What causes a SPN 408 code?

SPN 408 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 408 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 408 active.

How do I fix SPN 408?

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 408

J1939 SPN 408 — Fuel/Air parameter

What it means

SPN 408 is a general parameter code indicating an imbalance or incorrect reading in the Fuel/Air ratio mixing logic, often related to air flow or intake pressure sensors.