What causes a SPN 5278 code?

SPN 5278 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 5278 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 5278 active.

How do I fix SPN 5278?

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 5278

Cummins fault code 5278

What it means

Aftertreatment 1 SCR Catalyst Efficiency - Data Valid But Below Normal Operating Range - Least Severe Level. The ECM has detected that the NOx reduction efficiency of the SCR system is lower than the required threshold.