What causes a SPN 3321 code?

SPN 3321 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 3321 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 3321 active.

How do I fix SPN 3321?

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 3321

J1939 SPN 3321 — Body/Chassis parameter

What it means

Aftertreatment 1 SCR Inlet Temperature Sensor - Voltage Above Normal, or Shorted to High Source. This indicates the ECM is detecting a signal voltage higher than the calibrated range, typical of an open circuit.