What causes a SPN 305 code?

SPN 305 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 305 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 305 active.

How do I fix SPN 305?

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 305

J1939 SPN 305 — Fuel/Air parameter

What it means

Generic SAE J1939 identifier for Fuel/Air parameters, usually indicating a mismatch in intake air pressure or flow relative to fuel delivery.