P21F6 Fuel Control System B Too Lean Off Idle (Bank 2)

P21F6 is the bank 2 form of P21F4 and only exists on V or flat engines whose cylinder banks each have their own front oxygen sensor and two injection paths. Here the part-load correction of the second path on bank 2 has reached its lean limit. No manufacturer documents this code publicly. Ford, whose 5.0 Coyote V8 gained direct injection on top of port injection for 2018, reports a lean port-injection fault on bank 2 as P2BF2 instead, without load zones, once long-term trim exceeds 25 % together with short-term trim above 1 % for 2 s. CARB demands a fault once adaptive control has used up its permitted range. If bank 1 stays clean, look at bank 2 alone: a clogged port injector or a wiring fault on that bank's injector harness.

Likely causes

Symptoms

• Check engine lamp on
• Slight hesitation at part load

Repair estimate

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

Parts involved

Related codes

References: fordservicecontent.com, law.cornell.edu, en.wikipedia.org.