN 3363 · FMI 6Serious

DEF tank heater — short to ground

SPN 3364 · FMI 18Caution

DEF concentration below target

SPN 3482 · FMI 3Serious

Fuel shut-off valve — voltage high

SPN 3509 · FMI 4Serious

Sensor supply 1 (5V) — low voltage

SPN 3510 · FMI 4Serious

Sensor supply 2 — low voltage

SPN 3513 · FMI 4Serious

Sensor supply 5 — low voltage

SPN 3700 · FMI 31Informational

DPF active regeneration in progress

SPN 3703 · FMI 31Informational

DPF regeneration inhibited

SPN 3711 · FMI 31Informational

Forced regeneration requested/in progress

SPN 3712 · FMI 15Serious

SCR operator inducement — stage 1 (warning only)

SPN 3712 · FMI 16Caution

SCR inducement — stage 2 (25% torque reduction)

SPN 3712 · FMI 17Caution

SCR inducement — stage 3 (severe torque derate)

SPN 3712 · FMI 18Caution

SCR inducement — stage 3 (severe derate)

SPN 3712 · FMI 31Caution

SCR inducement — condition exists

SPN 3719 · FMI 0Caution

DPF soot load very high — service required

SPN 3719 · FMI 15Serious

DPF soot load high — warning

SPN 3720 · FMI 0Serious

DPF ash load very high — service required

SPN 4334 · FMI 3Serious

DEF pump pressure sensor — voltage high

SPN 4334 · FMI 4Serious

DEF pump pressure sensor — voltage low

SPN 4334 · FMI 18Caution

DEF pump pressure below target

SPN 4335 · FMI 11Serious

DEF pump — root cause unknown

SPN 4374 · FMI 5Serious

DEF pump relay — open

SPN 4376 · FMI 3Serious

DEF dosing unit temperature — voltage high

SPN 4376 · FMI 4Serious

DEF dosing unit temperature — voltage low

SPN 4383 · FMI 5Serious

DEF line heater 1 — open

SPN 4384 · FMI 5Serious

DEF line heater 2 — open

SPN 4385 · FMI 5Serious

DEF line heater 3 — open

SPN 4732 · FMI 2Serious

DEF quality sensor — erratic readings

SPN 4765 · FMI 3Serious

DOC inlet temp sensor — voltage high

SPN 4766 · FMI 3Serious

DOC outlet temp voltage high

SPN 5246 · FMI 16Caution

SCR NOx limit — moderate derate

SPN 5298 · FMI 7Serious

DEF dosing start permission — not responding

SPN 5394 · FMI 5Serious

DEF dosing valve solenoid — open circuit

SPN 5394 · FMI 6Serious

DEF dosing valve solenoid — short to ground

SPN 5571 · FMI 7Serious

VGT position — not responding (similar to 2795)

SPN 5585 · FMI 31Caution

Engine derate active — parent fault

SPN 5742 · FMI 2Serious

DEF quality erratic

SPN 5856 · FMI 3Serious

Turbo turbine inlet temp — high voltage

SPN 5967 · FMI 15Serious

SCR ammonia slip high

B0001Serious

Driver Airbag Deployment Loop Resistance High

B1001Caution

HVAC Control Module Voltage High

B1002Caution

HVAC Control Module Voltage Low

B1004Serious

Blower Motor Circuit Open

B1005Serious

Blower Motor Circuit Short to Ground

B1010Caution

A/C Pressure Sensor Circuit Fault

B1020Informational

Evaporator Temperature Sensor Circuit Fault

B1030Informational

Ambient Air Temperature Sensor Fault

B1040Caution

Air Distribution Actuator Fault

B1041Caution

Temperature Blend Door Actuator Fault

B1050Serious

APU HVAC Communication Fault

B1052Serious

Coolant/Diesel Heater Circuit Fault

C0031Serious

Left Front Wheel Speed Sensor Circuit Low

C0034Serious

Left Front Wheel Speed Sensor Performance

C0035Caution

Right Front Wheel Speed Sensor Circuit

C0045Serious

Left Rear Wheel Speed Sensor Circuit Low

C0046Serious

Left Rear Wheel Speed Sensor Performance

C0050Serious

ABS Pump Motor Relay Circuit

C0060Serious

ABS Solenoid Valve Circuit

C0110Serious

ABS Pump Motor Circuit

C0121Serious

ABS Valve Solenoid Fault

C0131Serious

ABS Pressure Differential Fault

C0245Caution

Wheel Speed Sensor Frequency Error

C0265Serious

ABS EBCM Motor Relay Circuit

C0267Serious

ABS Pump Motor Circuit Open

C0290Serious

ABS Lost Communication with PCM

C0387Caution

Electronic Brake Proportioning Performance

P0016Serious

Crankshaft/Camshaft Correlation Bank 1 Sensor A

P0087Serious

Fuel Rail/System Pressure Too Low

P0088Serious

Fuel Rail/System Pressure Too High

P0093Critical

Fuel System Leak Detected - Large Leak

P0094Serious

Fuel System Leak Detected - Small

P0096Caution

Intake Air Temp Sensor 2 Circuit Range

P0098Caution

Intake Air Temperature Sensor 2 Circuit High Input

P0100Serious

Mass Airflow Sensor Circuit Malfunction

P0101Serious

Mass Airflow Circuit Range/Performance

P0102Serious

Mass Airflow Circuit Low Input

P0103Serious

Mass Airflow Circuit High Input

P0104Caution

Mass Airflow Circuit Intermittent

P0115Caution

Engine Coolant Temperature Sensor 1 Circuit

P0116Caution

Engine Coolant Temperature Sensor Range

P0117Caution

Engine Coolant Temperature Sensor Circuit Low

P0118Caution

Engine Coolant Temperature Sensor Circuit High

P0119Caution

Engine Coolant Temperature Sensor Intermittent

P0128Serious

Coolant Thermostat Below Regulating Temperature

P0129Informational

Barometric Pressure Too Low

P0171Serious

Fuel System Too Lean Bank 1

P0172Caution

Fuel System Too Rich Bank 1

P0174Serious

Fuel System Too Lean Bank 2

P0183Caution

Fuel Temperature Sensor A Circuit High

P0191Serious

Fuel Rail Pressure Sensor Circuit Range/Performance

P0192Serious

Fuel Rail Pressure Sensor Circuit Low

P0193Serious

Fuel Rail Pressure Sensor Circuit High

P0201Serious

Injector Circuit Open Cylinder 1

P0202Serious

Injector Circuit Open Cylinder 2

P0203Serious

Injector Circuit Open Cylinder 3

P0204Serious

Injector Circuit Open Cylinder 4

P0205Serious

Injector Circuit Open Cylinder 5

P0206Serious

Injector Circuit Open Cylinder 6

P0215Critical

Engine Shutoff Solenoid Circuit

P0217Critical

Engine Coolant Over-Temperature Condition

P0219Critical

Engine Overspeed

P0234Serious

Turbocharger Overboost

P0235Caution

Turbocharger Boost Sensor A Circuit

P0237Caution

Turbocharger Boost Sensor A Circuit Low

P0238Caution

Turbocharger Boost Sensor A Circuit High

P0243Serious

Turbocharger Wastegate Solenoid Circuit

P0245Serious

Turbocharger Wastegate Solenoid Low

P0246Serious

Turbocharger Wastegate Solenoid High

P0251Serious

Injection Pump Fuel Metering Control A

P0263Caution

Cylinder 1 Contribution/Balance Fault

Engine/Injectors

P0266Serious

Cylinder 2 Contribution/Balance Fault

P0269Serious

Cylinder 3 Contribution/Balance Fault

P0272Serious

Cylinder 4 Contribution/Balance Fault

P0275Serious

Cylinder 5 Contribution/Balance Fault

P0278Serious

Cylinder 6 Contribution/Balance Fault

P0299Serious

Turbocharger Underboost Condition

P0341Serious

Camshaft Position Sensor Circuit Range

P0380Serious

Glow Plug/Heater Circuit A

P0401Caution

EGR Flow Insufficient Detected

Engine/Emissions

P0420Serious

Catalyst Efficiency Below Threshold

P0430Serious

Catalyst System Efficiency Below Threshold Bank 2

P0480Serious

Fan 1 Control Circuit Malfunction

P0481Serious

Fan 2 Control Circuit Malfunction

P0483Caution

Fan Rationality Check Failure

P0520Caution

Engine Oil Pressure Sensor/Switch Circuit Malfunction

P0521Caution

Engine Oil Pressure Sensor/Switch Range/Performance

P0522Caution

Engine Oil Pressure Sensor/Switch Circuit Low Input

P0523Caution

Engine Oil Pressure Sensor/Switch Circuit High Input

P0524Critical

Engine Oil Pressure Too Low

P0540Serious

Intake Air Heater Circuit Fault

P0541Serious

Intake Air Heater Circuit Low

P0542Serious

Intake Air Heater Circuit High

P0545Caution

Exhaust Gas Temperature Sensor Circuit Low Bank 1

P0549Caution

Exhaust Gas Temperature Sensor Circuit High Bank 2

P0560Serious

System Voltage Malfunction

P0562Serious

System Voltage Low

P0563Serious

System Voltage High

P0615Serious

Starter Relay Circuit Fault

P0616Serious

Starter Relay Circuit Low

P0619Serious

Starter Relay Circuit High

P0620Serious

Generator Control Circuit

P0621Caution

Generator Lamp L Terminal Circuit

P0622Serious

Generator Field F Terminal Circuit

P0625Serious

Generator Field Terminal Circuit Low

P0626Serious

Generator Field Terminal Circuit High

P0694Caution

Fan Control Circuit High

P0695Caution

Fan Control Circuit Low

P0696Caution

Fan Control Circuit Intermittent

P0700Serious

Transmission Control System Malfunction

P0706Serious

Transmission Range Sensor Circuit Range

P0711Serious

Transmission fluid temp sensor erratic

P0712Serious

Trans fluid temp — voltage low

P0713Serious

Trans fluid temp — voltage high

P0715Serious

Input/turbine speed sensor circuit erratic

P0716Serious

Input/turbine speed sensor — range/performance

P0717Serious

Input/turbine speed sensor — no signal

P0720Serious

Output speed sensor circuit erratic

P0721Serious

Output speed sensor — range/performance

P0722Serious

Output speed sensor — no signal

P0730Serious

Incorrect gear ratio

P0731Serious

1st gear ratio incorrect

P0732Serious

2nd gear ratio incorrect

P0733Serious

3rd gear ratio incorrect

P0734Serious

4th gear ratio incorrect

P0735Serious

5th gear ratio incorrect

P0736Serious

Reverse gear ratio incorrect

P0740Serious

Torque converter clutch solenoid circuit

P0741Serious

P0742Serious

P0748Serious

Pressure control solenoid A circuit

P0750Serious

Shift Solenoid A Malfunction

P0751Serious

Shift solenoid A performance

P0755Serious

Shift Solenoid B Malfunction

P0760Serious

Shift Solenoid C Malfunction

P0846Serious

Trans fluid pressure sensor B circuit

P0847Serious

Trans pressure sensor B — voltage low

P0848Serious

Trans pressure sensor B — voltage high

P0960Serious

Line pressure control solenoid circuit

P0962Serious

Pressure control solenoid A — voltage low

P0963Serious

Pressure control solenoid A — voltage high

P1093Critical

HP Fuel Rail Pressure Low During Power Enrichment

P1096Serious

HP Fuel Rail Pressure High During Active Regen

P2002Serious

Diesel Particulate Filter Efficiency Below Threshold

P2003Serious

DPF Ash Accumulation Restriction

P2033Caution

EGT Sensor Circuit Range Bank 1

P2047Serious

Reductant Injector Circuit Open

P2048Serious

Reductant Injector Circuit Low

P2077Caution

EGR Control Circuit Range

P2200Serious

NOx Sensor Circuit Bank 1

P2201Serious

NOx Sensor Circuit Range Bank 1

P2202Serious

NOx Sensor Circuit Low Bank 1

P2203Serious

NOx Sensor Circuit High Bank 1

P2413Serious

EGR System Performance

P2452Caution

DPF Pressure Sensor A Circuit

P2453Caution

DPF Differential Pressure Sensor Range

P2458Caution

DPF Regeneration Duration

P2459Caution

Diesel Particulate Filter Regeneration Frequency

P2460Critical

DPF Soot Accumulation Restriction

P2761Serious

TCC pressure control solenoid circuit

U0001Critical

High Speed CAN Bus Fault

U0010Caution

Medium Speed CAN Communication Bus Fault

U0100Critical

Lost Communication with ECM/PCM

U0101Serious

Lost Communication with TCM

U0103Serious

Lost Communication with Gear Shift Module

U0105Critical

Lost Communication with Fuel Injector Control Module

U0121Serious

Lost comms with ABS

U0122Caution

Lost Communication with Vehicle Dynamics Control Module

U0140Serious

Lost Communication with Body Control Module

U0155Caution

Lost Communication with Instrument Cluster

U0401Serious

Invalid Data from ECM

U0402Serious

Invalid Data from TCM

U0415Serious

Invalid Data from ABS Module

This is general diagnostic guidance, not a substitute for a scan-tool diagnosis on your specific engine. When in doubt, get a qualified mobile diesel tech on the truck.