What causes a SPN 3256 code?

SPN 3256 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 3256 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 3256 active.

How do I fix SPN 3256?

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 3256

Aftertreatment 1 Intake Temperature Sensor High Voltage

What it means

The Engine Control Module (ECM) detects that the sensor signal voltage for the Aftertreatment Intake Temperature is above the normal operating range, typically indicating an open circuit or short to power.