What causes a SPN 4305 code?

SPN 4305 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 4305 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4305 active.

How do I fix SPN 4305?

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 4305

Allison transmission code P4305

What it means

P4305: Transmission Input Shaft Speed Sensor Circuit - No Signal While In Gear. Often indicates a mechanical failure where the input shaft is not rotating despite engine speed or a total sensor signal loss.