What causes a P0509 code?

P0509 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 P0509 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P0509 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

P0509

Idle Air Control System Circuit High

What it means

The Engine Control Module (ECM) has detected a higher than normal voltage signal in the Idle Air Control (IAC) circuit, indicating an electrical fault or blocked passage.