What causes a P279A code?

P279A 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 P279A code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P279A active.

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

OBD-II

P279A

Shift Actuator 'A' Control Circuit/Open

What it means

This generic OBD-II Power train (P) code on Eaton systems indicates an open circuit issue with the 'A' shift actuator. This means the TCM is unable to control or detect feedback from this specific actuator.