What causes a SPN 4409 code?

SPN 4409 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 4409 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4409 active.

How do I fix SPN 4409?

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 4409

Allison transmission code P4409

What it means

Reverse Pressure Switch Malfunction. This code indicates that the TCM has detected an illogical state for the reverse pressure switch (e.g., the switch indicates pressure when reverse is not commanded, or no pressure when reverse is commanded).