J1939 fault codes
Type the code. Get the fix.
Any SPN and FMI from Cat, Deere, Cummins, Komatsu or Volvo. What failed, how urgent, what to check first.
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Fault code lookupJ1939 · 191 SPNs
PART · SPN 3251DPF pressure differenceFAILURE · FMI 0Reading is way too high. Treat it as real until you prove the sensor wrong.
Fix it today
DPF pressure difference is way too high. The filter is heavily loaded with soot or ash, or the sensor reads wrong. The engine will derate.
- Read the soot load.
- Run a parked regen if the machine allows it.
- Check the sensor hoses for soot plugs, cracks or water.
- If regens won't run, the filter may need to come off for cleaning.
Paste the whole line if you like: "SPN 3251 FMI 0", "3251/0" or Deere's "003251.00". Plain-words guidance; the service manual wins.
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3Fault codes, plus what you needFault codes, plus machine hours and repair tickets
Every code, by system
191 SPNs with plain-words meanings. Each page lists its FMIs and what to check first.
EGR
Fuel system
- SPN 38fuel level 2
- SPN 94fuel delivery pressure
- SPN 95fuel filter restriction
- SPN 96fuel level
- SPN 97water in fuel
- SPN 157fuel rail pressure
- SPN 164injection control pressure
- SPN 174fuel temperature
- SPN 633fuel control valve
- SPN 1075electric lift pump
- SPN 1076injection pump fuel control valve
- SPN 1077injection pump controller
- SPN 1239fuel leak
- SPN 1347fuel pump metering valve
- SPN 1349fuel rail 2 pressure
- SPN 1382fuel filter restriction (suction side)
- SPN 5571rail pressure relief valve
- SPN 5585rail pressure while cranking
Brakes and air
- SPN 46air supply pressure
- SPN 70parking brake switch
- SPN 116brake application pressure
- SPN 117brake primary pressure
- SPN 118brake secondary pressure
- SPN 521brake pedal position
- SPN 597brake switch
- SPN 789ABS wheel sensor, axle 1 left
- SPN 790ABS wheel sensor, axle 1 right
- SPN 791ABS wheel sensor, axle 2 left
- SPN 792ABS wheel sensor, axle 2 right
Air intake and turbo
- SPN 51intake throttle position
- SPN 52intercooler temperature
- SPN 102boost pressure
- SPN 103turbo speed
- SPN 104turbo oil pressure
- SPN 105intake manifold temperature
- SPN 106air inlet pressure
- SPN 107air filter restriction
- SPN 108barometric pressure
- SPN 172air inlet temperature
- SPN 641turbo actuator (VGT)
- SPN 1127turbo boost pressure
- SPN 1172turbo compressor inlet temperature
- SPN 1176turbo compressor inlet pressure
- SPN 1180turbo turbine inlet temperature
- SPN 1188turbo wastegate
- SPN 2629turbo compressor outlet temperature
- SPN 2630charge air cooler outlet temperature
- SPN 2795VGT actuator position
- SPN 3464intake throttle actuator
- SPN 3563intake manifold pressure
Engine sensors and protection
- SPN 84wheel-based speed
- SPN 91accelerator pedal position
- SPN 171outside air temperature
- SPN 173exhaust temperature
- SPN 190engine speed
- SPN 558pedal idle switch
- SPN 636camshaft position sensor
- SPN 637crankshaft position sensor
- SPN 644external speed command
- SPN 723engine speed sensor 2
- SPN 974remote throttle
- SPN 1109engine protection: shutdown coming
- SPN 1110engine protection: engine shut down
- SPN 1136ECU temperature
- SPN 1569engine protection derate
Engine oil
Cooling
Batteries and wiring
- SPN 115alternator current
- SPN 158keyswitch battery voltage
- SPN 167charging voltage
- SPN 168battery voltage
- SPN 444battery 2 voltage
- SPN 626cold start aid
- SPN 627computer power supply
- SPN 677starter relay
- SPN 729intake air heater relay
- SPN 1081wait-to-start lamp
- SPN 1485ECU main relay
- SPN 3509sensor supply 1
- SPN 3510sensor supply 2
- SPN 3511sensor supply 3
- SPN 3512sensor supply 4
- SPN 3513sensor supply 5
- SPN 3597ECU output supply voltage
Transmission
Computers and data link
Injectors and misfire
- SPN 651injector cylinder 1
- SPN 652injector cylinder 2
- SPN 653injector cylinder 3
- SPN 654injector cylinder 4
- SPN 655injector cylinder 5
- SPN 656injector cylinder 6
- SPN 1322misfire, several cylinders
- SPN 1323misfire cylinder 1
- SPN 1324misfire cylinder 2
- SPN 1325misfire cylinder 3
- SPN 1326misfire cylinder 4
- SPN 1327misfire cylinder 5
- SPN 1328misfire cylinder 6
- SPN 2797injector group 1
- SPN 2798injector group 2
DPF and regen
- SPN 1209exhaust back pressure
- SPN 3241exhaust temperature 1
- SPN 3242DPF inlet temperature
- SPN 3246DPF outlet temperature
- SPN 3249exhaust temperature 2
- SPN 3251DPF pressure difference
- SPN 3471aftertreatment fuel pressure valve
- SPN 3480aftertreatment fuel pressure
- SPN 3482aftertreatment fuel enable valve
- SPN 3556aftertreatment fuel doser
- SPN 3609DPF inlet pressure
- SPN 3610DPF outlet pressure
- SPN 3695regen inhibit switch
- SPN 3696regen force switch
- SPN 3703regen blocked by switch
- SPN 3719DPF soot load
- SPN 3720DPF ash load
- SPN 3936DPF system
- SPN 4765DOC inlet temperature
- SPN 4766DOC outlet temperature
- SPN 4795DPF missing
- SPN 4796DOC missing
- SPN 5018DOC face plugged
- SPN 5298DOC efficiency
- SPN 5319DPF regen did not finish
- SPN 5397DPF regens too frequent
- SPN 5742DPF temperature sensor module
Hydraulics
DEF and SCR
- SPN 1761DEF tank level
- SPN 3031DEF tank temperature
- SPN 3216intake NOx sensor
- SPN 3226outlet NOx sensor
- SPN 3361DEF dosing unit
- SPN 3362DEF dosing unit lines
- SPN 3363DEF tank heater
- SPN 3364DEF quality
- SPN 3515DEF temperature 2
- SPN 3516DEF concentration
- SPN 4094NOx high: poor DEF quality
- SPN 4095NOx high: DEF dosing stopped
- SPN 4096NOx high: DEF tank empty
- SPN 4334DEF doser pressure
- SPN 4340DEF line heater 1
- SPN 4342DEF line heater 2
- SPN 4344DEF line heater 3
- SPN 4360SCR inlet temperature
- SPN 4363SCR outlet temperature
- SPN 4364SCR efficiency
- SPN 4374DEF pump
- SPN 4376DEF return valve
- SPN 4792SCR catalyst
- SPN 4794SCR catalyst missing
- SPN 5245SCR inducement active
- SPN 5246SCR inducement (derate)
- SPN 5394DEF dosing valve
- SPN 5491DEF line heater relay
- SPN 5745DEF dosing unit heater
- SPN 5746DEF dosing unit heater relay
FMI numbers in plain words
| FMI | Means |
|---|---|
| 0 | above normal, most severe. Reading is way too high. Treat it as real until you prove the sensor wrong. |
| 1 | below normal, most severe. Reading is way too low. Treat it as real until you prove the sensor wrong. |
| 2 | erratic or intermittent. Reading jumps around or doesn't make sense. Often a loose plug, a bad wire, or two sensors that disagree. |
| 3 | voltage high or shorted high. Signal voltage too high. Usually an open wire, a bad plug, or a wire shorted to power. |
| 4 | voltage low or shorted low. Signal voltage too low. Usually a wire shorted to ground or a bad sensor. |
| 5 | current low or open circuit. Too little current. Usually a broken wire, an unplugged connector, or an open coil. |
| 6 | current high or grounded. Too much current. Usually a wire shorted to ground or a shorted coil. |
| 7 | not responding. The part was told to move and didn't. Look for sticking, binding or a seized part. |
| 8 | abnormal frequency or pulse. The signal's pulses are wrong. Common on speed sensors and PWM sensors. |
| 9 | abnormal update rate. Data stopped arriving on time over the network. Check the data link and the module that sends it. |
| 10 | abnormal rate of change. Reading changed faster than is physically possible. Often a bad sensor or a loose connection. |
| 11 | root cause not known. The computer knows something is wrong but can't say what. Check the other active codes. |
| 12 | bad device or component. A smart sensor or module reports that it has failed. |
| 13 | out of calibration. Needs calibrating, or the wrong part or software is installed. Usually a dealer-tool job. |
| 14 | special instructions. The maker uses this for its own meaning. Look it up in the service manual for this machine. |
| 15 | above normal, least severe. A bit high. A warning, not a shutdown yet. |
| 16 | above normal, moderately severe. High enough to matter. Fix it before it gets worse. |
| 17 | below normal, least severe. A bit low. A warning, not a shutdown yet. |
| 18 | below normal, moderately severe. Low enough to matter. Fix it before it gets worse. |
| 19 | network data error. Another module sent bad data over the network. The fault may be in that module, not this one. |
| 20 | drifted high. The reading has crept high over time. Common as a sensor ages. |
| 21 | drifted low. The reading has crept low over time. Common as a sensor ages. |
| 22 | Reserved for SAE assignment. Not assigned by the standard. If you see it, the maker gave it its own meaning. |
| 23 | Reserved for SAE assignment. Not assigned by the standard. If you see it, the maker gave it its own meaning. |
| 24 | Reserved for SAE assignment. Not assigned by the standard. If you see it, the maker gave it its own meaning. |
| 25 | Reserved for SAE assignment. Not assigned by the standard. If you see it, the maker gave it its own meaning. |
| 26 | Reserved for SAE assignment. Not assigned by the standard. If you see it, the maker gave it its own meaning. |
| 27 | Reserved for SAE assignment. Not assigned by the standard. If you see it, the maker gave it its own meaning. |
| 28 | Reserved for SAE assignment. Not assigned by the standard. If you see it, the maker gave it its own meaning. |
| 29 | Reserved for SAE assignment. Not assigned by the standard. If you see it, the maker gave it its own meaning. |
| 30 | Reserved for SAE assignment. Not assigned by the standard. If you see it, the maker gave it its own meaning. |
| 31 | condition exists. The condition the SPN names is happening right now (often a status or a derate). |
Urgency on each code page: Stop the machine, Fix it today, Schedule it.
In the Dozer app · Fault codes
Next time, Dozer catches the code when it fires.
Plug a CAN logger into the machine's J1939 port, or connect the telematics you have. When a code fires, Dozer opens a repair ticket with the meaning, how urgent it is and what to check.
- The code, the machine and its hours on one ticket
- Severity sorted: keep working, plan a stop, or stop now
- The mechanic gets the checklist before they drive out
- Repeat codes on the same machine get flagged
LIVE EX-04 · SPN 3251 FMI 0 · plan a stop today Photo is an AI-generated stand-in, not a customer site.
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Questions crews ask
What is a J1939 fault code?
Diesel engines and machines that speak SAE J1939 report faults as two numbers: the SPN (suspect parameter number) says which part or reading, and the FMI (failure mode identifier, 0 to 31) says how it failed. SPN 3251 FMI 0 means the DPF pressure reading is far too high.
Where do I find the SPN and FMI?
On the machine's display (often under diagnostics or active faults), on a code reader plugged into the 9-pin diagnostic port, or in your telematics (VisionLink, JDLink, Komtrax, CareTrack). Deere writes them as 000100.01: SPN 100, FMI 1.
Do Cat, Deere and Cummins use the same codes?
For standard SPNs (below 520192), yes: SPN 100 is engine oil pressure on all of them. Makers add their own codes above 520192 and their own fix steps, so the service manual wins.
What does the FMI number mean?
FMI 0 and 1 are a reading far above or below normal; 2 is erratic; 3 to 6 are wiring (shorted high or low, open, grounded); 7 is a part not responding; 31 means the condition exists. 32 FMIs in all.
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