What causes a SPN 4009 code?

SPN 4009 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 4009 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4009 active.

How do I fix SPN 4009?

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 4009

Allison transmission code P4009

What it means

The TCM has detected a low current or open circuit condition on the solenoid internal power supply circuit or a specific clutch solenoid control circuit.