What causes a SPN 433 code?

SPN 433 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 433 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 433 active.

How do I fix SPN 433?

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 433

J1939 SPN 433 — Fuel/Air parameter

What it means

FMI 18 indicates that the fuel rail pressure is lower than expected for the current engine operating conditions (Data Valid But Below Normal Operating Range).