What causes a SPN 40 code?

SPN 40 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 40 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 40 active.

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 40

J1939 SPN 40 — Engine parameter

What it means

Engine Parameter data is erratic, intermittent, or incorrect. This code is often a placeholder or 'root' code that accompanies more specific sensor codes.