What causes a SPN 3239 code?

SPN 3239 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 3239 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 3239 active.

How do I fix SPN 3239?

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 3239

SPN 3239 FMI 13 - Aftertreatment 1 SCR Intermediate Gas Sensor Calibration Out of Range

What it means

This fault indicates that the SCR intermediate NOx sensor (located between the SCR catalyst stages) has failed its internal calibration check during a zero-calibration event.