What causes a SPN 389 code?

SPN 389 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 389 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 389 active.

How do I fix SPN 389?

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 389

J1939 SPN 389 — Fuel/Air parameter

What it means

Fuel/Air Ratio Parameter out of range or rational limit. The ECM has detected that the calculated fuel quantity does not correspond correctly with the measured air intake volume.