What causes a SPN 7861 code?

SPN 7861 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 7861 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 7861 active.

How do I fix SPN 7861?

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 7861

Cummins fault code 7861

What it means

Aftertreatment 1 Outlet NOx 2 - Abnormal Update Rate. This code indicates the Engine Control Module (ECM) has lost communication with the secondary downstream NOx sensor or is receiving invalid data packets over the J1939 data link.