What causes a SPN 300 code?

SPN 300 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 300 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 300 active.

How do I fix SPN 300?

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 300

J1939 SPN 300 — Fuel/Air parameter

What it means

SPN 300 typically indicates a 'Fuel/Air Ratio' or 'Air Intake' system performance issue where the engine ECM detects that the measured air intake does not match the expected fueling rate.