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.
Medium severity. Can I keep driving?You can drive in moderation for a short time. A very lean or very rich mixture can damage the engine or the catalytic converter.
Bank 2 is the side without cylinder 1, so it only exists on V or boxer engines.
Symptoms
- Check engine lamp on
- Slight hesitation at part load
Most likely causes
- Restricted port injector on bank 2
- Wiring or connector fault on the bank 2 injector harness
- Low pressure in the shared port fuel rail (if bank 1 also lean)
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P21F6 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 1: Air and fuel
- F6: Specific fault in that system
Frequently asked questions
Can I keep driving with code P21F6?
You can drive in moderation for a short time. A very lean or very rich mixture can damage the engine or the catalytic converter.
What causes code P21F6?
The most common causes are: restricted port injector on bank 2; wiring or connector fault on the bank 2 injector harness; low pressure in the shared port fuel rail (if bank 1 also lean).
Related codes
- P21F4Fuel Control System B Too Lean Off Idle (Bank 1)
- P21F7Fuel Control System B Too Rich Off Idle (Bank 2)
- P21FAFuel Control System B Too Lean at Idle (Bank 2)
- P21FEFuel Control System B Too Lean at Higher Load (Bank 2)
- P2179System Too Lean Off Idle (Bank 2)
- P2BF2Fuel Control System B Too Lean Bank 2
Sources
- fordservicecontent.com: OBD Operations Summary Gasoline 2020 2023
- law.cornell.edu: 13 CCR 1968.2
- en.wikipedia.org: Ford Modular engine
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.