SPN 3226: outlet NOx sensor
The NOx sensor after the SCR. Type another SPN and FMI to check it.
The NOx sensor after the SCR. The computer compares it with the inlet sensor to see if the SCR is cleaning the exhaust.
- Check DEF quality with a refractometer.
- Check the DEF doser for crystals.
- Check the sensor plug.
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.
What SPN 3226 means
The NOx sensor after the SCR. The computer compares it with the inlet sensor to see if the SCR is cleaning the exhaust.
How urgent it is
Fix it today. Fix it this shift or today. Left alone it tends to become a derate.
What to check first
- Check DEF quality with a refractometer.
- Check the DEF doser for crystals.
- Check the sensor plug.
Plain-words guidance for a foreman, not a repair procedure. Makers add their own codes and steps; the machine's service manual wins.
Other FMIs for SPN 3226
| Code | What failed | Urgency |
|---|---|---|
| SPN 3226 FMI 2 | erratic or intermittent | Fix it today |
| SPN 3226 FMI 4 | voltage low or shorted low | Fix it today |
| SPN 3226 FMI 9 | abnormal update rate | Fix it today |
| SPN 3226 FMI 10 | abnormal rate of change | Fix it today |
| SPN 3226 FMI 13 | out of calibration | Fix it today |
| SPN 3226 FMI 20 | drifted high | Fix it today |
| SPN 3226 FMI 21 | drifted low | Fix it today |
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 does SPN 3226 mean?
The NOx sensor after the SCR. The computer compares it with the inlet sensor to see if the SCR is cleaning the exhaust.
Can I keep running with SPN 3226?
Fix it today. Finish what's safe to finish, then fix it this shift. Ignoring it usually turns into a derate or a bigger repair. If the machine derates or the stop lamp is on, stop.
What should I check first for SPN 3226?
Check DEF quality with a refractometer. Check the DEF doser for crystals. Check the sensor plug.
How do I clear SPN 3226?
Fix the cause first. Most codes go inactive by themselves once the condition is gone and the engine has run a key cycle or two. Clearing it with a service tool without a fix only hides it until it comes back.
Which machines show SPN 3226?
Any diesel that speaks SAE J1939: excavators, dozers, loaders, haul trucks, generators and on-road trucks with Cat, Cummins, Deere, Komatsu, Volvo, Kubota, Perkins and other engines. The SPN means the same thing on all of them; the fix steps can differ, so check the service manual.
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