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SPN 4374 FMI 5 — DEF pump relay — open
SeriousAftertreatmentPower derate likely — plan to stop soon
Applies to: Sae
DEF pump relay — open.
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
- Open relay coil
- Open wire
First moves (roadside)
- Swap relay
- Check coil drive
FAQ
What does SPN 4374 FMI 5 mean?
DEF pump relay — open.
How serious is SPN 4374 FMI 5?
Serious — Power derate likely — plan to stop soon.
What's the most likely cause of SPN 4374 FMI 5?
The most common cause is: Open relay coil. Other possibilities include Open wire.
Can I keep driving with SPN 4374 FMI 5?
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.