What causes a SPN 4606 code?

SPN 4606 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 4606 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4606 active.

How do I fix SPN 4606?

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 4606

Allison transmission code P4606

What it means

Transmission Range Logic Fault - This code indicates that the Transmission Control Module (TCM) has detected an invalid combination of pressure switch inputs, suggesting the transmission is in multiple ranges simultaneously or an impossible gear state.