What causes a SPN 994 code?

SPN 994 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 994 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 994 active.

How do I fix SPN 994?

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 994

J1939 SPN 994 — Engine Management parameter

What it means

SPN 994 refers to the Engine Cooling Fan Clutch Circuit. It indicates an electrical fault (open or short) in the command circuit for the fan drive.