What causes a SPN 4005 code?

SPN 4005 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 4005 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4005 active.

How do I fix SPN 4005?

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 4005

Allison transmission code P4005

What it means

Transmission internal mechanical failure or slippage detected. This code is triggered when the TCM detects an incorrect gear ratio compared to input/output speeds.