What causes a SPN 306 code?

SPN 306 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 306 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 306 active.

How do I fix SPN 306?

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 306

J1939 SPN 306 — Fuel/Air parameter

What it means

SPN 306 is a generic FMI-dependent code indicating a 'Fuel/Air' rationality fault. This means the ECM detects an imbalance between the amount of air entering the engine and the amount of fuel being injected, or a sensor associated with this ratio is reporting invalid data.