What causes a SPN 4578 code?

SPN 4578 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 4578 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4578 active.

How do I fix SPN 4578?

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 4578

Cummins fault code 4578

What it means

Aftertreatment 1 Diesel Exhaust Fluid Dosing Unit - Loss of Prime / Under-Efficiency. This code indicates the SCR system is not effectively reducing NOx because the DEF is not being sprayed or atomized correctly.