What causes a SPN 402 code?

SPN 402 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 402 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 402 active.

How do I fix SPN 402?

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 402

J1939 SPN 402 — Fuel/Air parameter

What it means

SPN 402 is a generic J1939 fault indicating a data integrity issue within the Fuel/Air calculation system, most frequently tied to EGR temperature or internal ECM monitoring of intake airflow parameters.