What causes a SPN 318 code?

SPN 318 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 318 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 318 active.

How do I fix SPN 318?

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 318

J1939 SPN 318 — Fuel/Air parameter

What it means

SPN 318 indicates an 'Air/Fuel Ratio' or 'Fuel/Air' parameter error, signaling that the engine ECM has detected that the ratio of air to fuel is outside of the calibrated limits for efficient combustion and emissions control.