What causes a SPN 4400 code?

SPN 4400 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 4400 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4400 active.

How do I fix SPN 4400?

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 4400

Allison transmission code P4400

What it means

P4400 refers specifically to a 'C6 Clutch Stuck On' condition. This indicates that the 6th gear clutch is engaged when the Transmission Control Module (TCM) expects it to be disengaged.