What causes a SPN 904 code?

SPN 904 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 904 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 904 active.

How do I fix SPN 904?

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 904

J1939 SPN 904 — Engine Management parameter

What it means

SPN 904 specifically refers to the Front Axle Speed. In the J1939 architecture, this indicates the engine controller is receiving invalid, intermittent, or missing data regarding the front axle speed, which is critical for cruise control and torque management.