What causes a SPN 343 code?

SPN 343 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 343 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 343 active.

How do I fix SPN 343?

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 343

J1939 SPN 343 — Fuel/Air parameter

What it means

SPN 343 indicates a 'Fuel/Air Control Parameter' error, typically signifying that the ECM has detected an internal mathematical error or a checksum failure regarding its fuel-to-air ratio calculation logic.