P21FCFuel Control System B Too Lean at Higher Load (Bank 1)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P21FC is the lean check of bank 1's second fuel path in the upper load zone, the third cell next to idle (P21F8) and part load (P21F4). Under high load, delivery capacity matters most: a weak lift pump, a clogged filter or a low-pressure rail that sags at high flow show up here first. On engines combining both paths, the share of each depends on the operating point; Audi's 2.5 TFSI, for example, uses 95 % direct and only 5 % manifold injection at heavy load during warm-up, so the second path's share and its trim learning vary strongly. No manufacturer documents P21FC publicly; Audi's bulletin for that engine covers only the idle and off-idle codes. Hesitation under full load is possible. P2191 is the system A counterpart.
- What you may notice
- Check engine lamp on
- Hesitation or power loss at full load
- Likely causes
- LikelyWeak in-tank lift pump or clogged fuel filter
- PossiblePort rail pressure dropping at high flow
- PossiblePort injectors on bank 1 flowing too little
- RareCharge air leak behind the air mass 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: €50 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.