What causes a SPN 398 code?

SPN 398 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 398 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 398 active.

How do I fix SPN 398?

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 398

J1939 SPN 398 — Fuel/Air parameter

What it means

SPN 398 indicates a Fuel/Air Ratio mismatch, meaning the engine is not seeing the expected air volume for the amount of fuel being injected.