SPN 4334 FMI 18: DEF doser pressure, below normal, moderately severe
DEF pressure at the doser is too low. Type another SPN and FMI to check it.
DEF pressure at the doser is too low.
- Check the DEF level and filter.
- Look for leaks or a kinked suction line.
- Check the pump.
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 4334 FMI 18 means
DEF pressure at the doser is too low.
FMI 18: below normal, moderately severe
Low enough to matter. Fix it before it gets worse. (SAE J1939-73: Data valid but below normal operating range, moderately severe level.)
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 the DEF level and filter.
- Look for leaks or a kinked suction line.
- Check the pump.
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 4334
| Code | What failed | Urgency |
|---|---|---|
| SPN 4334 FMI 3 | voltage high or shorted high | Fix it today |
| SPN 4334 FMI 4 | voltage low or shorted low | Fix it today |
| SPN 4334 FMI 16 | above normal, moderately severe | 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.
Email me the PDF
We'll send this to you as a PDF, plus a reminder if there's a date in it. One email, no list.
We use it to send this and nothing else. See privacy.
Questions crews ask
What does SPN 4334 FMI 18 mean?
DEF pressure at the doser is too low. FMI 18 means: Low enough to matter. Fix it before it gets worse.
Can I keep running with SPN 4334 FMI 18?
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 4334 FMI 18?
Check the DEF level and filter. Look for leaks or a kinked suction line. Check the pump.
How do I clear SPN 4334 FMI 18?
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 4334 FMI 18?
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.
Related free tools
Your site at 6 a.m., before you're there.
Free for one site and one camera. $99 a site after. Crew is always free. 7 days of everything free, no card.