What causes a SPN 394 code?

SPN 394 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 394 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 394 active.

How do I fix SPN 394?

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 394

J1939 SPN 394 — Fuel/Air parameter

What it means

SPN 394 indicates a generic 'Fuel/Air' parameter error, typically signifying that the Engine Control Module (ECM) has detected a discrepancy in the calculated air-fuel ratio or an issue with the trim data required to maintain combustion efficiency.