SPN 1761 FMI 18 — DEF tank level low
What it means: DEF tank level low.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Refill DEF
Don't risk it — look up listed providers near you and give them this SPN/FMI when you call.
Listed providers nearest Salt Lake City, UT
Closest first. Tell them SPN 1761 FMI 18 and what the truck is doing. RoadService.app lists these providers and does not employ them or carry out the repair.
- 0.0 mi away — based in Salt Lake City, UT · (801) 531-9256
- 0.0 mi away — based in Salt Lake City, UT · (385) 503-8084
- 0.0 mi away — based in Salt Lake City, UT · (385) 386-4700
Applies to: Detroit · Navistar · Paccar · Volvo
What SPN 1761 FMI 18 means
DEF tank level low.
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
DEF tank level low.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Actual low DEF. Other possibilities include Failed level sender; Actual low; Failed sensor; Failed sender.
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Related codes
Codes that commonly appear alongside SPN 1761 FMI 18, or share the same subsystem.
- DEF Tank Level — Low (SPN 1761 FMI 1)
- SCR Operator Inducement — Severe Derate Active (SPN 5246 FMI 0)
- Aftertreatment 1 Diesel Particulate Filter Differential Pressure - Data Valid But Above Normal Operating Range, Most Severe Level (DPF severely restricted / plugged) (SPN 3251 FMI 0)
- Aftertreatment 1 Diesel Exhaust Fluid Quality - Data Valid But Below Normal Operating Range, Most Severe Level (DEF quality/concentration incorrect) (SPN 4364 FMI 1)
- DPF Differential Pressure — Data Erratic (SPN 3251 FMI 2)
- DEF Dosing Unit — Not Responding Properly (SPN 3361 FMI 7)
- SCR Conversion Efficiency — Below Threshold (SPN 4364 FMI 18)
- DEF Quality — Out of Spec (SPN 4094 FMI 31)
Same symptom: DEF / SCR fault
Other codes in the DEF and SCR chain — the ones that end in an inducement countdown.
- Reductant System Performance Bank 1 (P204F) · Aftertreatment & Emissions
- Reductant Quality Deviation (P20EA) · Aftertreatment & Emissions
- DEF tank temp sensor — voltage high (SPN 3031 FMI 3) · Aftertreatment & Emissions
- Upstream NOx sensor — internal failure reported (SPN 3216 FMI 12) · Aftertreatment & Emissions
- SCR inlet NOx sensor — erratic (SPN 3216 FMI 2) · Aftertreatment & Emissions
- Upstream NOx sensor — abnormal update rate (SPN 3216 FMI 9) · Aftertreatment & Emissions
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.