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Truck fault code lookup (SPN / FMI)

Truck throwing a fault code? Look up 367+ heavy-duty SPN/FMI and OBD (P-code) faults, then find a provider near you. 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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Browse by system

329 of these codes belong to a system big enough to have its own page. Start where the truck is complaining.

Aftertreatment & Emissions
100 codes
The codes that park a truck without anything mechanical breaking: DPF differential pressure, DEF quality and dosing, SCR NOx conversion, EGR flow, valve and cooler faults, and the regen logic tying them together.
Drivetrain & Transmission
61 codes
Codes off the automated manual or automatic: clutch position and actuator faults, shift solenoids, range and splitter problems, driveline and output-shaft speed mismatch, retarder faults, and transmission oil temperature.
Engine
58 codes
The air path and the cylinders: turbo boost and VGT position, intake and charge-air temperature, mass airflow, the intake-air heater and glow plugs, crank and cam position, and the engine-protection logic that pulls power when a reading goes out of range.
Brakes, ABS & Stability
41 codes
ABS, stability and foundation-brake faults — wheel-speed sensors, modulator valves, air pressure, steering-angle and stability inputs, the trailer ABS link, and the wheel-based vehicle speed the ABS ECU broadcasts to the rest of the truck.
Fuel System
39 codes
Tank to injector — lift pump and rail pressure, per-cylinder injector circuits and cylinder balance, water in fuel, and the filters in between.
Electrical, Charging & Network
30 codes
Charging, grounds and the J1939 network: alternator output, battery and sensor-supply voltage, lighting and starter circuits, and every lost-communication code — whichever module dropped off the bus, a U-code is a network fault and is diagnosed at the datalink.

Search every code

Type a code, a system, or a symptom — the box searches all 367 codes, including the ones listed on the system pages above. The four smaller systems are listed in full below.

Cooling (18)

Engine coolant temperature and level, the thermostat, and fan-drive faults — the sensor, the circuit and the over-temp itself, together. The EGR cooler is not here; it sits with the rest of EGR under Aftertreatment. These escalate fast: an overheat code that gets ignored becomes an engine-protection shutdown, not a warning.

SPN 110 · FMI 0Serious
Engine Coolant Temperature — Too High
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
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
P0217Critical
Engine Coolant Over-Temperature Condition
P0480Serious
Fan 1 Control Circuit Malfunction
P0481Serious
Fan 2 Control Circuit Malfunction
P0483Caution
Fan Rationality Check Failure
P0694Caution
Fan Control Circuit High
P0695Caution
Fan Control Circuit Low
P0696Caution
Fan Control Circuit Intermittent

HVAC & Refrigeration (11)

Cab climate and reefer-side refrigeration faults: A/C pressure and compressor clutch, blend doors, blower control, cab heater circuits. Rarely a driveability problem — frequently a load problem when it is the trailer unit.

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

Lubrication (8)

Engine oil pressure, level and temperature, sensor circuit faults included. Low oil pressure is the one fault on this site you never drive on: engine protection may shut the truck down, and if it doesn't, the bearings will finish the job.

SPN 100 · FMI 1Critical
Engine Oil Pressure — Extremely Low
SPN 100 · FMI 3Serious
Oil pressure sensor — voltage high
SPN 100 · FMI 4Serious
Oil pressure sensor — voltage low
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

Chassis, Cab & Body (1)

One code today — the airbag/restraint loop. Suspension, steering, tires and TPMS, fifth wheel, frame and cab-body faults are in the knowledge base but carry bare-alpha code numbers the generator does not route to a page yet, so this section is honestly near-empty rather than padded. Lighting is not here: light circuits are under Electrical.

B0001Serious
Driver Airbag Deployment Loop Resistance High

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.