Powertrain, generic (extended)

P21FC Fuel Control System B Too Lean at Higher Load (Bank 1)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Weak in-tank lift pump or clogged fuel filter
Port rail pressure dropping at high flow
Port injectors on bank 1 flowing too little
Charge air leak behind the air mass sensor

Symptoms

  • Check engine lamp on
  • Hesitation or power loss at full load

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–900
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel pressure regulatorfuel injectorcharge air pipe

Related codes

P21FDP21FEP21F4P21F8P2191P2BF0

References: static.nhtsa.gov, law.cornell.edu, fordservicecontent.com.