What causes a SPN 971 code?

SPN 971 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 971 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 971 active.

How do I fix SPN 971?

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 971

SPN 971 Engine Derate Switch Input Fault

What it means

Indicates a communication or signal issue with the engine derate switch, which allows the operator to manually initiate a performance reduction or acknowledge specific fault conditions.