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SPN 1761 FMI 18 — DEF tank level low
SeriousAftertreatmentPower derate likely — plan to stop soon
Applies to: Detroit · Navistar · Paccar · Volvo
DEF tank level low.
Don't risk it — get a diesel tech on the truck.
Your SPN/FMI rides along, so nearby mechanics see the fault before they quote you.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Actual low DEF
- Failed level sender
- Actual low
- Failed sensor
- Failed sender
First moves (roadside)
- Refill DEF
- Check sensor if full
- Refill
- Check sensor
FAQ
What does SPN 1761 FMI 18 mean?
DEF tank level low.
How serious is SPN 1761 FMI 18?
Serious — Power derate likely — plan to stop soon.
What's the most likely cause of SPN 1761 FMI 18?
The most common cause is: Actual low DEF. Other possibilities include Failed level sender; Actual low; Failed sensor; Failed sender.
Can I keep driving with SPN 1761 FMI 18?
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Throwing this code right now?
Find a mechanic or related guides
General diagnostic guidance for heavy-duty diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack). Not a substitute for a scan-tool diagnosis on your specific truck.