P21F7: Fuel Control System B Too Rich Off Idle (Bank 2)

What does P21F7 mean?

P21F7 sets when the second fuel path on bank 2 has to remove more fuel above idle than its rich limit permits. It needs an engine with two banks, separate front sensors and dual injection; inline engines such as Audi's 2.5 TFSI only have the bank 1 codes. No manufacturer publishes criteria for P21F7. An FCA patent for port plus direct injection engines explains the idea behind such split codes: a fault seen while only one path is fuelling is assigned to that path, whereas a fault during mixed operation goes to a general code such as P0175. When only this bank is affected, a leaking port injector on bank 2 or a bank 2 front sensor that reads rich is plausible; if both banks are rich, check what they share, such as pressure regulation. P2180 is the system A counterpart.

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

Symptoms

• Check engine lamp on
• Increased fuel consumption

Common causes

• Medium Leaking port injector on bank 2
• Medium Bank 2 front oxygen sensor reading rich
• Low Low-pressure regulation too high (if bank 1 also rich)

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