P28F9Exhaust Pressure Too Low Bank 1
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P28F9 flags exhaust pressure on bank 1 that stays below what the engine should produce at the current load. Too little pressure ahead of the turbine means the gas is escaping or not being held back: a leak at the manifold, gasket or turbine inlet, an exhaust flap jammed open, or a variable turbine stuck wide open. No manufacturer documents P28F9 publicly. Ford's 2023 diesel summary shows how such a deviation can be caught: it compares the measured turbine upstream pressure with a modelled value and flags differences beyond -100 or +500 kPa, but files them under P0474 as a sensor fault. A system-level code like P28F9 instead assumes the sensor is right. CARB requires underboost monitoring on boosted engines. Expect weak boost, sluggish response and possibly louder exhaust noise.
- What you may notice
- Check engine light on
- Weak boost and sluggish acceleration
- Ticking or hissing exhaust noise near the manifold
- Likely causes
- LikelyExhaust leak at manifold, gasket or turbine inlet on bank 1
- PossibleVariable turbine geometry stuck in the open position
- PossibleExhaust throttle or pressure flap jammed open
- RareLeaking or cracked sensing tube to the exhaust pressure sensor
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €100 – €2,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.