SPN 4334 — Aftertreatment 1 DEF Doser Absolute Pressure
System: Aftertreatment / DEF
DEF pressure in the line between the DEF pump and the doser, used to confirm the pump is priming and holding pressure.
Can I keep running it?
HIGH — limit use, diagnose now
If the pump cannot build pressure, DEF is not dosing and inducement derates will follow.
Likely causes
- Air leak or worn O-rings on the suction line or tank header
- Clogged DEF pump filter or tank strainer
- Frozen or crystallized line
- Failed DEF pump
- Restricted or kinked return line
Checks & fixes (easiest first)
- Replace the DEF pump filter
- Run the pump prime test and watch whether pressure builds and holds
- Temporarily run a clear suction line to look for air bubbles
- Inspect lines for kinks, crystals or freezing
- Check pressure sensor reading key-on, engine-off
Common FMIs with SPN 4334
- SPN 4334 FMI 0Value too high (most severe)
- SPN 4334 FMI 1Value too low (most severe)
- SPN 4334 FMI 3Voltage above normal or shorted high
- SPN 4334 FMI 4Voltage below normal or shorted low
- SPN 4334 FMI 16Value too high (moderately severe)
- SPN 4334 FMI 18Value too low (moderately severe)
Related codes
- SPN 3361Aftertreatment 1 DEF Dosing Unit
- SPN 3363Aftertreatment 1 DEF Tank Heater
- SPN 4364Aftertreatment 1 SCR Conversion Efficiency
Troubleshooting guides
FAQ
What does SPN 4334 mean?
SPN 4334 is Aftertreatment 1 DEF Doser Absolute Pressure. DEF pressure in the line between the DEF pump and the doser, used to confirm the pump is priming and holding pressure.
Can I keep running with SPN 4334?
If the pump cannot build pressure, DEF is not dosing and inducement derates will follow.
What causes SPN 4334?
Air leak or worn O-rings on the suction line or tank header; Clogged DEF pump filter or tank strainer; Frozen or crystallized line; Failed DEF pump; Restricted or kinked return line.