What causes a SPN 4004 code?

SPN 4004 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 4004 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4004 active.

How do I fix SPN 4004?

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 4004

Allison transmission code P4004

What it means

Allison internal code often associated with a 'Range Monitor' or 'Stuck in Neutral' issue where the requested gear does not match the actual gear ratio detected by the speed sensors.