What causes a P1566 code?

P1566 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 P1566 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P1566 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

P1566

Idle diagnostic fuel error fault

What it means

The Engine Control Module (ECM) has detected that the amount of fuel required to maintain the desired idle speed is outside of the calibrated parameters, typically indicating a leak or a mechanical efficiency issue.