Cummins Fault Code
Free · no signupSPN 4334 FMI 16
DEF Pressure High / Derate.
System
Aftertreatment
Symptom
DEF Pressure High / Derate.
Diagnosis & fix steps
LOGIC: DEF Dosing pressure is above the threshold.
ACTION: Check for a kinked or frozen DEF return line. If lines are clear, inspect the DEF injector for a nozzle blockage.
Red Seal field insights
Specs: Normal operating pressure is 500 kPa (72.5 psi).
PRO-TIP: In winter, DEF can crystalize in the "back-flow" line, causing a pressure spike.
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