What causes a SPN 4256 code?

SPN 4256 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 4256 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4256 active.

How do I fix SPN 4256?

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 4256

Cummins fault code 4256

What it means

Aftertreatment 1 SCR Intake Temperature - Data Erratic, Intermittent or Incorrect. This indicates the ECM is receiving an implausible signal from the SCR inlet temperature sensor.