What causes a SPN 308 code?

SPN 308 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 308 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 308 active.

How do I fix SPN 308?

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 308

J1939 SPN 308 — Fuel/Air parameter

What it means

SPN 308 indicates a generic fault in the Fuel/Air ratio parameters, suggesting the Engine Control Module (ECM) is detecting intake air flow or air density data that deviates from expected values for current fuel injection rates.