What causes a SPN 6391 code?

SPN 6391 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 6391 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 6391 active.

How do I fix SPN 6391?

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 6391

Cummins fault code 6391

What it means

Aftertreatment 1 SCR Inlet Temperature - Data Erratic, Intermittent, or Incorrect. This specifically points to an issue where the ECM detects the SCR inlet temperature sensor signal is out of range or inconsistent with other sensor readings.