What causes a SPN 494 code?

SPN 494 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 494 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 494 active.

How do I fix SPN 494?

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 494

J1939 SPN 494 — Fuel/Air parameter

What it means

The Engine Control Module (ECM) has detected an abnormality in the calculated Fuel/Air ratio parameters, suggesting the mixture is outside of calibrated limits.