What causes a SPN 4374 code?

SPN 4374 can be triggered by several issues — see the verified probable causes and step-by-step diagnostics shared by mechanics and owners on OBDIY.

Can I drive with a SPN 4374 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4374 active.

How do I fix SPN 4374?

Follow the step-by-step diagnostic on this page, then read the verified fixes contributed by other Heavy Truck owners — the answer marked "Verified Cause" worked for the original poster.

OBDIY

J1939 SPN

SPN 4374

SPN 4374 — Aftertreatment 1 DEF Pump Motor Speed

What it means

Aftertreatment 1 Diesel Exhaust Fluid (DEF) Pump Motor Speed. This indicates the ECM/ACM detects that the DEF pump motor speed is not within the commanded range (often zero RPM or erratic).