SPN 4334 FMI 18 — DEF pump pressure below target
What it means: DEF pump pressure below target.
How serious / can you keep driving: Caution. Limp to the next safe stop.
Check first: Check DEF filter condition
Don't risk it — look up listed providers near you and give them this SPN/FMI when you call.
Listed providers nearest Louisville, KY
Closest first. Tell them SPN 4334 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 Louisville, KY · (502) 773-1159
- 0.0 mi away — based in Louisville, KY · (502) 447-1234
- 0.0 mi away — based in Louisville, KY · (502) 648-6725
Applies to: Detroit · Navistar · Paccar · Sae · Volvo
What SPN 4334 FMI 18 means
DEF pump pressure below target.
How serious is it?
Caution. Limp to the next safe stop.
Most likely causes
- Failed DEF pump
- Clogged DEF filter
- Air leak in DEF supply
- Frozen DEF lines (winter)
- Low DEF level uncovering pickup
- Pump failed
- DEF filter clogged
First moves (roadside)
- Check DEF filter condition
- Verify pump runs at key-on
- Inspect lines for kinks/leaks/frost
- Check DEF level
- Check DEF filter
- Verify pump runs on key-on
- Inspect lines for kinks/leaks
Common misdiagnoses
- Replacing pump without checking filter first
FAQ
DEF pump pressure below target.
Caution — Limp to the next safe stop.
The most common cause is: Failed DEF pump. Other possibilities include Clogged DEF filter; Air leak in DEF supply; Frozen DEF lines (winter); Low DEF level uncovering pickup; Pump failed; DEF filter clogged.
Limp to the next safe stop. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Related codes
Codes that commonly appear alongside SPN 4334 FMI 18, or share the same subsystem.
- DEF pump pressure sensor — voltage high (SPN 4334 FMI 3)
- DEF pump pressure sensor — voltage low (SPN 4334 FMI 4)
- 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)
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 level low (SPN 1761 FMI 18) · 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
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.