What causes a SPN 6349 code?

SPN 6349 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 6349 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 6349 active.

How do I fix SPN 6349?

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 6349

Cummins fault code 6349

What it means

P0422 Equivalent / SCR Nitrogen Oxides (NOx) Conversion Efficiency - Low. The aftertreatment system is not reducing NOx emissions effectively enough to meet the threshold required by the ECM.