What causes a SPN 4402 code?

SPN 4402 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 4402 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4402 active.

How do I fix SPN 4402?

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 4402

Allison transmission code P4402

What it means

SPN 4402 (Standard Allison P-code P4402) indicates a 'Transmission Control System Performance' issue, specifically related to unexpected mechanical ratio data or a stuck clutch component.