P21FA: Fuel Control System B Too Lean at Idle (Bank 2)

What does P21FA mean?

P21FA is the bank 2 version of the idle lean check for the second fuel path. It applies to engines with two cylinder banks, a front oxygen sensor per bank and dual injection, such as Ford's 5.0 V8, which has combined port and direct injection since 2018. No manufacturer publishes this code; Ford monitors its port system per bank without separate idle cells and would store the fault as P2BF2. At idle the per-bank correction reacts strongly to small absolute errors, so a leak at bank 2's intake runners or gasket, or a partly blocked port injector on that side, are the first suspects while bank 1 stays clean. Drivers may notice an uneven idle or nothing beyond the warning lamp. The system A equivalent is P2189.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine lamp on
• Uneven idle

Common causes

• Medium Intake leak at bank 2 runners or gasket
• Medium Partly blocked port injector on bank 2
• Low Bank 2 front oxygen sensor reading lean

Likelihood is a general estimate across vehicles; your make and model may differ.