What causes a SPN 238 code?

SPN 238 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 238 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 238 active.

How do I fix SPN 238?

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 238

J1939 SPN 238 — Fuel/Air parameter

What it means

Accessory Cost Mean Speed. This is typically a parameter used for calculating auxiliary fuel or air usage but can indicate a signal error in J1939 data.