SPN 4374: Aftertreatment DEF Pump
What SPN 4374 Is
SPN 4374 is the aftertreatment DEF pump. On Cummins lists it appears as Aftertreatment 1 DEF Pump 1 Motor Speed (FMI 2, 5, 20, 31). In the bay it shows up as no DEF pressure, failed quantity tests, and crystallization at the pump vents.
Reddit and shop tickets often log SPN 4374 FMI 0 with a 25% derate after a heavy pull. That is still a pump/supply problem until a flow test says otherwise — not an SCR brick.
Common FMI Combinations
| FMI | Meaning | Start here |
|---|---|---|
| 2 | Erratic motor speed | Filter, aeration, failing pump |
| 5 | Open circuit | Connector, pump motor |
| 0 / 20 / 31 | Speed/pressure out of range or condition exists | OEM DEF pump flow test |
Diagnostic Order
- Confirm DEF is present and not frozen. Empty or gelled fluid is not a pump.
- Service the pump filter / strainer. Crystals here are routine.
- Look at pump vents for wetness. A pump leaking from the vents is a pump, not a harness.
- Run the OEM volume/pressure test (Detroit 108–132 mL on many GHG procedures; Cummins INSITE DEF flow). Replace the pump only if the test fails with a known-good supply.
Companions: 3364 quality, dosing valve SPNs, then efficiency 4364. Hardware on our sessions: Nexiq USB-Link 3 and a rugged diagnostic laptop.
Frequently Asked Questions
Remote diagnostics · 24/7 · Hablamos Español
Start a remote diagnostic session
A Torque Edge technician can connect live with a Nexiq USB-Link 3 and a rugged diesel diagnostic laptop. If you already have an adapter, we use yours. If you don't, we have the kit on our side — you don't wait on a dealer.
or request a callback
Need the hardware in your shop? Nexiq USB-Link 3 · Diagnostic laptop