P259E: A low boost-control limit uses a large sustained pressure error

P259E names turbocharger A boost control position at low limit. Ford’s diesel monitor defines the listed failure through desired boost pressure minus actual boost pressure, not a universal actuator-position percentage.

Engine-specific pressure and time limits

For the documented 6.7L strategy, the deviation exceeds 120 kPa; the 3.0L example uses 80 kPa. Typical durations are ten and eleven seconds respectively. Closed-loop boost control must be enabled, with valid coolant-temperature, manifold-pressure, air-mass, and turbo-position inputs.

The entry conditions also distinguish engine torque and speed between variants. That matters when interpreting a fault log: the same pressure shortfall at an ineligible operating point is not automatically the same completed control-limit check.

Do not infer a mechanical stop from the title alone

The phrase “position at low limit” may invite an immediate actuator diagnosis, but the published threshold here is a pressure-control error. A useful investigation preserves target and actual boost together and identifies the applicable engine calibration.

P2263 is a separate, smaller-deviation accumulated underboost monitor on the same page. Its duration and counter logic should not be applied to P259E. The source does not determine whether the pressure error comes from an air-path condition, actuator behavior, measurement error, or another cause. The correct vehicle service tests are needed before selecting a component for repair.

Source and applicability

This explanation follows Ford’s 2023–2024 diesel OBD summary. Match the vehicle’s engine and calibration before applying these monitor values; a generic code alone does not establish fitment. Ford PDF, page 46.