Powertrain, generic (extended)

P21FB Fuel Control System B Too Rich at Idle (Bank 2)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P21FB means bank 2's second fuel path is rich at idle while its correction already sits at the rich limit. The code requires an engine with a separate front sensor per bank and two injection paths; no maker documents it publicly. CARB section (e)(6.2.2) is the legal basis: once adaptive fuel control has used up the adjustment the manufacturer allows, a fault must be stored. Rich idle on one bank only typically comes from a port injector on that bank that leaks or sticks open, or from a bank 2 front sensor that reports too rich. If both banks show rich idle codes, look at shared items such as low-pressure regulation or fuel entering through crankcase ventilation. Fuel smell and a rough idle are possible; P2190 is the system A sibling.

Likely causes

Port injector on bank 2 leaking or sticking open
Bank 2 front oxygen sensor reading rich
Low-pressure regulation too high or fuel from crankcase ventilation (if both banks rich)

Symptoms

  • Check engine lamp on
  • Rough idle and fuel smell

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–800
Time0.5–3.5 h

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

Parts involved

fuel injector

Related codes

P21FAP21F9P21F7P21FFP2190P2BF3

References: law.cornell.edu, fordservicecontent.com.