What causes a SPN 6678 code?

SPN 6678 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 6678 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 6678 active.

How do I fix SPN 6678?

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 6678

Cummins fault code 6678

What it means

SCR Intake Temperature - Data Erratic, Intermittent, or Incorrect. This indicates the Aftertreatment Control Module detects that the SCR intake temperature sensor signal is not plausible compared to other engine temperature sensors.