Detroit Diesel SPN 4374 FMI 18 – DEF Doser Valve Current Low (Meaning, Causes & Fix)

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Detroit Diesel SPN 4374 FMI 18 indicates that the electrical current to the DEF doser valve is below the expected threshold. This code appears on DD13, DD15, and DD16 engines and points to an electrical fault in the DEF dosing circuit that is preventing the doser valve from operating correctly, which will affect SCR system performance and can lead to a derate condition.

Symptoms

  • Check engine light on
  • DEF or SCR warning light illuminated
  • Engine derate condition possible
  • DEF dosing system not functioning correctly
  • May appear alongside other doser valve or DEF system codes

Cause

This code triggers when the ECM detects lower than expected current draw from the DEF doser valve circuit. Common causes include:

  • Open circuit in the doser valve wiring harness
  • Damaged or corroded doser valve connector
  • Failed doser valve solenoid with low resistance
  • Broken wire between ECM and doser valve
  • Water intrusion in the doser valve connector
  • Faulty ECM output driver for the doser valve circuit

Can You Keep Driving?

Limited driving may be possible but without proper electrical function the DEF doser valve cannot operate correctly and the SCR system will be unable to control DEF delivery. A derate condition is likely if the fault is not resolved promptly.

Recommended Action

Inspect the DEF doser valve wiring harness and connector for damage, corrosion, or broken wires. Check for water intrusion at the connector. Test the doser valve solenoid resistance against specification. If wiring and connector are intact and the solenoid tests good have the ECM output circuit evaluated by a qualified technician.

What does Detroit Diesel SPN 4374 FMI 18 mean?

It means the electrical current to the DEF doser valve is below the expected level, indicating an electrical fault in the dosing circuit that prevents proper valve operation.

What causes SPN 4374 FMI 18?

The most common causes are an open circuit or broken wire in the doser valve harness, a corroded connector, water intrusion at the connector, or a failed doser valve solenoid.

Can I keep driving with SPN 4374 FMI 18?

Short distances may be possible but without correct electrical supply the doser valve cannot function and the SCR system will be compromised, leading to a likely derate condition.

Will SPN 4374 FMI 18 cause a derate?

Yes. If the doser valve cannot operate due to low current the SCR system will be unable to deliver DEF correctly and the ECM will trigger a derate condition.

How do I clear SPN 4374 FMI 18?

Inspect and repair the doser valve wiring and connector. Test the solenoid and replace the valve if faulty. Once the ECM confirms correct current draw to the doser valve the code should clear.

Related codes

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Important Notice

The information provided above is for general informational purposes only and should not replace official OEM service procedures. Always consult the manufacturer’s service manual or a qualified diesel technician before performing repairs. Operating a vehicle with active fault codes may result in further damage.