What causes a SPN 939 code?

SPN 939 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 939 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 939 active.

How do I fix SPN 939?

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 939

J1939 SPN 939 — Engine Management parameter

What it means

Engine Management Parameter mismatch or communication error. This code indicates the ECM is receiving data that is out of range, missing, or corrupted regarding its internal management strategy or specific configuration parameters.