What causes a SPN 691 code?

SPN 691 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 691 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 691 active.

How do I fix SPN 691?

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 691

J1939 SPN 691 — Engine Management parameter

What it means

Engine Management Parameter Data Error. This code indicates that one or more internal configuration parameters in the ECM are incorrect, missing, or incompatible with the current engine hardware configuration.