What causes a SPN 4901 code?

SPN 4901 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 4901 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4901 active.

How do I fix SPN 4901?

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 4901

Allison transmission code P4901

What it means

Primary Software Incompatible with Hardware. This occurs when the TCM detects that the flashed operating system or calibration software pack is not compatible with the physical TCM hardware generation (e.g., trying to load Gen 5 software onto a Gen 4 TCM).