What causes a SPN 291 code?

SPN 291 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 291 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 291 active.

How do I fix SPN 291?

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 291

J1939 SPN 291 — Fuel/Air parameter

What it means

SPN 291 typically refers to Fan Drive Response State. It indicates that the ECM has detected a mismatch between the commanded fan speed/state and the actual feedback received, or an electrical fault in the fan control circuit.