P0299 on Ford Fiesta ST (2013–2017)

Platform-specific notes for diagnosing turbo underboost on the 1.6L EcoBoost Fiesta ST.

How P0299 Usually Shows Up on This Car

  • Noticeable drop in power, especially in the mid–high RPM range.
  • Boost gauge (if fitted) not reaching usual levels.
  • Often appears after fitting an intercooler, intake or remap if clamps aren’t fully sealed.
  • Sometimes accompanies lean codes (P0171) or misfire codes (P0300/P0301–P0304).

Common Fiesta ST–Specific Causes

  • Loose or poorly seated intercooler pipes after aftermarket upgrades.
  • Cracked plastic boost pipes or worn O-ring seals at quick-connect joints.
  • Wastegate actuator arm or pivot starting to stick, especially on higher mileage or tuned cars.
  • Weak or split vacuum hoses controlling the boost solenoid.

Suggested Test Plan

  1. Perform a careful visual inspection of all intercooler and boost pipes, looking for oil misting at joints.
  2. Carry out a smoke or low-pressure boost leak test to reveal small leaks you can’t see.
  3. Check wastegate actuator movement with a hand vacuum/pressure tool where possible.
  4. Log commanded vs actual boost on a safe test drive using a suitable scan tool.
  5. If all pipework and control systems test OK but underboost persists, inspect turbo condition for play or damage.

Where to Go Next

Use this page together with the generic P0299 explanation and the Fiesta ST car profile. For a tailored plan, feed all of your codes and symptoms into the AI OBD2 Code Explainer and specify the car as Ford Fiesta ST, 2013–2017, 1.6 EcoBoost.