What causes a SPN 401 code?

SPN 401 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 401 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 401 active.

How do I fix SPN 401?

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 401

J1939 SPN 401 — Fuel/Air parameter

What it means

SPN 401 specifically refers to 'Engine Fan Speed.' It monitors the rotational speed of the engine fan relative to the commanded signal. Failure indicates the ECM detects the fan is spinning at an incorrect speed.